Re: [PATCH 00/14] Pramfs: Persistent and protected ram filesystem
On Sun 2009-06-28 19:33:02, Marco Stornelli wrote: Pavel Machek wrote: Ah now the write protection is a needed feature, in your previous comment you talked about why not use ext2/3... Marco Just for your information I tried the same test with pc in a virtual machine with 32MB of RAM: Version 1.03e --Sequential Output-- --Sequential Input- --Random- -Per Chr- --Block-- -Rewrite- -Per Chr- --Block-- --Seeks-- Machine Size:chnk K/sec %CP K/sec %CP K/sec %CP K/sec %CP K/sec %CP /sec %CP hostname 15M:1k 14156 99 128779 100 92240 100 11669 100 166242 99 80058 82 --Sequential Create-- Random Create -Create-- --Read--- -Delete-- -Create-- --Read--- -Delete-- files /sec %CP /sec %CP /sec %CP /sec %CP /sec %CP /sec %CP 4 2842 99 133506 104 45088 101 2787 99 79581 101 58212 102 These data are the proof of the importance of the environment, workload and so on when we talk about benchmark. Your consideration are really superficial. Unfortunately, your numbers are meaningless. I don't think so. (PCs should have cca 3GB/sec RAM transfer rates; and you demosstrated cca 166MB/sec read rate; disk is 80MB/sec, so that's too slow. If you want to prove your filesystem the filesystem is reasonably fast, compare it with ext2 on ramdisk.) This is the point. I don't want compare it with ext2 from performance point of view. This comparison makes no sense for me. I've done this test to prove that if you change environment you can change in a purposeful way the results. Yes, IOW you demonstrated that the numbers are machine-dependend and really meaningless. ext2 comparison would tell you how much pramfs sucks (or not). Here the test with ext2 (same environment): Version 1.03e --Sequential Output-- --Sequential Input- --Random- -Per Chr- --Block-- -Rewrite- -Per Chr- --Block-- --Seeks-- Machine Size:chnk K/sec %CP K/sec %CP K/sec %CP K/sec %CP K/sec %CP /sec %CP hostname 15M:1k 10262 83 40847 82 38574 82 9866 92 62252 98 25204 81 --Sequential Create-- Random Create -Create-- --Read--- -Delete-- -Create-- --Read--- -Delete-- files /sec %CP /sec %CP /sec %CP /sec %CP /sec %CP /sec %CP 1 19859 98 44804 61 68830 100 13566 99 157129 100 30431 98 Ok, so pramfs is significantly faster than ext2. Interesting, and good for pramfs. Pavel -- (english) http://www.livejournal.com/~pavelmachek (cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html -- To unsubscribe from this list: send the line unsubscribe linux-embedded in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: [PATCH 00/14] Pramfs: Persistent and protected ram filesystem
Ah now the write protection is a needed feature, in your previous comment you talked about why not use ext2/3... Marco Just for your information I tried the same test with pc in a virtual machine with 32MB of RAM: Version 1.03e --Sequential Output-- --Sequential Input- --Random- -Per Chr- --Block-- -Rewrite- -Per Chr- --Block-- --Seeks-- Machine Size:chnk K/sec %CP K/sec %CP K/sec %CP K/sec %CP K/sec %CP /sec %CP hostname 15M:1k 14156 99 128779 100 92240 100 11669 100 166242 99 80058 82 --Sequential Create-- Random Create -Create-- --Read--- -Delete-- -Create-- --Read--- -Delete-- files /sec %CP /sec %CP /sec %CP /sec %CP /sec %CP /sec %CP 4 2842 99 133506 104 45088 101 2787 99 79581 101 58212 102 These data are the proof of the importance of the environment, workload and so on when we talk about benchmark. Your consideration are really superficial. Unfortunately, your numbers are meaningless. I don't think so. (PCs should have cca 3GB/sec RAM transfer rates; and you demosstrated cca 166MB/sec read rate; disk is 80MB/sec, so that's too slow. If you want to prove your filesystem the filesystem is reasonably fast, compare it with ext2 on ramdisk.) This is the point. I don't want compare it with ext2 from performance point of view. This comparison makes no sense for me. I've done this test to prove that if you change environment you can change in a purposeful way the results. Yes, IOW you demonstrated that the numbers are machine-dependend and really meaningless. ext2 comparison would tell you how much pramfs sucks (or not). Pavel -- (english) http://www.livejournal.com/~pavelmachek (cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html -- To unsubscribe from this list: send the line unsubscribe linux-embedded in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: [PATCH 00/14] Pramfs: Persistent and protected ram filesystem
Pavel Machek wrote: Ah now the write protection is a needed feature, in your previous comment you talked about why not use ext2/3... Marco Just for your information I tried the same test with pc in a virtual machine with 32MB of RAM: Version 1.03e --Sequential Output-- --Sequential Input- --Random- -Per Chr- --Block-- -Rewrite- -Per Chr- --Block-- --Seeks-- Machine Size:chnk K/sec %CP K/sec %CP K/sec %CP K/sec %CP K/sec %CP /sec %CP hostname 15M:1k 14156 99 128779 100 92240 100 11669 100 166242 99 80058 82 --Sequential Create-- Random Create -Create-- --Read--- -Delete-- -Create-- --Read--- -Delete-- files /sec %CP /sec %CP /sec %CP /sec %CP /sec %CP /sec %CP 4 2842 99 133506 104 45088 101 2787 99 79581 101 58212 102 These data are the proof of the importance of the environment, workload and so on when we talk about benchmark. Your consideration are really superficial. Unfortunately, your numbers are meaningless. I don't think so. (PCs should have cca 3GB/sec RAM transfer rates; and you demosstrated cca 166MB/sec read rate; disk is 80MB/sec, so that's too slow. If you want to prove your filesystem the filesystem is reasonably fast, compare it with ext2 on ramdisk.) This is the point. I don't want compare it with ext2 from performance point of view. This comparison makes no sense for me. I've done this test to prove that if you change environment you can change in a purposeful way the results. Yes, IOW you demonstrated that the numbers are machine-dependend and really meaningless. ext2 comparison would tell you how much pramfs sucks (or not). Pavel If you knew that the results were machine-dependent I don't understand why you were so upset by my previous benchmark. Marco -- To unsubscribe from this list: send the line unsubscribe linux-embedded in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: [PATCH 00/14] Pramfs: Persistent and protected ram filesystem
Pavel Machek wrote: Ah now the write protection is a needed feature, in your previous comment you talked about why not use ext2/3... Marco Just for your information I tried the same test with pc in a virtual machine with 32MB of RAM: Version 1.03e --Sequential Output-- --Sequential Input- --Random- -Per Chr- --Block-- -Rewrite- -Per Chr- --Block-- --Seeks-- Machine Size:chnk K/sec %CP K/sec %CP K/sec %CP K/sec %CP K/sec %CP /sec %CP hostname 15M:1k 14156 99 128779 100 92240 100 11669 100 166242 99 80058 82 --Sequential Create-- Random Create -Create-- --Read--- -Delete-- -Create-- --Read--- -Delete-- files /sec %CP /sec %CP /sec %CP /sec %CP /sec %CP /sec %CP 4 2842 99 133506 104 45088 101 2787 99 79581 101 58212 102 These data are the proof of the importance of the environment, workload and so on when we talk about benchmark. Your consideration are really superficial. Unfortunately, your numbers are meaningless. I don't think so. (PCs should have cca 3GB/sec RAM transfer rates; and you demosstrated cca 166MB/sec read rate; disk is 80MB/sec, so that's too slow. If you want to prove your filesystem the filesystem is reasonably fast, compare it with ext2 on ramdisk.) This is the point. I don't want compare it with ext2 from performance point of view. This comparison makes no sense for me. I've done this test to prove that if you change environment you can change in a purposeful way the results. Yes, IOW you demonstrated that the numbers are machine-dependend and really meaningless. ext2 comparison would tell you how much pramfs sucks (or not). Pavel Here the test with ext2 (same environment): Version 1.03e --Sequential Output-- --Sequential Input- --Random- -Per Chr- --Block-- -Rewrite- -Per Chr- --Block-- --Seeks-- Machine Size:chnk K/sec %CP K/sec %CP K/sec %CP K/sec %CP K/sec %CP /sec %CP hostname 15M:1k 10262 83 40847 82 38574 82 9866 92 62252 98 25204 81 --Sequential Create-- Random Create -Create-- --Read--- -Delete-- -Create-- --Read--- -Delete-- files /sec %CP /sec %CP /sec %CP /sec %CP /sec %CP /sec %CP 1 19859 98 44804 61 68830 100 13566 99 157129 100 30431 98 Marco -- To unsubscribe from this list: send the line unsubscribe linux-embedded in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: [PATCH 00/14] Pramfs: Persistent and protected ram filesystem
If it loses power when doing atomic rename (to replace config files, for example), it's likely that the whole /pramfs/configs/ directory will be corrupt, because the rename is writing to the directory inode, so you lose access to all names in that directory? That sounds like it can't be used for persistent configuration data. It's true from this point of view currently there is a lack for this and it needs a bit of effort to resolve this problem. From this point of view I'd like to point out that I know that there was some aspects to study in a deeper way, so I'll need of more then one review :) but since this fs has been abandoned since 2004 and it hadn't ever reviewed, it was important to do a serious review with the kernel community to understand all the problems. That's reasonable. What do you think of my suggestion to double-buffer writes using a single fixed position block, as explained elsewhere in this thread? It should give the power fail safety with very little code. I don't know how much it would slwo down writing. That probably depends on whether it's the checksum which is slow (which only needs to be done once when double-buffering), or the writing. Yeah it can be a choice. For this fs it's important to use simple but useful mechanism. What do you exactly mean with fixed position block? A fixed position in the fs? For example superblock+inodetable+in-use bitmap+blocks+double-buffering block? Using a temp block of the same size of blocks used, isn't it? I agree, but I think it needs more then 100 lines of code. Even with this simple schema it needs a mechanism with a timeout to do the commit of the temp block, it needs a mechanism to read the temp block instead of the old block or a mechanism to write-back the temp block. So it can be implemented but it needs a bit of effort. I think I'll implement it in the next release. I think you should really use ext3 over special block device. Initially this filesystem was presented as fast (it is not) then you claim it is reliable (it is not). If you want it to get reliable you'll need journalling+fsck. Good luck. Pavel -- (english) http://www.livejournal.com/~pavelmachek (cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html -- To unsubscribe from this list: send the line unsubscribe linux-embedded in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: [PATCH 00/14] Pramfs: Persistent and protected ram filesystem
Marco Stornelli wrote: 2009/6/24 Jamie Lokier ja...@shareable.org: Marco wrote: Second question: what happens if the system crashing _during_ a write to a file. Does it mean that file will fail it's checksum when it's read at the next boot? Maybe files aren't so important. What about when you write a file, and then rename it over an existing file to replace it. (E.g. a config file), and the system crashes _during_ the rename? At the next boot, is it guaranteed to see either the old or the new file, or can the directory be corrupt / fail it's checksum? First of all I have to explain better the current policy: the checksum works at inode and superblock level and currently there isn't a recovery function as the journaling. About the superblock it's easy to use a redundant policy to be more robust. To be honest, superblock robustness is less of a concern. The real concern is losing file or directory contents, so it can't be used to store persistent configuration data, only debugging logs. About the inode, at the moment when the checksum doesn't match the inode it's marked as bad calling the function make_bad_inode(). Let's see if I understand right. If it lose power when writing to a file, after boot the file is likely to be marked bad and so return -EIO instead of any file contents? Depends on the checksum. If you lose power before the checksum update of the inode you'll have a bad inode and then an -EIO at the next access. If it loses power when doing atomic rename (to replace config files, for example), it's likely that the whole /pramfs/configs/ directory will be corrupt, because the rename is writing to the directory inode, so you lose access to all names in that directory? That sounds like it can't be used for persistent configuration data. It's true from this point of view currently there is a lack for this and it needs a bit of effort to resolve this problem. From this point of view I'd like to point out that I know that there was some aspects to study in a deeper way, so I'll need of more then one review :) but since this fs has been abandoned since 2004 and it hadn't ever reviewed, it was important to do a serious review with the kernel community to understand all the problems. That's reasonable. What do you think of my suggestion to double-buffer writes using a single fixed position block, as explained elsewhere in this thread? It should give the power fail safety with very little code. I don't know how much it would slwo down writing. That probably depends on whether it's the checksum which is slow (which only needs to be done once when double-buffering), or the writing. -- Jamie -- To unsubscribe from this list: send the line unsubscribe linux-embedded in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: [PATCH 00/14] Pramfs: Persistent and protected ram filesystem
2009/6/24 Pavel Machek pa...@ucw.cz: On Wed 2009-06-24 19:38:37, Marco wrote: Pavel Machek wrote: On Mon 2009-06-22 14:50:01, Tim Bird wrote: Pavel Machek wrote: block of fast non-volatile RAM that need to access data on it using a standard filesytem interface. Turns a block of fast RAM into 13MB/sec disk. Hmm. I believe you are better with ext2. Not if you want the RAM-based filesystem to persist over a kernel invocation. Yes, you'll need to code Persistent, RAM-based _block_device_. First of all I have to say that I'd like to update the site and make it clearer but at the moment it's not possible because I'm not the admin and I've already asked to the sourceforge support to have this possibility. About the comments: sincerely I don't understand the comments. We have *already* a fs that takes care to remap a piace of ram (ram, sram, nvram, etc.), takes care of caching problems, takes care of write Well, it looks pramfs design is confused. 13MB/sec shows that caching _is_ useful for pramfs. So...? caching problems means to avoid filesystem corruption, so dirty pages in the page cache are not allowed to be written back to the backing-store RAM. It's clear that there is a performance penalty. This penalty should be reduced by the access speed of the RAM, however the performance are not important for this special fs as Tim Bird said, so this question is not relevant for me. If this issue is not clear enough on the web site, I hope I can update the information in the future. You are talked about journaling. This schema works well for a disk, but what about a piece of ram? What about a crazy kernel that write in that area for a bug? Do you remember for example the e1000e bug? It's not I believe you need both journaling *and* write protection. How do you handle power fault while writing data? Pavel Ah now the write protection is a needed feature, in your previous comment you talked about why not use ext2/3... Marco Just for your information I tried the same test with pc in a virtual machine with 32MB of RAM: Version 1.03e --Sequential Output-- --Sequential Input- --Random- -Per Chr- --Block-- -Rewrite- -Per Chr- --Block-- --Seeks-- Machine Size:chnk K/sec %CP K/sec %CP K/sec %CP K/sec %CP K/sec %CP /sec %CP hostname 15M:1k 14156 99 128779 100 92240 100 11669 100 166242 99 80058 82 --Sequential Create-- Random Create -Create-- --Read--- -Delete-- -Create-- --Read--- -Delete-- files /sec %CP /sec %CP /sec %CP /sec %CP /sec %CP /sec %CP 4 2842 99 133506 104 45088 101 2787 99 79581 101 58212 102 These data are the proof of the importance of the environment, workload and so on when we talk about benchmark. Your consideration are really superficial. Unfortunately, your numbers are meaningless. I don't think so. Pavel (PCs should have cca 3GB/sec RAM transfer rates; and you demosstrated cca 166MB/sec read rate; disk is 80MB/sec, so that's too slow. If you want to prove your filesystem the filesystem is reasonably fast, compare it with ext2 on ramdisk.) This is the point. I don't want compare it with ext2 from performance point of view. This comparison makes no sense for me. I've done this test to prove that if you change environment you can change in a purposeful way the results. Marco -- To unsubscribe from this list: send the line unsubscribe linux-embedded in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: [PATCH 00/14] Pramfs: Persistent and protected ram filesystem
Pavel Machek wrote: On Mon 2009-06-22 14:50:01, Tim Bird wrote: Pavel Machek wrote: block of fast non-volatile RAM that need to access data on it using a standard filesytem interface. Turns a block of fast RAM into 13MB/sec disk. Hmm. I believe you are better with ext2. Not if you want the RAM-based filesystem to persist over a kernel invocation. Yes, you'll need to code Persistent, RAM-based _block_device_. First of all I have to say that I'd like to update the site and make it clearer but at the moment it's not possible because I'm not the admin and I've already asked to the sourceforge support to have this possibility. About the comments: sincerely I don't understand the comments. We have *already* a fs that takes care to remap a piace of ram (ram, sram, nvram, etc.), takes care of caching problems, takes care of write Well, it looks pramfs design is confused. 13MB/sec shows that caching _is_ useful for pramfs. So...? caching problems means to avoid filesystem corruption, so dirty pages in the page cache are not allowed to be written back to the backing-store RAM. It's clear that there is a performance penalty. This penalty should be reduced by the access speed of the RAM, however the performance are not important for this special fs as Tim Bird said, so this question is not relevant for me. If this issue is not clear enough on the web site, I hope I can update the information in the future. You are talked about journaling. This schema works well for a disk, but what about a piece of ram? What about a crazy kernel that write in that area for a bug? Do you remember for example the e1000e bug? It's not I believe you need both journaling *and* write protection. How do you handle power fault while writing data? Pavel Ah now the write protection is a needed feature, in your previous comment you talked about why not use ext2/3... Marco -- To unsubscribe from this list: send the line unsubscribe linux-embedded in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: [PATCH 00/14] Pramfs: Persistent and protected ram filesystem
Marco wrote: Second question: what happens if the system crashing _during_ a write to a file. Does it mean that file will fail it's checksum when it's read at the next boot? Maybe files aren't so important. What about when you write a file, and then rename it over an existing file to replace it. (E.g. a config file), and the system crashes _during_ the rename? At the next boot, is it guaranteed to see either the old or the new file, or can the directory be corrupt / fail it's checksum? First of all I have to explain better the current policy: the checksum works at inode and superblock level and currently there isn't a recovery function as the journaling. About the superblock it's easy to use a redundant policy to be more robust. To be honest, superblock robustness is less of a concern. The real concern is losing file or directory contents, so it can't be used to store persistent configuration data, only debugging logs. About the inode, at the moment when the checksum doesn't match the inode it's marked as bad calling the function make_bad_inode(). Let's see if I understand right. If it lose power when writing to a file, after boot the file is likely to be marked bad and so return -EIO instead of any file contents? If it loses power when doing atomic rename (to replace config files, for example), it's likely that the whole /pramfs/configs/ directory will be corrupt, because the rename is writing to the directory inode, so you lose access to all names in that directory? That sounds like it can't be used for persistent configuration data. If a directory is marked as bad, or a file-inode in it is marked bad, can you even rmdir it to clean up and start again? Thanks, -- Jamie -- To unsubscribe from this list: send the line unsubscribe linux-embedded in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: [PATCH 00/14] Pramfs: Persistent and protected ram filesystem
Pavel Machek wrote: On Mon 2009-06-22 14:50:01, Tim Bird wrote: Pavel Machek wrote: block of fast non-volatile RAM that need to access data on it using a standard filesytem interface. Turns a block of fast RAM into 13MB/sec disk. Hmm. I believe you are better with ext2. Not if you want the RAM-based filesystem to persist over a kernel invocation. Yes, you'll need to code Persistent, RAM-based _block_device_. First of all I have to say that I'd like to update the site and make it clearer but at the moment it's not possible because I'm not the admin and I've already asked to the sourceforge support to have this possibility. About the comments: sincerely I don't understand the comments. We have *already* a fs that takes care to remap a piace of ram (ram, sram, nvram, etc.), takes care of caching problems, takes care of write Well, it looks pramfs design is confused. 13MB/sec shows that caching _is_ useful for pramfs. So...? caching problems means to avoid filesystem corruption, so dirty pages in the page cache are not allowed to be written back to the backing-store RAM. It's clear that there is a performance penalty. This penalty should be reduced by the access speed of the RAM, however the performance are not important for this special fs as Tim Bird said, so this question is not relevant for me. If this issue is not clear enough on the web site, I hope I can update the information in the future. You are talked about journaling. This schema works well for a disk, but what about a piece of ram? What about a crazy kernel that write in that area for a bug? Do you remember for example the e1000e bug? It's not I believe you need both journaling *and* write protection. How do you handle power fault while writing data? Pavel Ah now the write protection is a needed feature, in your previous comment you talked about why not use ext2/3... Marco Just for your information I tried the same test with pc in a virtual machine with 32MB of RAM: Version 1.03e --Sequential Output-- --Sequential Input- --Random- -Per Chr- --Block-- -Rewrite- -Per Chr- --Block-- --Seeks-- Machine Size:chnk K/sec %CP K/sec %CP K/sec %CP K/sec %CP K/sec %CP /sec %CP hostname 15M:1k 14156 99 128779 100 92240 100 11669 100 166242 99 80058 82 --Sequential Create-- Random Create -Create-- --Read--- -Delete-- -Create-- --Read--- -Delete-- files /sec %CP /sec %CP /sec %CP /sec %CP /sec %CP /sec %CP 4 2842 99 133506 104 45088 101 2787 99 79581 101 58212 102 These data are the proof of the importance of the environment, workload and so on when we talk about benchmark. Your consideration are really superficial. Marco -- To unsubscribe from this list: send the line unsubscribe linux-embedded in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: [PATCH 00/14] Pramfs: Persistent and protected ram filesystem
Pavel Machek wrote: On Tue 2009-06-23 20:07:23, Marco wrote: You are talked about journaling. This schema works well for a disk, but what about a piece of ram? What about a crazy kernel that write in that area for a bug? Do you remember for example the e1000e bug? It's not I believe you need both journaling *and* write protection. How do you handle power fault while writing data? I think this is basically right. write protection for the crazy kernels, and journalling for powerfail/crash during updates. Journalling can be extremely simple. It can be just one memory block at a fixed location, double-buffering all writes. Pramfs already has checksums, which makes that easier. You just write to the buffer area first, with checksum, then write to the final area. Mount looks at the buffer area, and if the checksum is fine, copies the contents to the destination block. That's all it takes to be resistant against power failures and crashes during writes. Probably 100 lines of code. -- Jamie -- To unsubscribe from this list: send the line unsubscribe linux-embedded in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: [PATCH 00/14] Pramfs: Persistent and protected ram filesystem
On Wed 2009-06-24 18:49:11, Marco wrote: Pavel Machek wrote: On Mon 2009-06-22 14:50:01, Tim Bird wrote: Pavel Machek wrote: block of fast non-volatile RAM that need to access data on it using a standard filesytem interface. Turns a block of fast RAM into 13MB/sec disk. Hmm. I believe you are better with ext2. Not if you want the RAM-based filesystem to persist over a kernel invocation. Yes, you'll need to code Persistent, RAM-based _block_device_. First of all I have to say that I'd like to update the site and make it clearer but at the moment it's not possible because I'm not the admin and I've already asked to the sourceforge support to have this possibility. About the comments: sincerely I don't understand the comments. We have *already* a fs that takes care to remap a piace of ram (ram, sram, nvram, etc.), takes care of caching problems, takes care of write Well, it looks pramfs design is confused. 13MB/sec shows that caching _is_ useful for pramfs. So...? caching problems means to avoid filesystem corruption, so dirty pages in the page cache are not allowed to be written back to the backing-store RAM. It's clear that there is a performance penalty. This penalty should be reduced by the access speed of the RAM, however the performance are not important for this special fs as Tim Bird said, so this question is not relevant for me. If this issue is not clear enough on the web site, I hope I can update the information in the future. Yes, please update the pages... You are talked about journaling. This schema works well for a disk, but what about a piece of ram? What about a crazy kernel that write in that area for a bug? Do you remember for example the e1000e bug? It's not I believe you need both journaling *and* write protection. How do you handle power fault while writing data? Ah now the write protection is a needed feature, in your previous comment you talked about why not use ext2/3... write protection should be handled at block device layer, not filesystem layer. So yes, use ext2. You still did not explain how you avoid the need for journalling... Pavel -- (english) http://www.livejournal.com/~pavelmachek (cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html -- To unsubscribe from this list: send the line unsubscribe linux-embedded in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: [PATCH 00/14] Pramfs: Persistent and protected ram filesystem
Pavel Machek wrote: On Mon 2009-06-22 14:50:01, Tim Bird wrote: Pavel Machek wrote: block of fast non-volatile RAM that need to access data on it using a standard filesytem interface. Turns a block of fast RAM into 13MB/sec disk. Hmm. I believe you are better with ext2. Not if you want the RAM-based filesystem to persist over a kernel invocation. Yes, you'll need to code Persistent, RAM-based _block_device_. Pavel First of all I have to say that I'd like to update the site and make it clearer but at the moment it's not possible because I'm not the admin and I've already asked to the sourceforge support to have this possibility. About the comments: sincerely I don't understand the comments. We have *already* a fs that takes care to remap a piace of ram (ram, sram, nvram, etc.), takes care of caching problems, takes care of write protection, takes care to be persistent, can use xip and it's my intention to add in the next future other features like acl, xattr and so on. You are talked about journaling. This schema works well for a disk, but what about a piece of ram? What about a crazy kernel that write in that area for a bug? Do you remember for example the e1000e bug? It's not casual that this fs use an hw protection schema. I mean, this fs is not only a yet another fs, but a fs born with a specific target. So I think modifying a ramdisk to have these behaviors isn't a little modification. Marco -- To unsubscribe from this list: send the line unsubscribe linux-embedded in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: [PATCH 00/14] Pramfs: Persistent and protected ram filesystem
On Tue 2009-06-23 20:07:23, Marco wrote: Pavel Machek wrote: On Mon 2009-06-22 14:50:01, Tim Bird wrote: Pavel Machek wrote: block of fast non-volatile RAM that need to access data on it using a standard filesytem interface. Turns a block of fast RAM into 13MB/sec disk. Hmm. I believe you are better with ext2. Not if you want the RAM-based filesystem to persist over a kernel invocation. Yes, you'll need to code Persistent, RAM-based _block_device_. First of all I have to say that I'd like to update the site and make it clearer but at the moment it's not possible because I'm not the admin and I've already asked to the sourceforge support to have this possibility. About the comments: sincerely I don't understand the comments. We have *already* a fs that takes care to remap a piace of ram (ram, sram, nvram, etc.), takes care of caching problems, takes care of write Well, it looks pramfs design is confused. 13MB/sec shows that caching _is_ useful for pramfs. So...? You are talked about journaling. This schema works well for a disk, but what about a piece of ram? What about a crazy kernel that write in that area for a bug? Do you remember for example the e1000e bug? It's not I believe you need both journaling *and* write protection. How do you handle power fault while writing data? Pavel -- (english) http://www.livejournal.com/~pavelmachek (cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html -- To unsubscribe from this list: send the line unsubscribe linux-embedded in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: [PATCH 00/14] Pramfs: Persistent and protected ram filesystem
How do you handle hard-links, then? Indeed hard-links are not supported :) Due to the design of this fs there are some limitations explained in the documentation as not hard-link, only private memory mapping and so on. However this limitations don't limit the fs itself because you must consider the special goal of this fs. I did not see that in the changelog. If it is not general purpose filesystem, it is lot less interesting. From performance point of view: Sometimes ago I uploaded here (http://elinux.org/Pram_Fs) some benchmark results to compare the performance with and without XIP in a real embedded environment with bonnie++. You could use it as reference point. Well, so XIP helps. ext2 can do XIP too, IIRC. Is your performance better than ext2? Wait... those numbers you pointed me... claim to be as slow as 13MB/sec. That's very very bad. My harddrive is faster than that. As I said I did the test in a real embedded environment so to have comparable result you should use the same environmente with the same tools, with the same workload and so on. Even on real embedded hardware you should get better than 13MB/sec writing to _RAM_. I guess something is seriously wrong with pramfs. Pavel -- (english) http://www.livejournal.com/~pavelmachek (cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html -- To unsubscribe from this list: send the line unsubscribe linux-embedded in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: [PATCH 00/14] Pramfs: Persistent and protected ram filesystem
Pavel Machek wrote: How do you handle hard-links, then? Indeed hard-links are not supported :) Due to the design of this fs there are some limitations explained in the documentation as not hard-link, only private memory mapping and so on. However this limitations don't limit the fs itself because you must consider the special goal of this fs. I did not see that in the changelog. If it is not general purpose filesystem, it is lot less interesting. PRAMFS is not a general purpose filesystem. Please read the introductory post to this thread, or look at http://pramfs.sourceforge.net/ for more information. Since the purpose of PRAMFS is to provide a filesystem that is persistent across kernel instantions, it is not designed for high speed. Robustness in the face of kernel crashes or bugs is the highest priority, so PRAMFS has significant overhead to make the window of writability to the filesystem RAM as small as possible. This is not a file system one would do kernel compiles on. This is where someone would keep a small amount of sensitive data, or crash logs that one needed to preserve over kernel invocations. From performance point of view: Sometimes ago I uploaded here (http://elinux.org/Pram_Fs) some benchmark results to compare the performance with and without XIP in a real embedded environment with bonnie++. You could use it as reference point. Well, so XIP helps. ext2 can do XIP too, IIRC. Is your performance better than ext2? Wait... those numbers you pointed me... claim to be as slow as 13MB/sec. That's very very bad. My harddrive is faster than that. As I said I did the test in a real embedded environment so to have comparable result you should use the same environmente with the same tools, with the same workload and so on. Even on real embedded hardware you should get better than 13MB/sec writing to _RAM_. I guess something is seriously wrong with pramfs. See above. = Tim Bird Architecture Group Chair, CE Linux Forum Senior Staff Engineer, Sony Corporation of America = -- To unsubscribe from this list: send the line unsubscribe linux-embedded in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: [PATCH 00/14] Pramfs: Persistent and protected ram filesystem
On Mon 2009-06-22 10:31:28, Tim Bird wrote: Pavel Machek wrote: How do you handle hard-links, then? Indeed hard-links are not supported :) Due to the design of this fs there are some limitations explained in the documentation as not hard-link, only private memory mapping and so on. However this limitations don't limit the fs itself because you must consider the special goal of this fs. I did not see that in the changelog. If it is not general purpose filesystem, it is lot less interesting. PRAMFS is not a general purpose filesystem. Please read the introductory post to this thread, or look at http://pramfs.sourceforge.net/ for more information. Yeah, I seen that. It directly contradicts what you say. Since the purpose of PRAMFS is to provide a filesystem that is persistent across kernel instantions, it is not designed for high speed. Robustness in the face of kernel crashes or bugs is the highest priority, so PRAMFS has significant overhead to make the window of writability to the filesystem RAM as small as possible. Really? So why don't you use well known, reliable fs like ext3? This is not a file system one would do kernel compiles on. This is where someone would keep a small amount of sensitive data, or crash logs that one needed to preserve over kernel invocations. Really? Web page says: #2. If the backing-store RAM is comparable in access speed to system #memory, there's really no point in caching the file I/O data in the #page cache. Better to move file data directly between the user buffers #and the backing store RAM, i.e. use direct I/O. This prevents the #unnecessary So you don't cache it because its fast, and then it is 13MB/sec? Pavel -- (english) http://www.livejournal.com/~pavelmachek (cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html -- To unsubscribe from this list: send the line unsubscribe linux-embedded in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: [PATCH 00/14] Pramfs: Persistent and protected ram filesystem
Pavel Machek wrote: On Mon 2009-06-22 10:31:28, Tim Bird wrote: Pavel Machek wrote: How do you handle hard-links, then? Indeed hard-links are not supported :) Due to the design of this fs there are some limitations explained in the documentation as not hard-link, only private memory mapping and so on. However this limitations don't limit the fs itself because you must consider the special goal of this fs. I did not see that in the changelog. If it is not general purpose filesystem, it is lot less interesting. PRAMFS is not a general purpose filesystem. Please read the introductory post to this thread, or look at http://pramfs.sourceforge.net/ for more information. Yeah, I seen that. It directly contradicts what you say. I don't think, I think it's very clear: In summary, PRAMFS is a light-weight, full-featured, and space-efficient special filesystem that is ideal for systems with a block of fast non-volatile RAM that need to access data on it using a standard filesytem interface. Since the purpose of PRAMFS is to provide a filesystem that is persistent across kernel instantions, it is not designed for high speed. Robustness in the face of kernel crashes or bugs is the highest priority, so PRAMFS has significant overhead to make the window of writability to the filesystem RAM as small as possible. Really? So why don't you use well known, reliable fs like ext3? This is not a file system one would do kernel compiles on. This is where someone would keep a small amount of sensitive data, or crash logs that one needed to preserve over kernel invocations. Really? Web page says: #2. If the backing-store RAM is comparable in access speed to system #memory, there's really no point in caching the file I/O data in the #page cache. Better to move file data directly between the user buffers #and the backing store RAM, i.e. use direct I/O. This prevents the #unnecessary So you don't cache it because its fast, and then it is 13MB/sec? Pavel -- To unsubscribe from this list: send the line unsubscribe linux-embedded in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: [PATCH 00/14] Pramfs: Persistent and protected ram filesystem
Pavel Machek wrote: On Mon 2009-06-22 10:31:28, Tim Bird wrote: Pavel Machek wrote: I did not see that in the changelog. If it is not general purpose filesystem, it is lot less interesting. PRAMFS is not a general purpose filesystem. Please read the introductory post to this thread, or look at http://pramfs.sourceforge.net/ for more information. Yeah, I seen that. It directly contradicts what you say. Could you be more specific? In what way does the description on the website contradict what I said? Since the purpose of PRAMFS is to provide a filesystem that is persistent across kernel instantions, it is not designed for high speed. Robustness in the face of kernel crashes or bugs is the highest priority, so PRAMFS has significant overhead to make the window of writability to the filesystem RAM as small as possible. Really? So why don't you use well known, reliable fs like ext3? Are you sure you read the web site? It directly addresses this question. From the web site: 1. Disk-based filesystems such as ext2/ext3 were designed for optimum performance on spinning disk media, so they implement features such as block groups, which attempts to group inode data into a contiguous set of data blocks to minimize disk seeking when accessing files. For RAM there is no such concern; a file's data blocks can be scattered throughout the media with no access speed penalty at all. So block groups in a filesystem mounted over RAM just adds unnecessary complexity. A better approach is to use a filesystem specifically tailored to RAM media which does away with these disk-based features. This increases the efficient use of space on the media, i.e. more space is dedicated to actual file data storage and less to meta-data needed to maintain that file data. This is not a file system one would do kernel compiles on. This is where someone would keep a small amount of sensitive data, or crash logs that one needed to preserve over kernel invocations. Really? Web page says: #2. If the backing-store RAM is comparable in access speed to system #memory, there's really no point in caching the file I/O data in the #page cache. Better to move file data directly between the user buffers #and the backing store RAM, i.e. use direct I/O. This prevents the #unnecessary So you don't cache it because its fast, and then it is 13MB/sec? I'm not sure what you're quoting. The paragraph you quoted doesn't have the words because its fast [sic]. Speed is not a primary consideration for this filesystem. Due to the overhead of changing the page flags, it's possible that using the page cache would speed up overall access to this filesystem. (This would depend on the cost of changing the access flags, and the pattern of operations on the filesystem.) However, using the page cache would add a level of indirection which would detract from the intended robustness. -- Tim = Tim Bird Architecture Group Chair, CE Linux Forum Senior Staff Engineer, Sony Corporation of America = -- To unsubscribe from this list: send the line unsubscribe linux-embedded in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: [PATCH 00/14] Pramfs: Persistent and protected ram filesystem
On Mon, 22 Jun 2009, Marco wrote: I don't think, I think it's very clear: In summary, PRAMFS is a light-weight, full-featured, and space-efficient special filesystem that is ideal for systems with a block of fast non-volatile RAM that need to access data on it using a standard filesytem interface. It is not full-featured if it doesn't have support for hardlinks, security labels, extended attributes, etc. Please call it a specialized filesystem instead, that seems to be much more in line with the comments about pramfs use cases in this thread... Oh, and that should be in the Kconfig help text, as well as the stuff that goes in Documentation/*, obviously. Maybe it already is, I didn't look. -- One disk to rule them all, One disk to find them. One disk to bring them all and in the darkness grind them. In the Land of Redmond where the shadows lie. -- The Silicon Valley Tarot Henrique Holschuh -- To unsubscribe from this list: send the line unsubscribe linux-embedded in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: [PATCH 00/14] Pramfs: Persistent and protected ram filesystem
On Mon 2009-06-22 20:07:06, Marco wrote: Pavel Machek wrote: On Mon 2009-06-22 10:31:28, Tim Bird wrote: Pavel Machek wrote: How do you handle hard-links, then? Indeed hard-links are not supported :) Due to the design of this fs there are some limitations explained in the documentation as not hard-link, only private memory mapping and so on. However this limitations don't limit the fs itself because you must consider the special goal of this fs. I did not see that in the changelog. If it is not general purpose filesystem, it is lot less interesting. PRAMFS is not a general purpose filesystem. Please read the introductory post to this thread, or look at http://pramfs.sourceforge.net/ for more information. Yeah, I seen that. It directly contradicts what you say. I don't think, I think it's very clear: In summary, PRAMFS is a light-weight, full-featured, and space-efficient special filesystem that is ideal for systems with a Except that it is not full-featured. No hardlinks. (What about ACLs, etc?) block of fast non-volatile RAM that need to access data on it using a standard filesytem interface. Turns a block of fast RAM into 13MB/sec disk. Hmm. I believe you are better with ext2. -- (english) http://www.livejournal.com/~pavelmachek (cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html -- To unsubscribe from this list: send the line unsubscribe linux-embedded in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: [PATCH 00/14] Pramfs: Persistent and protected ram filesystem
On Mon 2009-06-22 11:55:04, Tim Bird wrote: Pavel Machek wrote: On Mon 2009-06-22 10:31:28, Tim Bird wrote: Pavel Machek wrote: I did not see that in the changelog. If it is not general purpose filesystem, it is lot less interesting. PRAMFS is not a general purpose filesystem. Please read the introductory post to this thread, or look at http://pramfs.sourceforge.net/ for more information. Yeah, I seen that. It directly contradicts what you say. Could you be more specific? In what way does the description on the website contradict what I said? You are saying top goal is robustness, while the web page says (home page, stop using frames!): embedded systems have a block of non-volatile RAM seperate from normal system memory, i.e. of which the kernel maintains no memory page descriptors. For such systems it would be beneficial to mount a fast read/write filesystem over this I/O memory, for storing frequently accessed data that must survive system reboots and power cycles Note the frequently accessed and fast. IOW the web page is confusing. It does not talk about robustness at all. Since the purpose of PRAMFS is to provide a filesystem that is persistent across kernel instantions, it is not designed for high speed. Robustness in the face of kernel crashes or bugs is the highest priority, so PRAMFS has significant overhead to make the window of writability to the filesystem RAM as small as possible. Really? So why don't you use well known, reliable fs like ext3? Are you sure you read the web site? It directly addresses this question. From the web site: 1. Disk-based filesystems such as No, it does not. It explains that ext2 would be too slow on this, and explains that it will eat too much disk space. Please back that claims with numbers. If reliability is top concern, explain how you get away w/o journalling. Pavel -- (english) http://www.livejournal.com/~pavelmachek (cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html -- To unsubscribe from this list: send the line unsubscribe linux-embedded in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: [PATCH 00/14] Pramfs: Persistent and protected ram filesystem
On Mon 2009-06-22 14:50:01, Tim Bird wrote: Pavel Machek wrote: block of fast non-volatile RAM that need to access data on it using a standard filesytem interface. Turns a block of fast RAM into 13MB/sec disk. Hmm. I believe you are better with ext2. Not if you want the RAM-based filesystem to persist over a kernel invocation. Yes, you'll need to code Persistent, RAM-based _block_device_. Pavel -- (english) http://www.livejournal.com/~pavelmachek (cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html -- To unsubscribe from this list: send the line unsubscribe linux-embedded in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: [PATCH 00/14] Pramfs: Persistent and protected ram filesystem
On Mon 2009-06-22 23:57:53, Pavel Machek wrote: On Mon 2009-06-22 14:50:01, Tim Bird wrote: Pavel Machek wrote: block of fast non-volatile RAM that need to access data on it using a standard filesytem interface. Turns a block of fast RAM into 13MB/sec disk. Hmm. I believe you are better with ext2. Not if you want the RAM-based filesystem to persist over a kernel invocation. Yes, you'll need to code Persistent, RAM-based _block_device_. More politely said: I believe you would be better off modifying ramdisk to include the functionality for persistence. New filesystem should not really be neccessary. ext2 for performance, ext3 if you need robustness from journalling, maybe something else makes sense, too. Pavel -- (english) http://www.livejournal.com/~pavelmachek (cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html -- To unsubscribe from this list: send the line unsubscribe linux-embedded in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: [PATCH 00/14] Pramfs: Persistent and protected ram filesystem
Why is an entire filesystem needed, instead of simply a block driver if the ramdisk driver cannot be used? From documentation: A relatively straight-forward solution is to write a simple block driver for the non-volatile RAM, and mount over it any disk-based filesystem such as ext2/ext3, reiserfs, etc. But the disk-based fs over non-volatile RAM block driver approach has some drawbacks: 1. Disk-based filesystems such as ext2/ext3 were designed for optimum performance on spinning disk media, so they implement features such as block groups, which attempts to group inode data into a contiguous set of data blocks to minimize disk seeking when accessing files. For RAM there is no such concern; a file's data blocks can be scattered throughout the media with no access speed penalty at all. So block groups in a filesystem mounted over RAM just adds unnecessary complexity. A better approach is to use a filesystem specifically tailored to RAM media which does away with these disk-based features. This increases the efficient use of space on the media, i.e. more space is dedicated to actual file data storage and less to meta-data needed to maintain that file data. So... what is the performance difference between ext2 and your new filesystem? -- (english) http://www.livejournal.com/~pavelmachek (cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html -- To unsubscribe from this list: send the line unsubscribe linux-embedded in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: [PATCH 00/14] Pramfs: Persistent and protected ram filesystem
Pavel Machek wrote: Why is an entire filesystem needed, instead of simply a block driver if the ramdisk driver cannot be used? From documentation: A relatively straight-forward solution is to write a simple block driver for the non-volatile RAM, and mount over it any disk-based filesystem such as ext2/ext3, reiserfs, etc. But the disk-based fs over non-volatile RAM block driver approach has some drawbacks: 1. Disk-based filesystems such as ext2/ext3 were designed for optimum performance on spinning disk media, so they implement features such as block groups, which attempts to group inode data into a contiguous set of data blocks to minimize disk seeking when accessing files. For RAM there is no such concern; a file's data blocks can be scattered throughout the media with no access speed penalty at all. So block groups in a filesystem mounted over RAM just adds unnecessary complexity. A better approach is to use a filesystem specifically tailored to RAM media which does away with these disk-based features. This increases the efficient use of space on the media, i.e. more space is dedicated to actual file data storage and less to meta-data needed to maintain that file data. So... what is the performance difference between ext2 and your new filesystem? About the space you can read a detailed documentation on the site: http://pramfs.sourceforge.net/pramfs-spec.html In addition I can do an example of compact information: ext2 uses directory entry objects (dentries) to associate file names to inodes, and these dentries are located in data blocks owned by the parent directory. In pramfs, directory inode's do not need to own any data blocks, because all dentry information is contained within the inode's themselves. From performance point of view: Sometimes ago I uploaded here (http://elinux.org/Pram_Fs) some benchmark results to compare the performance with and without XIP in a real embedded environment with bonnie++. You could use it as reference point. I hope I've answered to your question. Regards, Marco -- To unsubscribe from this list: send the line unsubscribe linux-embedded in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: [PATCH 00/14] Pramfs: Persistent and protected ram filesystem
1. Disk-based filesystems such as ext2/ext3 were designed for optimum performance on spinning disk media, so they implement features such as block groups, which attempts to group inode data into a contiguous set of data blocks to minimize disk seeking when accessing files. For RAM there is no such concern; a file's data blocks can be scattered throughout the media with no access speed penalty at all. So block groups in a filesystem mounted over RAM just adds unnecessary complexity. A better approach is to use a filesystem specifically tailored to RAM media which does away with these disk-based features. This increases the efficient use of space on the media, i.e. more space is dedicated to actual file data storage and less to meta-data needed to maintain that file data. So... what is the performance difference between ext2 and your new filesystem? About the space you can read a detailed documentation on the site: http://pramfs.sourceforge.net/pramfs-spec.html I do not see any numbers there. Do you think you can save significant memory when storing for example kernel source trees? In addition I can do an example of compact information: ext2 uses directory entry objects (dentries) to associate file names to inodes, I'm not sure that on-disk directory entry == dentry. and these dentries are located in data blocks owned by the parent directory. In pramfs, directory inode's do not need to own any data blocks, because all dentry information is contained within the inode's themselves. How do you handle hard-links, then? From performance point of view: Sometimes ago I uploaded here (http://elinux.org/Pram_Fs) some benchmark results to compare the performance with and without XIP in a real embedded environment with bonnie++. You could use it as reference point. Well, so XIP helps. ext2 can do XIP too, IIRC. Is your performance better than ext2? Wait... those numbers you pointed me... claim to be as slow as 13MB/sec. That's very very bad. My harddrive is faster than that. Pavel -- (english) http://www.livejournal.com/~pavelmachek (cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html -- To unsubscribe from this list: send the line unsubscribe linux-embedded in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: [PATCH 00/14] Pramfs: Persistent and protected ram filesystem
2009/6/17 Chris Friesen cfrie...@nortel.com: Marco wrote: This is a second attempt at mainlining Pramfs. The first attempt was back in early 2004 by MontaVista. Since then the kernel code has almost been completely rewritten. So my first item on the list was porting the code on a recent kernel version. After that I added the XIP support. Now some FAQs: What is the goal of this filesystem? Many embedded systems have a block of non-volatile RAM separate from normal system memory, i.e. of which the kernel maintains no memory page descriptors. For such systems it would be beneficial to mount a fast read/write filesystem over this I/O memory, for storing frequently accessed data that must survive system reboots and power cycles. An example usage might be system logs under /var/log, or a user address book in a cell phone or PDA. Nice to see something like this submitted to mainline. We use something similar to provide persistent storage for crash recovery debug data for boards which don't have local storage. In many cases kdump can provide good information, but it's not sufficient for flight recorder type data if the kernel gets rebooted by a hardware mechanism (watchdog, for instance) that doesn't give a pre-interrupt. I'm very happy that this fs has the approval of the kernel community. :) I'm a bit concerned about your PTE modifications on every write though...we do things like log every exception and scheduler operation to persistent memory, and I think the overhead of changing the protection on every write would be a killer. Instead, we make extensive use of checksums at various different levels so that the recovery app can determine which data is valid. It's a trade-off between security and performance. Checksum it's a good way to understand if a data is valid or not (indeed it's used in this fs), but with this schema you can prevent the system to do something wrong. This option, however, can be enabled/disabled via kconfig. Also, I'd like to ensure that direct memory access to the memory area would be available. What do you exactly mean with this? Can you explain to me a bit deeper? There are some things (like the sched/exception logging mentioned above) where we want to make accesses as fast as possible. Chris Marco -- To unsubscribe from this list: send the line unsubscribe linux-embedded in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: [PATCH 00/14] Pramfs: Persistent and protected ram filesystem
Marco wrote: There's the checksum, but the most important feature of this fs is the write protection. The page table entries that map the backing-store RAM are normally marked read-only. Write operations into the filesystem temporarily mark the affected pages as writeable, the write operation is carried out with locks held, and then the pte is marked read-only again. This feature provides protection against filesystem corruption caused by errant writes into the RAM due to kernel bugs for instance. I provided a test module for this. When the module is loaded tries to do a dirty write in the superblock, at this point you should see an error on the write. Ok. Random question: does it work with NOMMU? :-) (I'm biased, my devices are NOMMU). Second question: what happens if the system crashing _during_ a write to a file. Does it mean that file will fail it's checksum when it's read at the next boot? Maybe files aren't so important. What about when you write a file, and then rename it over an existing file to replace it. (E.g. a config file), and the system crashes _during_ the rename? At the next boot, is it guaranteed to see either the old or the new file, or can the directory be corrupt / fail it's checksum? As you say PRAMFS can work with special SRAMs needing memory protection (and maybe cache coherence?), if you mmap() a file does it need to use the page cache then? If so, do you have issues with coherency between mmap() and direct read/write? See my response above about my concept of protection. However the mmap it's a similar approach. I can mmap the SRAM and I can write into it my data, but I think the possibility to have a fs it's great. We can use the device as normal disk, i.e. we can use cp, mv and so on. I meant when you mmap() a file on the filesystem, like you do when running an executable, for example. Does mmap() on a file work or is it forbidden? Just curious, I'd guess it's forbidden, and you wouldn't want _direct_ mappings to the backing SRAM anyway so you can keep those checksums up to date. On this point I'd like to hear other embedded guys. As one, I'd like to say if it can checksum the RAM at boot as well, then I might like to use a small one in ordinary SRAM (at a fixed reserved address) for those occasions when a reboot happens (intentional or not) and I'd like to pass a little data to the next running kernel about why the reboot happened, without touching flash every time. -- Jamie Yeah Jamie, the goal of this fs is exactly that! Great :-) -- Jamie -- To unsubscribe from this list: send the line unsubscribe linux-embedded in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: [PATCH 00/14] Pramfs: Persistent and protected ram filesystem
Marco wrote: To enable direct I/O at all times for all regular files requires either that applications be modified to include the O_DIRECT flag on all file opens, or that a new filesystem be used that always performs direct I/O by default. This could be done as well by just introducing a direct_io_only mount option to a file-system which would need this feature. A mount option would not be the right way. Mount options are for things that are characteristic of the way you're going to access the files. _This_ is a characteristic of the block device. So if one were to make this memory accessible with a block device, it would make more sense to have a block device ioctl. And it wouldn't ask the question, should I use direct I/O only, but does this device have the performance characteristics of a classic disk drive? But it's possible that there's just no advantage to having a block device in the stack here. When unix block devices were invented, their main purpose was that they could reorder reads and writes and do buffering and caching -- all things essential for disk drives. We don't want to stretch the concept too far. -- Bryan Henderson IBM Almaden Research Center San Jose CA Storage Systems -- To unsubscribe from this list: send the line unsubscribe linux-embedded in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: [PATCH 00/14] Pramfs: Persistent and protected ram filesystem
Bryan Henderson wrote: Marco wrote: To enable direct I/O at all times for all regular files requires either that applications be modified to include the O_DIRECT flag on all file opens, or that a new filesystem be used that always performs direct I/O by default. This could be done as well by just introducing a direct_io_only mount option to a file-system which would need this feature. But it's possible that there's just no advantage to having a block device in the stack here. When unix block devices were invented, their main purpose was that they could reorder reads and writes and do buffering and caching -- all things essential for disk drives. We don't want to stretch the concept too far. Yes I agree, we can't in this case talk about read and write reordering, buffering and caching because we're talking about something completely different from a classic disk. The issues of this kind of fs are more similar to the tmpfs issues. Marco -- To unsubscribe from this list: send the line unsubscribe linux-embedded in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: [PATCH 00/14] Pramfs: Persistent and protected ram filesystem
Tim Bird wrote: Marco wrote: This is a second attempt at mainlining Pramfs. The first attempt was back in early 2004 by MontaVista. Since then the kernel code has almost been completely rewritten. So my first item on the list was porting the code on a recent kernel version. After that I added the XIP support. It's very nice to see this technology revived. Is the information at: http://pramfs.sourceforge.net/ and http://pramfs.sourceforge.net/pramfs-spec.html still valid - particularly the latter? Yep. at 99%. I've done some modifications due to the porting and there will be some ones due to this review. I tried to talk with Steve Longerbeam to update the site but without success. I'd like to update it. It would be very nice to see this get mainlined. I believe that one of the main uses for this is to store crash information over a reboot so the next kernel (not in crashing state) can have a better chance of dealing with it. As such, I think it's important to keep the code paths for Pramfs short, synchronous, and unentangled with other kernel systems (block IO, page cache, etc.). Yes, I quite agree. I think that this kind of feature would be very useful especially for the embedded world. Marco -- To unsubscribe from this list: send the line unsubscribe linux-embedded in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: [PATCH 00/14] Pramfs: Persistent and protected ram filesystem
Marco wrote: To enable direct I/O at all times for all regular files requires either that applications be modified to include the O_DIRECT flag on all file opens, or that a new filesystem be used that always performs direct I/O by default. This could be done as well by just introducing a direct_io_only mount option to a file-system which would need this feature. -- Best Regards, Artem Bityutskiy (Артём Битюцкий) -- To unsubscribe from this list: send the line unsubscribe linux-embedded in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: [PATCH 00/14] Pramfs: Persistent and protected ram filesystem
Marco wrote: Simply because the ramdisk was not designed to work in a persistent environment. One thing with persistent RAM disks is you _really_ want it to be robust if the system crashes for any reason while it is being modified. The last thing you want is to reboot, and find various directories containing configuration files or application files have been corrupted or disappeared as a side effect of writing something else. That's one of the advantages of using a log-structured filesystem such as Nilfs, JFFS2, Logfs, UBIFS, Btrfs, ext3, reiserfs, XFS or JFS on a ramdisk :-) Does PRAMFS have this kind of robustness? In addition this kind of filesystem has been designed to work not only with classic ram. You can think at the situation where you have got an external SRAM with a battery for example. With it you can remap in an easy way the SRAM. Moreover there's the issue of memory protection that this filesystem takes care. Why is an entire filesystem needed, instead of simply a block driver if the ramdisk driver cannot be used? From documentation: A relatively straight-forward solution is to write a simple block driver for the non-volatile RAM, and mount over it any disk-based filesystem such as ext2/ext3, reiserfs, etc. But the disk-based fs over non-volatile RAM block driver approach has some drawbacks: 1. Disk-based filesystems such as ext2/ext3 were designed for optimum performance on spinning disk media, so they implement features such as block groups, which attempts to group inode data into a contiguous set of data blocks to minimize disk seeking when accessing files. For RAM there is no such concern; a file's data blocks can be scattered throughout the media with no access speed penalty at all. So block groups in a filesystem mounted over RAM just adds unnecessary complexity. A better approach is to use a filesystem specifically tailored to RAM media which does away with these disk-based features. This increases the efficient use of space on the media, i.e. more space is dedicated to actual file data storage and less to meta-data needed to maintain that file data. All true, I agree. RAM-based databases use different structures to disk-based databases for the same reasons. Isn't there any good RAM-based filesystem already? Some of the flash filesystems and Nilfs seem promising, using fake MTD with a small erase size. All are robust on crashes. 2. If the backing-store RAM is comparable in access speed to system memory, there's really no point in caching the file I/O data in the page cache. Better to move file data directly between the user buffers and the backing store RAM, i.e. use direct I/O. This prevents the unnecessary populating of the page cache with dirty pages. Good idea. However direct I/O has to be enabled at every file open. To enable direct I/O at all times for all regular files requires either that applications be modified to include the O_DIRECT flag on all file opens, or that a new filesystem be used that always performs direct I/O by default. There are other ways to include the O_DIRECT flag automatically. A generic mount option would be enough. I've seen other OSes with such an option. That code for that would be tiny. But standard O_DIRECT direct I/O doesn't work for all applications: it has to be aligned: device offset, application memory address and size all have to be aligned. (It would be a nice touch to produce a generic mount option o_direct_when_possible, which turns on direct I/O but permits unaligned I/O. That could be used with all applications.) As you say PRAMFS can work with special SRAMs needing memory protection (and maybe cache coherence?), if you mmap() a file does it need to use the page cache then? If so, do you have issues with coherency between mmap() and direct read/write? On this point I'd like to hear other embedded guys. As one, I'd like to say if it can checksum the RAM at boot as well, then I might like to use a small one in ordinary SRAM (at a fixed reserved address) for those occasions when a reboot happens (intentional or not) and I'd like to pass a little data to the next running kernel about why the reboot happened, without touching flash every time. -- Jamie -- To unsubscribe from this list: send the line unsubscribe linux-embedded in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: [PATCH 00/14] Pramfs: Persistent and protected ram filesystem
On Sat, 2009-06-13 at 15:20 +0200, Marco wrote: Are there any pending patents on this code? NO, there aren't patents pending on this code. MontaVista had a pending patent application but now it has abandoned this way. Daniel Walker can confirm that. Confirmed , there are no patents on this code. Daniel -- To unsubscribe from this list: send the line unsubscribe linux-embedded in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
