Re: [PHP-DEV] Re: Zend mm
You should take care not to mistake the GC and the MM, they are two different things and surprisingly, they dont interact with each other. Zend GC is a layer above Zend MM, and Zend GC can be totally disabled, Zend MM cant at all. Zend MM is a BIG layer over malloc()/free() which goals are mainly to abstract the OS MM (mainly Unix/Win32) and to avoid memory fragmentation and too many system calls which could lead to performance problems. Lots of other programms use such a tool, like Apache httpd for example. Zend MM can also help you (in debug mode only) by showing its state after a script has run, alowing you to easily track memory leaks while using it (e**() functions) without the need to use tools such as valgrind. ZendMM can track all the PHP memory usage, and provide feature such as "memory_limit". Finally, ZendMM is a super malloc(), it nearly can be foreseen as a custom implementation of libc malloc() using a heap over the heap and trying to optimize it as possible. Simply looking at the structs in zend_alloc.h let you guess it's goal, but you need to know how memory management works in computer programs for that. Julien.P On Wed, Feb 2, 2011 at 7:52 AM, Adi Mutu wrote: > > Thanks a lot, for all the help about zend mm guys, i'm very grateful. > Thanks,A. > > --- On Sun, 1/30/11, Ben Schmidt wrote: > > From: Ben Schmidt > Subject: Re: [PHP-DEV] Re: Zend mm > To: "Adi Mutu" > Cc: internals@lists.php.net, t...@daylessday.org > Date: Sunday, January 30, 2011, 4:45 PM > > On 30/01/11 4:11 AM, Adi Mutu wrote: >> I have looked at the sources, but i'm only at the begining of >> analyzing the php sources.i've understand how to write extensions >> for example, but this memory manager seems more complicated to me. > > Yes, it is. Memory management is a low-level and subtle area. It takes a > lot of careful thought to design and even to understand the algorithms > involved. It is hard to debug, because an error caused in one place may > not show itself until completely different code is executing. It is also > an area which doesn't change much. Almost all the other code in the PHP > interpreter, and therefore PHP scripts themselves, rely on the memory > manager code doing its job unintrusively and correctly, so once it is > working well, it tends to be left that way, except for fixing small bugs > as they are found, or a big and careful development effort to address > some limitation (e.g. improving the garbage collection to collect > cycles, which was something done fairly recently). > > The bottom line is that this is not an area that is all that easy for > beginners to get their teeth into. But it's also an area that isn't > necessary for beginners to understand in much detail, either. Unless you > have a particular project in mind that involves the memory manager, you > probably don't need to touch it. > > I don't want to discourage you, but just point out that perhaps this is > something you might look at later, or even not at all, as you may find > there are many worthwhile projects that take up all your time before you > ever get to understanding the memory manager fully. > >> It would be useful if for example, could explain me the structures >> that are used in the Zend memory manager, how they're chained >> etc.and if you can tell me in words what do zend_mm_aloc_int() and >> zend_mm_free_int() basically do...Thank you for your time,Adrian > > I suspect these structures and functions are fairly easy to understand > by someone familiar with the area of memory management, which is why you > have been advised to consult the source code. So perhaps what you need > to do is not learn about PHP's memory manager, but just learn about > memory management in general. Then it should be fairly easy to > understand what PHP's memory manager is doing from its code. > > I'm afraid I doubt the people here have the time to teach you this over > email. :-) So here are some references which might be of use to you. > > - I believe the 'standard textbook' for learning about memory management > is this one here: > http://www.cs.kent.ac.uk/people/staff/rej/gcbook/gcbook.html > > - This page also mentions that a new edition is due out soon: > http://c2.com/cgi/wiki?GarbageCollectionBook > > - You can also check out this site: http://www.memorymanagement.org/ > > - Relating this to, PHP: PHP is a garbage collected language which I > believe uses reference counting and a clever collector to detect and > free cycles. I haven't looked in detail into the implementation, but I > know some documentation is available on the subject here: > http://www.php.net/manual/en/features.gc.php > > Hope this helps! > > Ben. > > > > > > > -- PHP Internals - PHP Runtime Development Mailing List To unsubscribe, visit: http://www.php.net/unsub.php
Re: [PHP-DEV] Re: Zend mm
Thanks a lot, for all the help about zend mm guys, i'm very grateful. Thanks,A. --- On Sun, 1/30/11, Ben Schmidt wrote: From: Ben Schmidt Subject: Re: [PHP-DEV] Re: Zend mm To: "Adi Mutu" Cc: internals@lists.php.net, t...@daylessday.org Date: Sunday, January 30, 2011, 4:45 PM On 30/01/11 4:11 AM, Adi Mutu wrote: > I have looked at the sources, but i'm only at the begining of > analyzing the php sources.i've understand how to write extensions > for example, but this memory manager seems more complicated to me. Yes, it is. Memory management is a low-level and subtle area. It takes a lot of careful thought to design and even to understand the algorithms involved. It is hard to debug, because an error caused in one place may not show itself until completely different code is executing. It is also an area which doesn't change much. Almost all the other code in the PHP interpreter, and therefore PHP scripts themselves, rely on the memory manager code doing its job unintrusively and correctly, so once it is working well, it tends to be left that way, except for fixing small bugs as they are found, or a big and careful development effort to address some limitation (e.g. improving the garbage collection to collect cycles, which was something done fairly recently). The bottom line is that this is not an area that is all that easy for beginners to get their teeth into. But it's also an area that isn't necessary for beginners to understand in much detail, either. Unless you have a particular project in mind that involves the memory manager, you probably don't need to touch it. I don't want to discourage you, but just point out that perhaps this is something you might look at later, or even not at all, as you may find there are many worthwhile projects that take up all your time before you ever get to understanding the memory manager fully. > It would be useful if for example, could explain me the structures > that are used in the Zend memory manager, how they're chained > etc.and if you can tell me in words what do zend_mm_aloc_int() and > zend_mm_free_int() basically do...Thank you for your time,Adrian I suspect these structures and functions are fairly easy to understand by someone familiar with the area of memory management, which is why you have been advised to consult the source code. So perhaps what you need to do is not learn about PHP's memory manager, but just learn about memory management in general. Then it should be fairly easy to understand what PHP's memory manager is doing from its code. I'm afraid I doubt the people here have the time to teach you this over email. :-) So here are some references which might be of use to you. - I believe the 'standard textbook' for learning about memory management is this one here: http://www.cs.kent.ac.uk/people/staff/rej/gcbook/gcbook.html - This page also mentions that a new edition is due out soon: http://c2.com/cgi/wiki?GarbageCollectionBook - You can also check out this site: http://www.memorymanagement.org/ - Relating this to, PHP: PHP is a garbage collected language which I believe uses reference counting and a clever collector to detect and free cycles. I haven't looked in detail into the implementation, but I know some documentation is available on the subject here: http://www.php.net/manual/en/features.gc.php Hope this helps! Ben.
Re: [PHP-DEV] Re: Zend mm
Am 31.01.2011 01:45, schrieb Ben Schmidt: > - Relating this to, PHP: PHP is a garbage collected language which I > believe uses reference counting and a clever collector to detect and > free cycles. I haven't looked in detail into the implementation, but I > know some documentation is available on the subject here: > http://www.php.net/manual/en/features.gc.php http://www.research.ibm.com/people/d/dfb/papers/Bacon01Concurrent.pdf is the algorithm used by PHP's garbage collector. -- Sebastian BergmannCo-Founder and Principal Consultant http://sebastian-bergmann.de/ http://thePHP.cc/ -- PHP Internals - PHP Runtime Development Mailing List To unsubscribe, visit: http://www.php.net/unsub.php
Re: [PHP-DEV] Re: Zend mm
On 30/01/11 4:11 AM, Adi Mutu wrote: > I have looked at the sources, but i'm only at the begining of > analyzing the php sources.i've understand how to write extensions > for example, but this memory manager seems more complicated to me. Yes, it is. Memory management is a low-level and subtle area. It takes a lot of careful thought to design and even to understand the algorithms involved. It is hard to debug, because an error caused in one place may not show itself until completely different code is executing. It is also an area which doesn't change much. Almost all the other code in the PHP interpreter, and therefore PHP scripts themselves, rely on the memory manager code doing its job unintrusively and correctly, so once it is working well, it tends to be left that way, except for fixing small bugs as they are found, or a big and careful development effort to address some limitation (e.g. improving the garbage collection to collect cycles, which was something done fairly recently). The bottom line is that this is not an area that is all that easy for beginners to get their teeth into. But it's also an area that isn't necessary for beginners to understand in much detail, either. Unless you have a particular project in mind that involves the memory manager, you probably don't need to touch it. I don't want to discourage you, but just point out that perhaps this is something you might look at later, or even not at all, as you may find there are many worthwhile projects that take up all your time before you ever get to understanding the memory manager fully. > It would be useful if for example, could explain me the structures > that are used in the Zend memory manager, how they're chained > etc.and if you can tell me in words what do zend_mm_aloc_int() and > zend_mm_free_int() basically do...Thank you for your time,Adrian I suspect these structures and functions are fairly easy to understand by someone familiar with the area of memory management, which is why you have been advised to consult the source code. So perhaps what you need to do is not learn about PHP's memory manager, but just learn about memory management in general. Then it should be fairly easy to understand what PHP's memory manager is doing from its code. I'm afraid I doubt the people here have the time to teach you this over email. :-) So here are some references which might be of use to you. - I believe the 'standard textbook' for learning about memory management is this one here: http://www.cs.kent.ac.uk/people/staff/rej/gcbook/gcbook.html - This page also mentions that a new edition is due out soon: http://c2.com/cgi/wiki?GarbageCollectionBook - You can also check out this site: http://www.memorymanagement.org/ - Relating this to, PHP: PHP is a garbage collected language which I believe uses reference counting and a clever collector to detect and free cycles. I haven't looked in detail into the implementation, but I know some documentation is available on the subject here: http://www.php.net/manual/en/features.gc.php Hope this helps! Ben. -- PHP Internals - PHP Runtime Development Mailing List To unsubscribe, visit: http://www.php.net/unsub.php
[PHP-DEV] Re: Zend mm
I have looked at the sources, but i'm only at the begining of analyzing the php sources.i've understand how to write extensions for example, but this memory manager seems more complicated to me. It would be useful if for example, could explain me the structures that are used in the Zend memory manager, how they're chained etc.and if you can tell me in words what do zend_mm_aloc_int() and zend_mm_free_int() basically do...Thank you for your time,Adrian
