Re: btrfs and swap files on SSD's ?
Hey Cris, Chris Mason wrote: This doesn't quite play nicely with btrfs and should lead to all kinds of problemsI'm looking into how to disable swapfiles completely. Please try to support swapfiles. I know their drawbacks and still use them quite often. Cheers Kaspar -- To unsubscribe from this list: send the line unsubscribe linux-btrfs in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: btrfs and swap files on SSD's ?
On Wed, Jan 21, 2009 at 12:02 AM, Chris Mason chris.ma...@oracle.com wrote: There are patches to support swap over NFS that might make it safe to use on btrfs. At any rate, it is a fixable problem. FreeBSD has been able to run swap over NFS for as long as I can remember, what is different in Linux that makes it especially difficult? I've read that swap over non-trivial filesystems is hazardous as it may lead to a situation in which memory allocation can fail in the swap/FS code that was meant to make allocation possible again. If btrfs is to take the role of a RAID and volume manager, it would certainly be very useful to be able to run swap on it, since that frees up other volumes from an administrative standpoint. -- Dmitri Nikulin Centre for Synchrotron Science Monash University Victoria 3800, Australia -- To unsubscribe from this list: send the line unsubscribe linux-btrfs in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: btrfs and swap files on SSD's ?
The second is an implementation detail of the linux swap file code. It expects filesystems don't move blocks around, and takes a mapping of the blocks in the FS once. This doesn't work with btrfs because we do move blocks around all the time. That's interesting. I have a few questions: -Is creating a loopback device from the file any different, or does that lead to the same problems? -Would mounting a filesystem image via loopback device cause similar problems? -Would this be viable if using a dedicated nodatacow subvolume, or is that still too risky because of the odd case where you do cow? -Does online defragmentation hurt this as well? Cheers, -Anthony -- To unsubscribe from this list: send the line unsubscribe linux-btrfs in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: btrfs and swap files on SSD's ?
Dmitri Nikulin dniku...@gmail.com writes: On Wed, Jan 21, 2009 at 12:02 AM, Chris Mason chris.ma...@oracle.com wrote: There are patches to support swap over NFS that might make it safe to use on btrfs. At any rate, it is a fixable problem. FreeBSD has been able to run swap over NFS for as long as I can remember, what is different in Linux that makes it especially difficult? One big traditional difference is that FreeBSD uses fixed isolated pools for their networking buffers (that is why you had to tune most systems for higher network workloads), while Linux has fully unified[1] memory management including the network stack. Now I believe recent BSD also moved to more unified network management and it wouldn't surprise me if they had trouble with this now too. [1] at least for now, there are unfortunately some tendencies to move back to fixed pools too. I've read that swap over non-trivial filesystems is hazardous as it may lead to a situation in which memory allocation can fail in the swap/FS code that was meant to make allocation possible again. A lot of this has been fixed in the 2.6 timeframe (e.g. there's now a better enforced global dirty limit), but there are likely still corner cases that could run into difficulties, so noone is really declaring it 100% safe yet. If btrfs is to take the role of a RAID and volume manager, it would certainly be very useful to be able to run swap on it, since that frees up other volumes from an administrative standpoint. The fixed extent mapping of the swap files is really a different problem, independent of the memory allocation issue. In general the memory allocation problem on write out has to be solved in any ways (even if you don't support swap files), because any dirty mmap'ed file effectively acts like a swap file. -Andi -- a...@linux.intel.com -- Speaking for myself only. -- To unsubscribe from this list: send the line unsubscribe linux-btrfs in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
