Re: [RFC] VFS: File System Mount Wide O_DIRECT Support
> > The idea is simple, leave the desicion for the file system user to enable > > file system mount > > wide O_DIRECT support with a new mount option, for example, > I believe a better approach to your problem is actually to enable > loopback device driver to use direct IO. Someone was actually working on > this but I'm not sure where this ended up. Dave's been working on getting those patches merged. I'm also not sure where the work currently is, but here's an older posting: http://lwn.net/Articles/489647/ - z -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
Re: [RFC] VFS: File System Mount Wide O_DIRECT Support
On Tue, Sep 04, 2012 at 06:57:14AM -0400, Christoph Hellwig wrote: > On Tue, Sep 04, 2012 at 06:17:47PM +0800, Li Wang wrote: > > For file system created on file-backed loop device, there will be > > two-levels of > > page cache present, which typically doubles the memory consumption. > > And the right fix is to not use buffer I/O on the backing file instead > of hacks like this. That was my initial reaction too, but for the case of two VMs operating on the same device, it's better for it to be cached once in the hype-rvisor than twice in the VMs. Is that a common case worth optimising for? Probably not ... -- Matthew Wilcox Intel Open Source Technology Centre "Bill, look, we understand that you're interested in selling us this operating system, but compare it to ours. We can't possibly take such a retrograde step." -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
Re: [RFC] VFS: File System Mount Wide O_DIRECT Support
On Tue 04-09-12 18:17:47, Li Wang wrote: > For file system created on file-backed loop device, there will be two-levels > of > page cache present, which typically doubles the memory consumption. > In many cases, it is beneficial to turn on the O_DIRECT option while > performing > the upper file system file IO, to bypass the upper page cache, which not only > reduces half > of the memory consumption, but also improves the performance due to shorter > copy path. > > For example, the following iozone REREAD test with O_DIRECT turned on over > the one without > enjoys 10x speedup due to redundant cache elimination, consequently, avoiding > page cache thrashing > on a 2GB memory machine running 3.2.9 kernel. > > losetup /dev/loop0 dummy // dummy is a ext4 file with a size of 1.1GB > mkfs -t ext2 /dev/loop0 > mount /dev/loop0 /dsk > cd /dsk > iozone -t 1 -s 1G -r 4M -i 0 -+n -w // produce a 1GB test file > iozone -t 1 -s 1G -r 4M -i 1 -w // REREAD test without O_DIRECT > echo 1 > /proc/sys/vm/drop_caches // cleanup the page cache > iozone -t 1 -s 1G -r 4M -i 1 -w -I // REREAD test with O_DIRECT > > This feature is also expected to be useful for virtualization situation, the > file systems inside > the guest operation system will use much less of guest memory, which, > potencially results in less of > host memory use. Especially, it may be more useful if multiple guests are > running based > on a same disk image file. > > The idea is simple, leave the desicion for the file system user to enable > file system mount > wide O_DIRECT support with a new mount option, for example, I believe a better approach to your problem is actually to enable loopback device driver to use direct IO. Someone was actually working on this but I'm not sure where this ended up. Honza -- Jan Kara SUSE Labs, CR -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
Re: [RFC] VFS: File System Mount Wide O_DIRECT Support
On Tue, Sep 04, 2012 at 06:17:47PM +0800, Li Wang wrote: > For file system created on file-backed loop device, there will be two-levels > of > page cache present, which typically doubles the memory consumption. And the right fix is to not use buffer I/O on the backing file instead of hacks like this. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
Re: [RFC] VFS: File System Mount Wide O_DIRECT Support
On Tue, Sep 04, 2012 at 06:17:47PM +0800, Li Wang wrote: For file system created on file-backed loop device, there will be two-levels of page cache present, which typically doubles the memory consumption. And the right fix is to not use buffer I/O on the backing file instead of hacks like this. -- To unsubscribe from this list: send the line unsubscribe linux-kernel in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
Re: [RFC] VFS: File System Mount Wide O_DIRECT Support
On Tue 04-09-12 18:17:47, Li Wang wrote: For file system created on file-backed loop device, there will be two-levels of page cache present, which typically doubles the memory consumption. In many cases, it is beneficial to turn on the O_DIRECT option while performing the upper file system file IO, to bypass the upper page cache, which not only reduces half of the memory consumption, but also improves the performance due to shorter copy path. For example, the following iozone REREAD test with O_DIRECT turned on over the one without enjoys 10x speedup due to redundant cache elimination, consequently, avoiding page cache thrashing on a 2GB memory machine running 3.2.9 kernel. losetup /dev/loop0 dummy // dummy is a ext4 file with a size of 1.1GB mkfs -t ext2 /dev/loop0 mount /dev/loop0 /dsk cd /dsk iozone -t 1 -s 1G -r 4M -i 0 -+n -w // produce a 1GB test file iozone -t 1 -s 1G -r 4M -i 1 -w // REREAD test without O_DIRECT echo 1 /proc/sys/vm/drop_caches // cleanup the page cache iozone -t 1 -s 1G -r 4M -i 1 -w -I // REREAD test with O_DIRECT This feature is also expected to be useful for virtualization situation, the file systems inside the guest operation system will use much less of guest memory, which, potencially results in less of host memory use. Especially, it may be more useful if multiple guests are running based on a same disk image file. The idea is simple, leave the desicion for the file system user to enable file system mount wide O_DIRECT support with a new mount option, for example, I believe a better approach to your problem is actually to enable loopback device driver to use direct IO. Someone was actually working on this but I'm not sure where this ended up. Honza -- Jan Kara j...@suse.cz SUSE Labs, CR -- To unsubscribe from this list: send the line unsubscribe linux-kernel in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
Re: [RFC] VFS: File System Mount Wide O_DIRECT Support
On Tue, Sep 04, 2012 at 06:57:14AM -0400, Christoph Hellwig wrote: On Tue, Sep 04, 2012 at 06:17:47PM +0800, Li Wang wrote: For file system created on file-backed loop device, there will be two-levels of page cache present, which typically doubles the memory consumption. And the right fix is to not use buffer I/O on the backing file instead of hacks like this. That was my initial reaction too, but for the case of two VMs operating on the same device, it's better for it to be cached once in the hype-rvisor than twice in the VMs. Is that a common case worth optimising for? Probably not ... -- Matthew Wilcox Intel Open Source Technology Centre Bill, look, we understand that you're interested in selling us this operating system, but compare it to ours. We can't possibly take such a retrograde step. -- To unsubscribe from this list: send the line unsubscribe linux-kernel in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
Re: [RFC] VFS: File System Mount Wide O_DIRECT Support
The idea is simple, leave the desicion for the file system user to enable file system mount wide O_DIRECT support with a new mount option, for example, I believe a better approach to your problem is actually to enable loopback device driver to use direct IO. Someone was actually working on this but I'm not sure where this ended up. Dave's been working on getting those patches merged. I'm also not sure where the work currently is, but here's an older posting: http://lwn.net/Articles/489647/ - z -- To unsubscribe from this list: send the line unsubscribe linux-kernel in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
