>>> On 7/2/2014 at 11:10 AM, in message <53b37840.1020...@redhat.com>, Eric >>> Blake <ebl...@redhat.com> wrote: > On 07/01/2014 02:48 AM, Stefan Hajnoczi wrote: > > From: Chunyan Liu <cy...@suse.com> > > > > Add 'nocow' option so that users could have a chance to set NOCOW flag to > > newly created files. It's useful on btrfs file system to enhance > performance. > > > > Btrfs has low performance when hosting VM images, even more when the guest > > in those VM are also using btrfs as file system. One way to mitigate this > bad > > performance is to turn off COW attributes on VM files. Generally, there are > > two ways to turn off NOCOW on btrfs: a) by mounting fs with nodatacow, then > > all newly created files will be NOCOW. b) per file. Add the NOCOW file > > attribute. It could only be done to empty or new files. > > > > This patch tries the second way, according to the option, it could add > NOCOW > > per file. > > > > For most block drivers, since the create file step is in raw-posix.c, so we > > can do setting NOCOW flag ioctl in raw-posix.c only. > > > > But there are some exceptions, like block/vpc.c and block/vdi.c, they are > > creating file by calling qemu_open directly. For them, do the same setting > > NOCOW flag ioctl work in them separately. > > > > [Fixed up 082.out due to the new 'nocow' creation option > > --Stefan] > > > > Signed-off-by: Chunyan Liu <cy...@suse.com> > > Signed-off-by: Stefan Hajnoczi <stefa...@redhat.com> > > I see this is already in qemu.git, so it will need a followup to fix the > user-visible typos (s/trun/turn/, s/Capitabl/Capital/) >
http://thread.gmane.org/gmane.comp.emulators.qemu/284536 -Chunyan > -- > Eric Blake eblake redhat com +1-919-301-3266 > Libvirt virtualization library http://libvirt.org > >
