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SubjectRe: [PATCH 4/4] block: Optionally snapshot page contents to provide stable pages during write
On Fri, Dec 28, 2012 at 04:14:49AM +0900, OGAWA Hirofumi wrote:
> "Darrick J. Wong" <darrick.wong@oracle.com> writes:
>
> > diff --git a/include/uapi/linux/fs.h b/include/uapi/linux/fs.h
> > index 780d4c6..0144fbb 100644
> > --- a/include/uapi/linux/fs.h
> > +++ b/include/uapi/linux/fs.h
> > @@ -69,6 +69,7 @@ struct inodes_stat_t {
> > #define MS_REMOUNT 32 /* Alter flags of a mounted FS */
> > #define MS_MANDLOCK 64 /* Allow mandatory locks on an FS */
> > #define MS_DIRSYNC 128 /* Directory modifications are synchronous */
> > +#define MS_SNAP_STABLE 256 /* Snapshot pages during writeback, if needed */
> > #define MS_NOATIME 1024 /* Do not update access times. */
> > #define MS_NODIRATIME 2048 /* Do not update directory access times */
> > #define MS_BIND 4096
>
> I think this flag should be separated into "FS provide stable page" and
> "FS needs bounce buffer for stable page".
>
> My fs (I guess btrfs also) provides stable page by better way, and
> doesn't need to wait writeback flags too. What needs is just to avoid
> those stable page stuff.

How does your fs (are we talking about vfat?) provide stable pages?

btrfs creates its own bdi and doesn't set the "stable pages required" flag, so
it already skips all the stable page stuff.

--D
>
> Thanks.
> --
> OGAWA Hirofumi <hirofumi@mail.parknet.co.jp>
> --
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