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    SubjectRe: vfs: Add MS_FLUSHONFSYNC mount flag
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    On Thu, 2009-02-12 at 11:13 -0600, Eric Sandeen wrote:
    > Fernando Luis Vázquez Cao wrote:
    > > This mount flag will be used to determine whether the block device's write
    > > cache should be flush or not on fsync()/fdatasync().
    > >
    > > Signed-off-by: Fernando Luis Vazquez Cao <fernando@oss.ntt.co.jp>
    > > ---
    >
    > Again, apologies for chiming in late.
    >
    > But wouldn't it be better to make this a block device property rather
    > than a new filesystem mount option?
    >
    > That way the filesystem can always do "the right thing" and call the
    > blkdev flush on fsync.
    >
    > The block device *could* choose to ignore this in hardware if it knows
    > it's built with a nonvolatile write cache or if it has no write cache.
    >
    > Somewhere in the middle, if an administrator knows they have a UPS they
    > trust and hardware that stays connected to it, they could tune the bdev
    > to ignore these flush requests.
    >
    > Also that way if you have 8 partitions on a battery-backed blockdev, you
    > can tune it once, instead of needing to mount all 8 filesystems with the
    > new option.

    The main reason I decided to go for the mount option approach is to be
    consistent with what we do when it comes to write barriers. Treating one
    as a mount option and the other as a (possibly) sysfs tunable property
    seems a bit confusing to me.

    Do you suggest using sysfs tunables instead?

    - Fernando

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