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    SubjectRe: [PATCH] Freeze bdevs when freezing processes.
    Date
    On Wednesday, 25 October 2006 15:23, Nigel Cunningham wrote:
    > Hi.
    >
    > On Wed, 2006-10-25 at 14:32 +0200, Rafael J. Wysocki wrote:
    > > On Wednesday, 25 October 2006 10:47, Pavel Machek wrote:
    > > > On Wed 2006-10-25 18:38:30, David Chinner wrote:
    > > > > On Wed, Oct 25, 2006 at 10:10:01AM +0200, Pavel Machek wrote:
    > > > > > > Hence the only way to correctly rebuild the XFS state on resume is
    > > > > > > to quiesce the filesystem on suspend and thaw it on resume so as to
    > > > > > > trigger log recovery.
    > > > > >
    > > > > > No, during suspend/resume, memory image is saved, and no state is
    > > > > > lost. We would not even have to do sys_sync(), and suspend/resume
    > > > > > would still work properly.
    > > > >
    > > > > It seems to me that you ensure the filesystem is synced to disk and
    > > > > then at some point later you record the memory state of the
    > > > > filesystem, but these happen at different times. That leaves a
    > > > > window for things to get out of sync again, right?
    > > >
    > > > I DO NOT HAVE TO ENSURE FILESYSTEM IS SYNCED. That sys_sync() is
    > > > optional.
    > > >
    > > > Recording of memory state is atomic, and as long as noone writes to
    > > > the disk after atomic snapshot, memory image matches what is on disk.
    > >
    > > Well, my impression is that this is exactly what happens here: Something
    > > in the XFS code causes metadata to be written to disk _after_ the atomic
    > > snapshot.
    > >
    > > That's why I asked if the dirty XFS metadata were flushed by a kernel thread.
    >
    > When I first added bdev freezing it was because there was an XFS timer
    > doing writes.

    Yes, I noticed you said that, but I'd like someone from the XFS team to either
    confirm or deny it.

    Greetings,
    Rafael


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