Re: [PATCH] Freeze bdevs when freezing processes.
- From: "Rafael J. Wysocki" <rjw@xxxxxxx>
- Date: Wed, 25 Oct 2006 21:05:56 +0200
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
--
You never change things by fighting the existing reality.
R. Buckminster Fuller
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