Messages in this thread | | | From | "Rafael J. Wysocki" <> | Subject | Re: [PATCH] Freeze bdevs when freezing processes. | Date | Wed, 25 Oct 2006 10:12:58 +0200 |
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On Wednesday, 25 October 2006 02:13, David Chinner wrote: > On Tue, Oct 24, 2006 at 11:37:37PM +0200, Pavel Machek wrote: > > Hi! > > > > > > Do you mean calling sys_sync() after the userspace has been frozen > > > > may not be sufficient? > > > > > > In most cases it probably is, but sys_sync() doesn't provide any > > > guarantees that the filesystem is not being used or written to after > > > it completes. Given that every so often I hear about an XFS filesystem > > > that was corrupted by suspend, I don't think this is sufficient... > > > > Userspace is frozen. There's noone that can write to the XFS > > filesystem. > > Sure, no new userspace processes can write data, but what about the > internal state of the filesystem? > > All a sync guarantees is that the filesystem is consistent when the > sync returns and XFS provides this guarantee by writing all data and > ensuring all metadata changes are logged so if a crash occurs it can > be recovered (which provides the sync guarantee). hence after a > sys_sync(), XFS will still have lots of dirty metadata that needs to > be written to disk at some time in the future so the transactions > can be removed from the log. > > This dirty metadata can be flushed at any time, and the dirty state > is kept in XFS structures and not always in page structures (think > multipage metadata buffers).
Are the dirty metadata flushed by a kernel thread?
Greetings, Rafael
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