Messages in this thread | | | Date | Thu, 15 Jan 2009 09:16:55 +1100 | From | Dave Chinner <> | Subject | Re: spurious -ENOSPC on XFS |
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On Tue, Jan 13, 2009 at 04:58:01PM +1100, Lachlan McIlroy wrote: > Christoph Hellwig wrote: >> On Mon, Jan 12, 2009 at 06:14:36AM -0500, Mikulas Patocka wrote: >>> Hi >>> >>> I discovered a bug in XFS in delayed allocation. >>> >>> When you take a small partition (52MB in my case) and copy many small >>> files on it (source code) that barely fits there, you get -ENOSPC. >>> Then sync the partition, some free space pops up, click "retry" in MC >>> an the copy continues. They you get again -ENOSPC, you must sync, >>> click "retry" and go on. And so on few times until the source code >>> finally fits on the XFS partition. >>> >>> This misbehavior is apparently caused by delayed allocation, delayed >>> allocation does not exactly know how much space will be occupied by >>> data, so it makes some upper bound guess. Because free space count is >>> only a guess, not the actual data being consumed, XFS should not >>> return -ENOSPC on behalf of it. When the free space overflows, XFS >>> should sync itself, retry allocation and only return -ENOSPC if it >>> fails the second time, after the sync. > This sounds like a problem with speculative allocation - delayed allocations > beyond eof. Even if we write a small file, say 4k, a 64k chunk of delayed > allocation will be credited to the file.
The second retry occurs without speculative EOF allocation. That's what the BMAPI_SYNC flag does....
That being said, it can't truncate away pre-existing speculative allocations on other files, which is why there is a global flush and wait before the third retry.....
Cheers,
Dave. -- Dave Chinner david@fromorbit.com
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