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Re: mmap vs mtime in 2.6.26 and up

To: Ferenc Wagner <wferi@xxxxxxx>, Christoph Hellwig <hch@xxxxxxxxxxxxx>, Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>, xfs@xxxxxxxxxxx
Subject: Re: mmap vs mtime in 2.6.26 and up
From: Ray Lee <ray-lk@xxxxxxxxxxxxx>
Date: Tue, 12 May 2009 08:37:43 -0700
Cc: linux-kernel@xxxxxxxxxxxxxxx
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(Adding Christoph Hellwig, xfs list, Andrew Morton to cc:)

On Tue, May 12, 2009 at 5:32 AM, Ferenc Wagner <wferi@xxxxxxx> wrote:
> Hi,
>
> I've noticed that the last modification times of our RRD files got
> stuck after upgrading from 2.6.24 to 2.6.26 (Debian Etch -> Lenny; I
> also tested with 2.6.30-rc5, they are still stuck).  It has some
> literature, most notably kernel bug #2645, but that's closed long ago
> and the resulting patch http://lkml.org/lkml/2008/1/22/370 is present
> in my kernels.  Still, the test program (version 3 from the bug report)
> gives failures:
>
> $ ./mmap_test junk
> Modifying junk...
> Flushing data using sync()...
> Failure: time not changed.
> Not modifying junk...
> Flushing data using msync()...
> Success: time not changed.
> Not modifying junk...
> Flushing data using fsync()...
> Success: time not changed.
> Modifying junk...
> Flushing data using msync()...
> Failure: time not changed.
> Modifying junk...
> Flushing data using fsync()...
> Failure: time not changed.
>
> Is this as expected?  I reckon the bug wasn't solved fully, but it
> seems to be worse that that.


I don't think that's expected. Further, the test program (v3) from
that bugzilla http://bugzilla.kernel.org/show_bug.cgi?id=2645 works
for me under ext3, so perhaps this is an xfs-specific issue.


>
> I don't know if it's related or not, but another anomaly appeared
> after the upgrade: minutes-long remount times.  The machine always was
> under a fair load (10), but mount /usr -oremount,rw never took
> noticeable time.  The IO load pushes two other filesystems.  Now
> strace -tt shows:
>
> [...]
> 01:24:08.463813 stat64("/sbin/mount.xfs", 0xbfa40eb0) = -1 ENOENT (No such 
> file or directory)
> 01:24:08.463904 mount("/dev/mapper/noc7-usr", "/usr", 0x894a2c8, 
> MS_MGC_VAL|MS_NODEV|MS_REMOUNT, NULL) = 0
> 01:26:58.705387 readlink("/dev", 0xbfa3ef3b, 4096) = -1 EINVAL (Invalid 
> argument)
> [...]
>
> After this, remount ro and rw again are quick for some time.
> (I couldn't test this part with 2.6.30-rc5, but again, this may be
> totally unrelated.)
>
> This bug is quite serious in our environment, as it thwarts the backup
> software.  The file system is xfs; rw,nosuid,nodev,nobarrier,noquota.
> --
> Regards,
> Feri.

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