[linux-lvm] Page cache corruption when creating a snapshot

[Bryn M. Reeves]

-----BEGIN PGP SIGNED MESSAGE-----
Hash: SHA1

Greg Hudson wrote:
> Nope, that never made it go away.  I'm not sure in what situations
> flushing write buffers would have any effect.  If I had a way to throw
> away the read-only page cache and force a file reload from disk, I would
> expect that to eliminate the visible effect of the corruption; at the
> moment the only reliable way I know how to do that is to reboot.  (I
> could churn the page cache into oblivion with a bazillion reads of
> different files, but I'd have no way of knowing when I had succeeded in
> reusing the corrupted cache page.)

You should be able to achieve that via the /proc/sys/vm/drop_caches sysctl:

Documentation/filesystems/proc.txt:

drop_caches
- -----------

Writing to this will cause the kernel to drop clean caches, dentries and
inodes from memory, causing that memory to become free.

To free pagecache:
        echo 1 > /proc/sys/vm/drop_caches
To free dentries and inodes:
        echo 2 > /proc/sys/vm/drop_caches
To free pagecache, dentries and inodes:
        echo 3 > /proc/sys/vm/drop_caches


I guess a 1 would be a good first try & if that doesn't clear it, a 3
should force the entire inode to be re-read from disk.

Regards,
Bryn.
-----BEGIN PGP SIGNATURE-----
Version: GnuPG v1.4.7 (GNU/Linux)
Comment: Using GnuPG with Fedora - http://enigmail.mozdev.org

iD8DBQFHyFia6YSQoMYUY94RArInAJ9dRVLCGYXcllL4RDz4pei4qGnUVQCg4LL1
d22/7jgF5zxsGnFPeCfpkwA=
=v99d
-----END PGP SIGNATURE-----