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

["Bryn M. Reeves" <breeves@redhat.com>]

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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.
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