[PATCH 02/17] xfs: skip writeback from reclaim context

[Dave Chinner]

On Mon, May 31, 2010 at 12:07:29PM -0400, Christoph Hellwig wrote:
> Allowing writeback from reclaim context causes massive problems with stack
> overflows as we can call into the writeback code which tends to be a heavy
> stack user both in the generic code and XFS from random contexts that
> perform memory allocations.
> 
> Follow the example of btrfs (and in slightly different form ext4) and refuse
> to write out data from reclaim context.  This issue should really be handled
> by the VM so that we can tune better for this case, but until we get it
> sorted out there we have to hack around this in each filesystem with a
> complex writeback path.
> 
> Signed-off-by: Christoph Hellwig <hch at lst.de>

Yup, I agree that we have to do this for the moment. It hasn't
caused any problems in my usual OOM testing, so it seems safe
to do.

Reviewed-by: Dave Chinner <dchinner at redhat.com>

Also worth thinking about is if should be checked in
xfs_vm_releasepage() as well to avoid the same stack issues if it
triggers allocation...

Cheers,

Dave.
-- 
Dave Chinner
david at fromorbit.com