Re: [PATCH 2/8] xfs: Warn if direct reclaim tries to writeback pages

[Christoph Hellwig <hch@xxxxxxxxxxxxx>]

On Thu, Jul 21, 2011 at 05:28:44PM +0100, Mel Gorman wrote:
> --- a/fs/xfs/linux-2.6/xfs_aops.c
> +++ b/fs/xfs/linux-2.6/xfs_aops.c
> @@ -930,12 +930,13 @@ xfs_vm_writepage(
>        * random callers for direct reclaim or memcg reclaim.  We explicitly
>        * allow reclaim from kswapd as the stack usage there is relatively low.
>        *
> -      * This should really be done by the core VM, but until that happens
> -      * filesystems like XFS, btrfs and ext4 have to take care of this
> -      * by themselves.
> +      * This should never happen except in the case of a VM regression so
> +      * warn about it.
>        */
> -     if ((current->flags & (PF_MEMALLOC|PF_KSWAPD)) == PF_MEMALLOC)
> +     if ((current->flags & (PF_MEMALLOC|PF_KSWAPD)) == PF_MEMALLOC) {
> +             WARN_ON_ONCE(1);
>               goto redirty;

The nicer way to write this is

        if (WARN_ON(current->flags & (PF_MEMALLOC|PF_KSWAPD)) == PF_MEMALLOC)
                goto redirty;