[PATCH] xfs: allow writeback from kswapd

[Alex Elder]

On Mon, 2010-06-28 at 10:34 -0400, Christoph Hellwig wrote:
> We only need disable I/O from direct or memcg reclaim.
> 
> Signed-off-by: Christoph Hellwig <hch at lst.de>

Looks good.

Reviewed-by: Alex Elder <aelder at sgi.com>


> Index: xfs-dev/fs/xfs/linux-2.6/xfs_aops.c
> ===================================================================
> --- xfs-dev.orig/fs/xfs/linux-2.6/xfs_aops.c	2010-06-28 11:57:06.652261386 +0200
> +++ xfs-dev/fs/xfs/linux-2.6/xfs_aops.c	2010-06-28 11:59:17.846068204 +0200
> @@ -1049,16 +1049,15 @@ xfs_vm_writepage(
>  	/*
>  	 * Refuse to write the page out if we are called from reclaim context.
>  	 *
> -	 * This is primarily to avoid stack overflows when called from deep
> -	 * used stacks in random callers for direct reclaim, but disabling
> -	 * reclaim for kswap is a nice side-effect as kswapd causes rather
> -	 * suboptimal I/O patters, too.
> +	 * This avoids stack overflows when called from deeply used stacks in
> +	 * 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.
>  	 */
> -	if (current->flags & PF_MEMALLOC)
> +	if ((current->flags & (PF_MEMALLOC|PF_KSWAPD)) == PF_MEMALLOC)
>  		goto out_fail;
>  
>  	/*
> 
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