linux-kernel - Re: [PATCH 4/8] btrfs: Warn if direct reclaim tries to writeback pages

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Date:	Wed, 3 Aug 2011 13:10:31 +0200
From:	Johannes Weiner <jweiner@...hat.com>
To:	Mel Gorman <mgorman@...e.de>
Cc:	Linux-MM <linux-mm@...ck.org>, LKML <linux-kernel@...r.kernel.org>,
	XFS <xfs@....sgi.com>, Dave Chinner <david@...morbit.com>,
	Christoph Hellwig <hch@...radead.org>,
	Wu Fengguang <fengguang.wu@...el.com>, Jan Kara <jack@...e.cz>,
	Rik van Riel <riel@...hat.com>,
	Minchan Kim <minchan.kim@...il.com>
Subject: Re: [PATCH 4/8] btrfs: Warn if direct reclaim tries to writeback
 pages

On Thu, Jul 21, 2011 at 05:28:46PM +0100, Mel Gorman wrote:
> Direct reclaim should never writeback pages. Warn if an attempt is
> made. By rights, btrfs should be allowing writepage from kswapd if
> it is failing to reclaim pages by any other means but it's outside
> the scope of this patch.
> 
> Signed-off-by: Mel Gorman <mgorman@...e.de>
> ---
>  fs/btrfs/disk-io.c |    2 ++
>  fs/btrfs/inode.c   |    2 ++
>  2 files changed, 4 insertions(+), 0 deletions(-)
> 
> diff --git a/fs/btrfs/disk-io.c b/fs/btrfs/disk-io.c
> index 1ac8db5d..cc9c9cf 100644
> --- a/fs/btrfs/disk-io.c
> +++ b/fs/btrfs/disk-io.c
> @@ -829,6 +829,8 @@ static int btree_writepage(struct page *page, struct writeback_control *wbc)
>  
>  	tree = &BTRFS_I(page->mapping->host)->io_tree;
>  	if (!(current->flags & PF_MEMALLOC)) {
> +		WARN_ON_ONCE((current->flags & (PF_MEMALLOC|PF_KSWAPD)) ==
> +								PF_MEMALLOC);

Since it is branch for PF_MEMALLOC being set, why not just
WARN_ON_ONCE(!(current->flags & PF_KSWAPD)) instead?

Minor nitpick, though, and I can understand if you just want to have
the conditionals be the same in every fs.

Acked-by: Johannes Weiner <jweiner@...hat.com>
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