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

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Message-ID: <20110803134507.GI19099@suse.de>
Date:	Wed, 3 Aug 2011 14:45:07 +0100
From:	Mel Gorman <mgorman@...e.de>
To:	Johannes Weiner <jweiner@...hat.com>
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 Wed, Aug 03, 2011 at 01:10:31PM +0200, Johannes Weiner wrote:
> 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.
> 

It was just copying the conditionals for the other FS although I admit
your version would look nicer.

-- 
Mel Gorman
SUSE Labs
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