linux-kernel - Re: [PATCH] Re: kswapd stuck using 100% CPU

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Message-ID: <20120326135609.GM1007@csn.ul.ie>
Date:	Mon, 26 Mar 2012 14:56:09 +0100
From:	Mel Gorman <mel@....ul.ie>
To:	Pekka Enberg <penberg@...nel.org>
Cc:	Rik van Riel <riel@...hat.com>, Anton Blanchard <anton@...ba.org>,
	aarcange@...hat.com, akpm@...ux-foundation.org, hughd@...gle.com,
	lkml <linux-kernel@...r.kernel.org>, linux-mm@...ck.org,
	Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [PATCH] Re: kswapd stuck using 100% CPU

On Mon, Mar 26, 2012 at 01:40:41PM +0300, Pekka Enberg wrote:
> On Mon, Mar 26, 2012 at 12:32 PM, Mel Gorman <mel@....ul.ie> wrote:
> > On Sat, Mar 24, 2012 at 10:26:21AM -0400, Rik van Riel wrote:
> >>
> >> Only test compaction_suitable if the kernel is built with CONFIG_COMPACTION,
> >> otherwise the stub compaction_suitable function will always return
> >> COMPACT_SKIPPED and send kswapd into an infinite loop.
> >>
> >> Signed-off-by: Rik van Riel <riel@...hat.com>
> >> Reported-by: Anton Blanchard <anton@...ba.org>
> >
> > Acked-by: Mel Gorman <mel@....ul.ie>
> 
> The API looks fragile and this patch isn't exactly making it any
> better. Why don't we make compaction_suitable() return something other
> than COMPACT_SKIPPED for !CONFIG_COMPACTION case?
> 

Returning COMPACT_PARTIAL or COMPACT_CONTINUE would confuse the check in
should_continue_reclaim. A fourth return type could be added but an
obvious name does not spring to mind that would end up being similar to
just adding a CONFIG_COMPACTION check.

-- 
Mel Gorman
SUSE Labs
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