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

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Message-ID: <CAOJsxLHEHQOQsn9p8v6cq6SKM-E39WAy=CeaY=EN8gb9P5LEKQ@mail.gmail.com>
Date:	Mon, 26 Mar 2012 18:10:13 +0300
From:	Pekka Enberg <penberg@...nel.org>
To:	Mel Gorman <mel@....ul.ie>
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

Hi Mel,

On Mon, Mar 26, 2012 at 4:56 PM, Mel Gorman <mel@....ul.ie> wrote:
>> 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.

How about COMPACT_DISABLED?

The current API just doesn't make sense from practical point of view.
Anyone calling compaction_suitable() needs to do the COMPAT_BUILD
check first which is a non-obvious and error-prone API.

                        Pekka
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