linux-kernel - Re: [PATCH 1/2] mm: vmscan: Remove lumpy reclaim

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Message-ID: <20120410082454.GA3789@suse.de>
Date:	Tue, 10 Apr 2012 09:24:54 +0100
From:	Mel Gorman <mgorman@...e.de>
To:	Ying Han <yinghan@...gle.com>
Cc:	Linux-MM <linux-mm@...ck.org>, LKML <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Rik van Riel <riel@...hat.com>,
	Konstantin Khlebnikov <khlebnikov@...nvz.org>,
	Hugh Dickins <hughd@...gle.com>
Subject: Re: [PATCH 1/2] mm: vmscan: Remove lumpy reclaim

On Fri, Apr 06, 2012 at 04:52:09PM -0700, Ying Han wrote:
> On Wed, Mar 28, 2012 at 9:06 AM, Mel Gorman <mgorman@...e.de> wrote:
> > Lumpy reclaim had a purpose but in the mind of some, it was to kick
> > the system so hard it trashed. For others the purpose was to complicate
> > vmscan.c. Over time it was giving softer shoes and a nicer attitude but
> > memory compaction needs to step up and replace it so this patch sends
> > lumpy reclaim to the farm.
> >
> > Here are the important notes related to the patch.
> >
> > 1. The tracepoint format changes for isolating LRU pages.
> >
> > 2. This patch stops reclaim/compaction entering sync reclaim as this
> >   was only intended for lumpy reclaim and an oversight. Page migration
> >   has its own logic for stalling on writeback pages if necessary and
> >   memory compaction is already using it. This is a behaviour change.
> >
> > 3. RECLAIM_MODE_SYNC no longer exists. pageout() does not stall
> >   on PageWriteback with CONFIG_COMPACTION has been this way for a while.
> >   I am calling it out in case this is a surpise to people.
> 
> Mel,
> 
> Can you point me the commit making that change? I am looking at
> v3.4-rc1 where set_reclaim_mode() still set RECLAIM_MODE_SYNC for
> COMPACTION_BUILD.
> 

You're right.

There is only one call site that passes sync==true for set_reclaim_mode() in
vmscan.c and that is only if should_reclaim_stall() returns true. It had the
comment "Only stall on lumpy reclaim" but the comment is not accurate
and that mislead me.

Thanks, I'll revisit the patch.

-- 
Mel Gorman
SUSE Labs
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