linux-kernel - Re: [PATCH 7/7] mm: compaction: Introduce sync-light migration for use by compaction

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Date:	Wed, 23 Nov 2011 13:45:13 +0000
From:	Mel Gorman <mgorman@...e.de>
To:	Nai Xia <nai.xia@...il.com>
Cc:	Shaohua Li <shaohua.li@...el.com>, Linux-MM <linux-mm@...ck.org>,
	Andrea Arcangeli <aarcange@...hat.com>,
	Minchan Kim <minchan.kim@...il.com>, Jan Kara <jack@...e.cz>,
	Andy Isaacson <adi@...apodia.org>,
	Johannes Weiner <jweiner@...hat.com>,
	Rik van Riel <riel@...hat.com>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 7/7] mm: compaction: Introduce sync-light migration for
 use by compaction

On Wed, Nov 23, 2011 at 09:05:08PM +0800, Nai Xia wrote:
> > <SNIP>
> >
> > Where are you adding this check?
> >
> > If you mean in __unmap_and_move(), the check is unnecessary unless
> > another subsystem starts using sync-light compaction. With this series,
> > only direct compaction cares about MIGRATE_SYNC_LIGHT. If the page is
> 
> But I am still a little bit confused that if MIGRATE_SYNC_LIGHT is only
> used by direct compaction and  another mode can be used by it:
> MIGRATE_ASYNC also does not write dirty pages, then why not also
> do an (current->flags & PF_MEMALLOC) test before writing out pages,

Why would it be necessary?
Why would it be better than what is there now?

> like we already did for the page lock condition, but adding a new mode
> instead?
> 

I'm afraid I am missing the significance of your question or how it
might apply to the problem at hand.

-- 
Mel Gorman
SUSE Labs
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