linux-kernel - Re: [PATCH] mm/compaction: reset compaction scanner positions

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Date:	Mon, 23 Mar 2015 16:16:21 -0700 (PDT)
From:	David Rientjes <rientjes@...gle.com>
To:	Gioh Kim <gioh.kim@....com>
cc:	akpm@...ux-foundation.org, vbabka@...e.cz, iamjoonsoo.kim@....com,
	mgorman@...e.de, linux-mm@...ck.org, linux-kernel@...r.kernel.org,
	gunho.lee@....com, Gioh Kim <gioh.kim@....c>
Subject: Re: [PATCH] mm/compaction: reset compaction scanner positions

On Sat, 21 Mar 2015, Gioh Kim wrote:

> When the compaction is activated via /proc/sys/vm/compact_memory
> it would better scan the whole zone.
> And some platform, for instance ARM, has the start_pfn of a zone is zero.
> Therefore the first try to compaction via /proc doesn't work.
> It needs to force to reset compaction scanner position at first.
> 
> Signed-off-by: Gioh Kim <gioh.kim@....c>

That shouldn't be a valid email address.

> Acked-by: Vlastimil Babka <vbabka@...e.cz>

Acked-by: David Rientjes <rientjes@...gle.com>

I was thinking that maybe this would be better handled as part of the 
comapct_zone() logic, i.e. set cc->free_pfn and cc->migrate_pfn based on a 
helper function that understands cc->order == -1 should compact the entire 
zone.  However, after scanning the entire zone as a result of this write, 
the existing cached pfns probably don't matter anymore.  So this seems 
fine.
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