linux-kernel - Re: [PATCH] mm: __rmqueue_fallback() should respect pageblock type

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Message-Id: <20131030213537.f346d751.akpm@linux-foundation.org>
Date:	Wed, 30 Oct 2013 21:35:37 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	kosaki.motohiro@...il.com
Cc:	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	Mel Gorman <mgorman@...e.de>
Subject: Re: [PATCH] mm: __rmqueue_fallback() should respect pageblock type

On Thu, 31 Oct 2013 00:24:49 -0400 kosaki.motohiro@...il.com wrote:

> When __rmqueue_fallback() don't find out a free block with the same size
> of required, it splits a larger page and puts back rest peiece of the page
> to free list.
> 
> But it has one serious mistake. When putting back, __rmqueue_fallback()
> always use start_migratetype if type is not CMA. However, __rmqueue_fallback()
> is only called when all of start_migratetype queue are empty. That said,
> __rmqueue_fallback always put back memory to wrong queue except
> try_to_steal_freepages() changed pageblock type (i.e. requested size is
> smaller than half of page block). Finally, antifragmentation framework
> increase fragmenation instead of decrease.
> 
> Mel's original anti fragmentation do the right thing. But commit 47118af076
> (mm: mmzone: MIGRATE_CMA migration type added) broke it.
> 
> This patch restores sane and old behavior.

What are the user-visible runtime effects of this change?
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