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

From: Andrew Morton
Date: Thu Oct 31 2013 - 00:34:34 EST

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