linux-kernel - Re: [PATCH v2] mm: Warn about costly page allocation

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Date:	Wed, 11 Jul 2012 16:02:00 -0700 (PDT)
From:	David Rientjes <rientjes@...gle.com>
To:	Minchan Kim <minchan@...nel.org>
cc:	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	Rik van Riel <riel@...hat.com>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	Mel Gorman <mgorman@...e.de>,
	Johannes Weiner <hannes@...xchg.org>,
	Kamezawa Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
Subject: Re: [PATCH v2] mm: Warn about costly page allocation

On Thu, 12 Jul 2012, Minchan Kim wrote:

> There is QA team in embedded company and they have tested their product.
> In test scenario, they can allocate 100 high order allocation.
> (they don't matter how many high order allocations in kernel are needed
> during test. their concern is just only working well or fail of their
> middleware/application) High order allocation will be serviced well
> by natural buddy allocation without lumpy's help. So they released
> the product and sold out all over the world.
> Unfortunately, in real practice, sometime, 105 high order allocation was
> needed rarely and fortunately, lumpy reclaim could help it so the product
> doesn't have a problem until now.
> 

If the QA team is going to consider upgrading to a kernel since lumpy 
reclaim has been removed, before they qualify such a kernel they would 
(hopefully) do some due diligence in running this workload and noticing 
the page allocation failure that is emitted to the kernel log for the high 
order page allocations.

> If they use latest kernel, they will see the new config CONFIG_COMPACTION
> which is very poor documentation, and they can't know it's replacement of
> lumpy reclaim(even, they don't know lumpy reclaim) so they simply disable
> that option for size optimization.

Improving the description for CONFIG_COMPACTION or adding additional 
documentation in Documentation/vm would be very appreciated by both me and 
this hypothetical engineer :)
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