linux-kernel - Re: [PATCH] mm, page_alloc: optimize batch count in free_pcppages

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Date:	Thu, 8 Aug 2013 04:08:16 +0900
From:	JoonSoo Kim <js1304@...il.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Joonsoo Kim <iamjoonsoo.kim@....com>,
	Linux Memory Management List <linux-mm@...ck.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Minchan Kim <minchan@...nel.org>,
	Johannes Weiner <hannes@...xchg.org>,
	Mel Gorman <mgorman@...e.de>, Rik van Riel <riel@...hat.com>
Subject: Re: [PATCH] mm, page_alloc: optimize batch count in free_pcppages_bulk()

Hello, Andrew.

2013/8/7 Andrew Morton <akpm@...ux-foundation.org>:
> On Tue,  6 Aug 2013 17:40:40 +0900 Joonsoo Kim <iamjoonsoo.kim@....com> wrote:
>
>> If we use a division operation, we can compute a batch count more closed
>> to ideal value. With this value, we can finish our job within
>> MIGRATE_PCPTYPES iteration. In addition, batching to free more pages
>> may be helpful to cache usage.
>>
>
> hm, maybe.  The .text got 120 bytes larger so the code now will
> eject two of someone else's cachelines, which can't be good.  I need
> more convincing, please ;)
>
> (bss got larger too - I don't have a clue why this happens).

In my testing, it makes .text just 64 byes larger.
I think that I cannot avoid such few increasing size.

Current round-robin freeing algorithm access 'struct page' at random
order, because
it change it's migrate type and list on every iteration and a page on
different list
may be far from each other. If we do more batch free, we have more
probability to access
adjacent 'struct page' than before, so I think that this is
cache-friendly. But this is just
theoretical argument, so I'm not sure whether it is useful or not :)

Thanks.
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