linux-kernel - Re: [PATCH] mm: cache largest vma

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Message-ID: <5274114B.7010302@gmail.com>
Date:	Fri, 01 Nov 2013 16:38:35 -0400
From:	KOSAKI Motohiro <kosaki.motohiro@...il.com>
To:	Davidlohr Bueso <davidlohr@...com>,
	Andrew Morton <akpm@...ux-foundation.org>
CC:	kosaki.motohiro@...il.com, Hugh Dickins <hughd@...gle.com>,
	Michel Lespinasse <walken@...gle.com>,
	Ingo Molnar <mingo@...nel.org>, Mel Gorman <mgorman@...e.de>,
	Rik van Riel <riel@...hat.com>,
	Guan Xuetao <gxt@...c.pku.edu.cn>, aswin@...com,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [PATCH] mm: cache largest vma

(11/1/13 4:17 PM), Davidlohr Bueso wrote:
> While caching the last used vma already does a nice job avoiding
> having to iterate the rbtree in find_vma, we can improve. After
> studying the hit rate on a load of workloads and environments,
> it was seen that it was around 45-50% - constant for a standard
> desktop system (gnome3 + evolution + firefox + a few xterms),
> and multiple java related workloads (including Hadoop/terasort),
> and aim7, which indicates it's better than the 35% value documented
> in the code.
>
> By also caching the largest vma, that is, the one that contains
> most addresses, there is a steady 10-15% hit rate gain, putting
> it above the 60% region. This improvement comes at a very low
> overhead for a miss. Furthermore, systems with !CONFIG_MMU keep
> the current logic.

I'm slightly surprised this cache makes 15% hit. Which application
get a benefit? You listed a lot of applications, but I'm not sure
which is highly depending on largest vma.


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