linux-kernel - Re: [PATCH v2] mm: incorporate zero pages into transparent huge pages

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Message-ID: <54E1D977.30004@suse.cz>
Date:	Mon, 16 Feb 2015 12:50:15 +0100
From:	Vlastimil Babka <vbabka@...e.cz>
To:	Ebru Akagunduz <ebru.akagunduz@...il.com>, linux-mm@...ck.org
CC:	akpm@...ux-foundation.org, kirill@...temov.name, mhocko@...e.cz,
	mgorman@...e.de, rientjes@...gle.com, sasha.levin@...cle.com,
	hughd@...gle.com, hannes@...xchg.org, linux-kernel@...r.kernel.org,
	riel@...hat.com, aarcange@...hat.com
Subject: Re: [PATCH v2] mm: incorporate zero pages into transparent huge pages

On 02/11/2015 10:03 PM, Ebru Akagunduz wrote:
> This patch improves THP collapse rates, by allowing zero pages.
> 
> Currently THP can collapse 4kB pages into a THP when there
> are up to khugepaged_max_ptes_none pte_none ptes in a 2MB
> range.  This patch counts pte none and mapped zero pages
> with the same variable.
> 
> The patch was tested with a program that allocates 800MB of
> memory, and performs interleaved reads and writes, in a pattern
> that causes some 2MB areas to first see read accesses, resulting
> in the zero pfn being mapped there.
> 
> To simulate memory fragmentation at allocation time, I modified
> do_huge_pmd_anonymous_page to return VM_FAULT_FALLBACK for read
> faults.
> 
> Without the patch, only %50 of the program was collapsed into
> THP and the percentage did not increase over time.
> 
> With this patch after 10 minutes of waiting khugepaged had
> collapsed %99 of the program's memory.
> 
> Signed-off-by: Ebru Akagunduz <ebru.akagunduz@...il.com>
> Reviewed-by: Rik van Riel <riel@...hat.com>

Acked-by: Vlastimil Babka <vbabka@...e.cz>

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