linux-kernel - Re: [RFC 3/3] mm: make swapin readahead to improve thp collapse rate

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Date:	Mon, 15 Jun 2015 09:59:47 -0400
From:	Rik van Riel <riel@...hat.com>
To:	Ebru Akagunduz <ebru.akagunduz@...il.com>, linux-mm@...ck.org
CC:	akpm@...ux-foundation.org, kirill.shutemov@...ux.intel.com,
	n-horiguchi@...jp.nec.com, aarcange@...hat.com,
	iamjoonsoo.kim@....com, xiexiuqi@...wei.com, gorcunov@...nvz.org,
	linux-kernel@...r.kernel.org, mgorman@...e.de, rientjes@...gle.com,
	vbabka@...e.cz, aneesh.kumar@...ux.vnet.ibm.com, hughd@...gle.com,
	hannes@...xchg.org, mhocko@...e.cz, boaz@...xistor.com,
	raindel@...lanox.com
Subject: Re: [RFC 3/3] mm: make swapin readahead to improve thp collapse rate

On 06/14/2015 11:04 AM, Ebru Akagunduz wrote:
> This patch makes swapin readahead to improve thp collapse rate.
> When khugepaged scanned pages, there can be a few of the pages
> in swap area.
> 
> With the patch THP can collapse 4kB pages into a THP when
> there are up to max_ptes_swap swap ptes in a 2MB range.
> 
> The patch was tested with a test program that allocates
> 800MB of memory, writes to it, and then sleeps. I force
> the system to swap out all. Afterwards, the test program
> touches the area by writing, it skips a page in each
> 20 pages of the area.
> 
> Without the patch, system did not swap in readahead.
> THP rate was %47 of the program of the memory, it
> did not change 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>

Mechanism looks good to me.

Acked-by: Rik van Riel <riel@...hat.com>

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