Re: [RFC 3/3] mm: make swapin readahead to improve thp collapse rate
From: Rik van Riel
Date: Mon Jun 15 2015 - 10:00:10 EST
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@xxxxxxxxx>
Mechanism looks good to me.
Acked-by: Rik van Riel <riel@xxxxxxxxxx>
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