Re: [RFC v5 3/3] mm: make swapin readahead to improve thp collapse rate
From: Kirill A. Shutemov <hidden>
Date: 2015-09-17 15:13:32
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memory management, memory management - thp (transparent huge page), the rest · Maintainers:
Andrew Morton, David Hildenbrand, Lorenzo Stoakes, Linus Torvalds
On Mon, Sep 14, 2015 at 10:31:45PM +0300, 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 400B 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 %65 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 <redacted> Acked-by: Rik van Riel <redacted>
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