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SubjectRe: [PATCH v4] mm: incorporate read-only pages into transparent huge pages
On Thu, Jan 29, 2015 at 04:59:07PM +0200, Ebru Akagunduz wrote:
> This patch aims to improve THP collapse rates, by allowing
> THP collapse in the presence of read-only ptes, like those
> left in place by do_swap_page after a read fault.
> 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 applies the same limit for
> read-only ptes.
> 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 but 190MB of the program by
> touching other memory. Afterwards, the test program does
> a mix of reads and writes to its memory, and the memory
> gets swapped back in.
> Without the patch, only the memory that did not get
> swapped out remained in THPs, which corresponds to 24% of
> the memory of the program. The percentage did not increase
> over time.
> With this patch, after 5 minutes of waiting khugepaged had
> collapsed 60% of the program's memory back into THPs.
> Signed-off-by: Ebru Akagunduz <>
> Signed-off-by: Ebru Akagunduz <>
> Reviewed-by: Rik van Riel <>
> Acked-by: Vlastimil Babka <>
> Acked-by: Zhang Yanfei <>

Acked-by: Kirill A. Shutemov <>

Kirill A. Shutemov

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