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

From: Vlastimil Babka
Date: Mon Feb 16 2015 - 06:50:27 EST

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@xxxxxxxxx>
> Reviewed-by: Rik van Riel <riel@xxxxxxxxxx>

Acked-by: Vlastimil Babka <vbabka@xxxxxxx>

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