Re: [PATCH -mm] mm: more likely reclaim MADV_SEQUENTIAL mappings

["KOSAKI Motohiro" <kosaki.motohiro@jp.fujitsu.com>]

Hi Johannes,

> File pages accessed only once through sequential-read mappings between
> fault and scan time are perfect candidates for reclaim.
>
> This patch makes page_referenced() ignore these singular references and
> the pages stay on the inactive list where they likely fall victim to the
> next reclaim phase.
>
> Already activated pages are still treated normally.  If they were
> accessed multiple times and therefor promoted to the active list, we
> probably want to keep them.
>
> Benchmarks show that big (relative to the system's memory)
> MADV_SEQUENTIAL mappings read sequentially cause much less kernel
> activity.  Especially less LRU moving-around because we never activate
> read-once pages in the first place just to demote them again.
>
> And leaving these perfect reclaim candidates on the inactive list makes
> it more likely for the real working set to survive the next reclaim
> scan.

looks good to me.
Actually, I made similar patch half year ago.

in my experience,
  - page_referenced_one is performance critical point.
    you should test some benchmark.
  - its patch improved mmaped-copy performance about 5%.
    (Of cource, you should test in current -mm. MM code was changed widely)

So, I'm looking for your test result :)

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