linux-kernel - Re: [PATCH 1/1] mm/khugepaged: bypassing unnecessary scans with MMF_DISABLE

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Message-ID: <84fc211a-075d-44c7-a4c3-698931b6dc7c@redhat.com>
Date: Thu, 22 Feb 2024 09:51:00 +0100
From: David Hildenbrand <david@...hat.com>
To: Lance Yang <ioworker0@...il.com>, akpm@...ux-foundation.org
Cc: mhocko@...e.com, zokeefe@...gle.com, songmuchun@...edance.com,
 shy828301@...il.com, peterx@...hat.com, minchan@...nel.org,
 linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/1] mm/khugepaged: bypassing unnecessary scans with
 MMF_DISABLE_THP check

On 22.02.24 08:51, Lance Yang wrote:
> Hey,
> 
> On an Intel Core i5 CPU, the time taken by
> khugepaged to scan the address space of
> the process, which has been set with the
> MMF_DISABLE_THP flag after being added
> to the mm_slots list, is as follows (shorter is better):
> 
> VMA Count |   Old   |   New   |  Change
> ---------------------------------------
>      50     |   23us  |    9us  |  -60.9%
>     100     |   32us  |    9us  |  -71.9%
>     200     |   44us  |    9us  |  -79.5%
>     400     |   75us  |    9us  |  -88.0%
>     800     |   98us  |    9us  |  -90.8%
> 
> IIUC, once the count of VMAs for the process
> exceeds page_to_scan, khugepaged needs to
> wait for scan_sleep_millisecs ms before scanning
> the next process. IMO, unnecessary scans could
> actually be skipped with a very inexpensive
> mm->flags check in this case.

FWIW

Acked-by: David Hildenbrand <david@...hat.com>

-- 
Cheers,

David / dhildenb