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

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Message-ID: <CAK1f24kL_XHsOJ-m30t17bSBnV9wpam33Hmcpf7baT87Yt5FrA@mail.gmail.com>
Date: Thu, 22 Feb 2024 17:12:00 +0800
From: Lance Yang <ioworker0@...il.com>
To: David Hildenbrand <david@...hat.com>
Cc: akpm@...ux-foundation.org, 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

Thanks, David!

On Thu, Feb 22, 2024 at 4:51 PM David Hildenbrand <david@...hat.com> wrote:
>
> 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
>