linux-kernel - Re: [PATCH v3 2/2] selftests: vm: add COW time test for KSM pages

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Message-ID: <CA+CK2bB5kC=wVO0g4mC0VVFHhJyuoL_Kd7zqiHrmXC7jwejcWQ@mail.gmail.com>
Date:   Fri, 20 Aug 2021 13:20:04 -0400
From:   Pavel Tatashin <pasha.tatashin@...een.com>
To:     Tyler Hicks <tyhicks@...ux.microsoft.com>
Cc:     Zhansaya Bagdauletkyzy <zhansayabagdaulet@...il.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        linux-mm <linux-mm@...ck.org>, linux-kselftest@...r.kernel.org,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v3 2/2] selftests: vm: add COW time test for KSM pages

On Thu, Aug 19, 2021 at 12:31 PM Tyler Hicks
<tyhicks@...ux.microsoft.com> wrote:
>
> On 2021-08-19 21:33:43, Zhansaya Bagdauletkyzy wrote:
> > Since merged pages are copied every time they need to be modified,
> > the write access time is different between shared and non-shared pages.
> > Add ksm_cow_time() function which evaluates latency of these COW
> > breaks. First, 4000 pages are allocated and the time, required to modify
> > 1 byte in every other page, is measured. After this, the pages are
> > merged into 2000 pairs and in each pair, 1 page is modified (i.e. they
> > are decoupled) to detect COW breaks. The time needed to break COW of
> > merged pages is then compared with performance of non-shared pages.
> >
> > The test is run as follows: ./ksm_tests -C
> > The output:
> >       Total size:    15 MiB
> >
> >       Not merged pages:
> >       Total time:     0.002185489 s
> >       Average speed:  3202.945 MiB/s
> >
> >       Merged pages:
> >       Total time:     0.004386872 s
> >       Average speed:  1595.670 MiB/s
> >
> > Signed-off-by: Zhansaya Bagdauletkyzy <zhansayabagdaulet@...il.com>
> > ---
> > v2 -> v3:
> >  - address Tyler's feedback
>
> Thanks for incorporating my suggestions! I can confirm that my feedback
> was completely addressed.
>
>  Reviewed-by: Tyler Hicks <tyhicks@...ux.microsoft.com>
>
> Tyler

Reviewed-by: Pavel Tatashin <pasha.tatashin@...een.com>