From: "Michael Kerrisk (man-pages)" <mtk.manpages@gmail.com>
To: Jann Horn <jannh@google.com>
Cc: mtk.manpages@gmail.com, linux-man <linux-man@vger.kernel.org>,
Linux-MM <linux-mm@kvack.org>,
Mark Mossberg <mark.mossberg@gmail.com>,
Michal Hocko <mhocko@suse.com>
Subject: Re: [PATCH] proc.5: Document inaccurate RSS due to SPLIT_RSS_COUNTING
Date: Tue, 27 Oct 2020 14:49:14 +0100 [thread overview]
Message-ID: <b979d164-1abc-0be9-50a0-0548978c627f@gmail.com> (raw)
In-Reply-To: <CAG48ez2gigjfi3_nmbyhDnb2bsi9K0Yc24y7HdSNDvtumWGbiw@mail.gmail.com>
On 10/27/20 11:35 AM, Jann Horn wrote:
> On Tue, Oct 27, 2020 at 8:05 AM Michael Kerrisk (man-pages)
> <mtk.manpages@gmail.com> wrote:
>> On 10/12/20 4:52 PM, Jann Horn wrote:
>>> On Mon, Oct 12, 2020 at 1:49 PM Jann Horn <jannh@google.com> wrote:
>>>> Since 34e55232e59f7b19050267a05ff1226e5cd122a5 (introduced back in
>>>> v2.6.34), Linux uses per-thread RSS counters to reduce cache contention on
>>>> the per-mm counters. With a 4K page size, that means that you can end up
>>>> with the counters off by up to 252KiB per thread.
>>>
>>> Actually, as Mark Mossberg pointed out to me off-thread, the counters
>>> can actually be off by many times more...
>>
>> So, does your patch to proc.5 need tweaking, or can I just apply as is?
>
> The "(up to 63 pages per thread)" would have to go, the rest should be correct.
>
> But as Michal said, if someone volunteers to get rid of this
> optimization, maybe we don't need the documentation after all? But
> that would probably require actually doing some careful
> heavily-multithreaded benchmarking on a big machine with a few dozen
> cores, or something like that, so that we know whether this
> optimization actually is unimportant enough that we can just get rid
> of it...
Okay -- in the meantime, I've applied your patch, with your
suggested edit, to remove "(up to 63 pages per thread)".
Thanks!
Cheers,
Michael
--
Michael Kerrisk
Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/
Linux/UNIX System Programming Training: http://man7.org/training/
next prev parent reply other threads:[~2020-10-27 13:49 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-10-12 11:49 [PATCH] proc.5: Document inaccurate RSS due to SPLIT_RSS_COUNTING Jann Horn
2020-10-12 14:52 ` Jann Horn
2020-10-27 7:05 ` Michael Kerrisk (man-pages)
2020-10-27 10:35 ` Jann Horn
2020-10-27 12:18 ` Michal Hocko
2020-10-27 13:49 ` Michal Hocko
2020-10-27 13:49 ` Michael Kerrisk (man-pages) [this message]
2020-10-12 15:07 ` Michal Hocko
2020-10-12 15:20 ` Jann Horn
2020-10-12 15:33 ` Michal Hocko
2020-10-27 18:56 ` Vlastimil Babka
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