From: "Kirill A. Shutemov" <firstname.lastname@example.org> To: Michal Hocko <email@example.com> Cc: Daniel Colascione <firstname.lastname@example.org>, Qian Cai <email@example.com>, Tim Murray <firstname.lastname@example.org>, Suren Baghdasaryan <email@example.com>, firstname.lastname@example.org, linux-kernel <email@example.com>, linux-mm <firstname.lastname@example.org> Subject: Re: [PATCH] Make SPLIT_RSS_COUNTING configurable Date: Fri, 4 Oct 2019 16:26:24 +0300 [thread overview] Message-ID: <20191004132624.ctaodxaxsd7wzwlh@box> (raw) In-Reply-To: <20191004123349.GB10845@dhcp22.suse.cz> On Fri, Oct 04, 2019 at 02:33:49PM +0200, Michal Hocko wrote: > On Wed 02-10-19 19:08:16, Daniel Colascione wrote: > > On Wed, Oct 2, 2019 at 6:56 PM Qian Cai <email@example.com> wrote: > > > > On Oct 2, 2019, at 4:29 PM, Daniel Colascione <firstname.lastname@example.org> wrote: > > > > > > > > Adding the correct linux-mm address. > > > > > > > > > > > >> +config SPLIT_RSS_COUNTING > > > >> + bool "Per-thread mm counter caching" > > > >> + depends on MMU > > > >> + default y if NR_CPUS >= SPLIT_PTLOCK_CPUS > > > >> + help > > > >> + Cache mm counter updates in thread structures and > > > >> + flush them to visible per-process statistics in batches. > > > >> + Say Y here to slightly reduce cache contention in processes > > > >> + with many threads at the expense of decreasing the accuracy > > > >> + of memory statistics in /proc. > > > >> + > > > >> endmenu > > > > > > All those vague words are going to make developers almost impossible to decide the right selection here. It sounds like we should kill SPLIT_RSS_COUNTING at all to simplify the code as the benefit is so small vs the side-effect? > > > > Killing SPLIT_RSS_COUNTING would be my first choice; IME, on mobile > > and a basic desktop, it doesn't make a difference. I figured making it > > a knob would help allay concerns about the performance impact in more > > extreme configurations. > > I do agree with Qian. Either it is really helpful (is it? probably on > the number of cpus) and it should be auto-enabled or it should be > dropped altogether. You cannot really expect people know how to enable > this without a deep understanding of the MM internals. Not to mention > all those users using distro kernels/configs. > > A config option sounds like a bad way forward. And I don't see much point anyway. Reading RSS counters from proc is inherently racy. It can just either way after the read due to process behaviour. -- Kirill A. Shutemov
next prev parent reply other threads:[~2019-10-04 13:26 UTC|newest] Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top 2019-10-02 20:24 Daniel Colascione 2019-10-02 20:28 ` Daniel Colascione 2019-10-03 1:56 ` Qian Cai 2019-10-03 2:08 ` Daniel Colascione 2019-10-04 12:33 ` Michal Hocko 2019-10-04 13:26 ` Kirill A. Shutemov [this message] 2019-10-04 13:45 ` Daniel Colascione 2019-10-04 14:43 ` Michal Hocko 2019-10-07 0:11 ` Kirill A. Shutemov
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