From: Suren Baghdasaryan <surenb@google.com>
To: Andrew Morton <akpm@linux-foundation.org>
Cc: Michal Hocko <mhocko@kernel.org>,
David Rientjes <rientjes@google.com>,
Matthew Wilcox <willy@infradead.org>,
Johannes Weiner <hannes@cmpxchg.org>,
Roman Gushchin <guro@fb.com>, Rik van Riel <riel@surriel.com>,
Christian Brauner <christian@brauner.io>,
Oleg Nesterov <oleg@redhat.com>,
Tim Murray <timmurray@google.com>,
linux-api@vger.kernel.org, linux-mm <linux-mm@kvack.org>,
LKML <linux-kernel@vger.kernel.org>,
kernel-team <kernel-team@android.com>,
Minchan Kim <minchan@kernel.org>
Subject: Re: [PATCH 1/1] RFC: add pidfd_send_signal flag to reclaim mm while killing a process
Date: Fri, 13 Nov 2020 17:57:02 -0800 [thread overview]
Message-ID: <CAJuCfpH-Qjm5uqfaUcfk0QV2zC76uL96FQjd88bZGBvCuXE_aA@mail.gmail.com> (raw)
In-Reply-To: <20201113171810.bebf66608b145cced85bf54c@linux-foundation.org>
On Fri, Nov 13, 2020 at 5:18 PM Andrew Morton <akpm@linux-foundation.org> wrote:
>
> On Fri, 13 Nov 2020 17:09:37 -0800 Suren Baghdasaryan <surenb@google.com> wrote:
>
> > > > > Seems to me that the ability to reap another process's memory is a
> > > > > generally useful one, and that it should not be tied to delivering a
> > > > > signal in this fashion.
> > > > >
> > > > > And we do have the new process_madvise(MADV_PAGEOUT). It may need a
> > > > > few changes and tweaks, but can't that be used to solve this problem?
> > > >
> > > > Thank you for the feedback, Andrew. process_madvise(MADV_DONTNEED) was
> > > > one of the options recently discussed in
> > > > https://lore.kernel.org/linux-api/CAJuCfpGz1kPM3G1gZH+09Z7aoWKg05QSAMMisJ7H5MdmRrRhNQ@mail.gmail.com
> > > > . The thread describes some of the issues with that approach but if we
> > > > limit it to processes with pending SIGKILL only then I think that
> > > > would be doable.
> > >
> > > Why would it be necessary to read /proc/pid/maps? I'd have thought
> > > that a starting effort would be
> > >
> > > madvise((void *)0, (void *)-1, MADV_PAGEOUT)
> > >
> > > (after translation into process_madvise() speak). Which is equivalent
> > > to the proposed process_madvise(MADV_DONTNEED_MM)?
> >
> > Yep, this is very similar to option #3 in
> > https://lore.kernel.org/linux-api/CAJuCfpGz1kPM3G1gZH+09Z7aoWKg05QSAMMisJ7H5MdmRrRhNQ@mail.gmail.com
> > and I actually have a tested prototype for that.
>
> Why is the `vector=NULL' needed? Can't `vector' point at a single iovec
> which spans the whole address range?
That would be the option #4 from the same discussion and the issues
noted there are "process_madvise return value can't handle such a
large number of bytes and there is MAX_RW_COUNT limit on max number of
bytes one process_madvise call can handle". In my prototype I have a
special handling for such "bulk operation" to work around the
MAX_RW_COUNT limitation.
>
> > If that's the
> > preferred method then I can post it quite quickly.
>
> I assume you've tested that prototype. How did its usefulness compare
> with this SIGKILL-based approach?
Just to make sure I understand correctly your question, you are asking
about performance comparison of:
// approach in this RFC
pidfd_send_signal(SIGKILL, SYNC_REAP_MM)
vs
// option #4 in the previous RFC
kill(SIGKILL); process_madvise(vector=NULL, MADV_DONTNEED);
If so, I have results for the current RFC approach but the previous
approach was testing on an older device, so don't have
apples-to-apples comparison results at the moment. I can collect the
data for fair comparison if desired, however I don't expect a
noticeable performance difference since they both do pretty much the
same thing (even on different devices my results are quite close). I
think it's more a question of which API would be more appropriate.
>
next prev parent reply other threads:[~2020-11-14 1:57 UTC|newest]
Thread overview: 18+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-11-13 17:34 [PATCH 1/1] RFC: add pidfd_send_signal flag to reclaim mm while killing a process Suren Baghdasaryan
2020-11-13 23:55 ` Andrew Morton
2020-11-14 0:06 ` Suren Baghdasaryan
2020-11-14 1:00 ` Andrew Morton
2020-11-14 1:09 ` Suren Baghdasaryan
2020-11-14 1:18 ` Andrew Morton
2020-11-14 1:57 ` Suren Baghdasaryan [this message]
2020-11-14 2:16 ` Andrew Morton
2020-11-14 2:51 ` Suren Baghdasaryan
2020-11-16 23:24 ` Minchan Kim
2020-11-18 19:10 ` Michal Hocko
2020-11-18 19:22 ` Suren Baghdasaryan
2020-11-18 19:32 ` Michal Hocko
2020-11-18 19:51 ` Suren Baghdasaryan
2020-11-18 19:55 ` Suren Baghdasaryan
2020-11-19 0:13 ` Suren Baghdasaryan
2020-11-24 5:45 ` Suren Baghdasaryan
2020-11-18 10:32 ` Christian Brauner
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