Re: [PATCH 1/1] mm: prevent a race between process_mrelease and exit_mmap

From: Suren Baghdasaryan <surenb@google.com>
To: Matthew Wilcox <willy@infradead.org>
Cc: "Liam R. Howlett" <liam.howlett@oracle.com>,
	Michal Hocko <mhocko@suse.com>,
	Andrew Morton <akpm@linux-foundation.org>,
	David Rientjes <rientjes@google.com>,
	Johannes Weiner <hannes@cmpxchg.org>,
	Roman Gushchin <guro@fb.com>, Rik van Riel <riel@surriel.com>,
	Minchan Kim <minchan@kernel.org>,
	Christian Brauner <christian@brauner.io>,
	Christoph Hellwig <hch@infradead.org>,
	Oleg Nesterov <oleg@redhat.com>,
	David Hildenbrand <david@redhat.com>,
	Jann Horn <jannh@google.com>, Shakeel Butt <shakeelb@google.com>,
	Andy Lutomirski <luto@kernel.org>,
	Christian Brauner <christian.brauner@ubuntu.com>,
	Florian Weimer <fweimer@redhat.com>,
	Jan Engelhardt <jengelh@inai.de>,
	Linux API <linux-api@vger.kernel.org>,
	linux-mm <linux-mm@kvack.org>,
	LKML <linux-kernel@vger.kernel.org>,
	kernel-team <kernel-team@android.com>,
	"Kirill A. Shutemov" <kirill@shutemov.name>,
	Andrea Arcangeli <aarcange@redhat.com>
Subject: Re: [PATCH 1/1] mm: prevent a race between process_mrelease and exit_mmap
Date: Wed, 27 Oct 2021 11:00:38 -0700	[thread overview]
Message-ID: <CAJuCfpH6ZGc9qaG6cNsJhHTaKdf_EXQgX7iRRcqXF6GiL-Mj8Q@mail.gmail.com> (raw)
In-Reply-To: <YXmRq5d86Umzrxs+@casper.infradead.org>

On Wed, Oct 27, 2021 at 10:52 AM Matthew Wilcox <willy@infradead.org> wrote:
>
> On Wed, Oct 27, 2021 at 10:42:29AM -0700, Suren Baghdasaryan wrote:
> > On Wed, Oct 27, 2021 at 10:35 AM Matthew Wilcox <willy@infradead.org> wrote:
> > >
> > > On Wed, Oct 27, 2021 at 09:08:21AM -0700, Suren Baghdasaryan wrote:
> > > > Unconditional mmap_write_lock around free_pgtables in exit_mmap seems
> > > > to me the most semantically correct way forward and the pushback is on
> > > > the basis of regressing performance of the exit path. I would like to
> > > > measure that regression to confirm this. I don't have access to a big
> > > > machine but will ask someone in another Google team to try the test
> > > > Michal wrote here
> > > > https://lore.kernel.org/all/20170725142626.GJ26723@dhcp22.suse.cz/ on
> > > > a server with and without a custom patch.
> > >
> > > Sorry to hijack this, but could you ask that team to also test this
> > > patch?  I think there's probably a good-sized win here, but I have no
> > > profiles to share at this point.  I've only done light testing, and
> > > it may have bugs.
> > >
> > > NB: I only did the exit() path here.  fork() conversion is left as an
> > > exercise for the reader^W^W Liam.
> >
> > To clarify, this patch does not change the mmap_write_lock portion of
> > exit_mmap. Do you want to test it in isolation or with the locking
> > changes in exit_mmap I mentioned?
>
> Correct, it does not.  I think it's interesting to test it in isolation,
> but if you want to test it in in combination, that could also be
> interesting (see if we regain some of the expected performance loss).
> I just don't have a NUMA box of my own to test on, so I'm hoping to
> exploit your test infrastructure ;-)
>
> By the way, my vmavec patch should also be helpful on small systems
> like phones ... ;-)

Sounds good. I'll try to queue up the patches so that it's easy to
test them both in isolation and together.