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Fri, 15 Aug 2025 10:52:20 -0700 (PDT) Received: from [127.0.0.1] ([185.70.53.184]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-45a233257b7sm13256305e9.3.2025.08.15.10.52.19 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 15 Aug 2025 10:52:20 -0700 (PDT) Date: Fri, 15 Aug 2025 21:52:17 +0400 From: gio To: Andrew Morton , zhongjinji@honor.com CC: linux-mm@kvack.org, mhocko@suse.com, rientjes@google.com, shakeel.butt@linux.dev, npache@redhat.com, linux-kernel@vger.kernel.org, tglx@linutronix.de, mingo@redhat.com, peterz@infradead.org, dvhart@infradead.org, dave@stgolabs.net, andrealmeid@igalia.com, liam.howlett@oracle.com, liulu.liu@honor.com, feng.han@honor.com Subject: =?US-ASCII?Q?Re=3A_=5BPATCH_v4_3/3=5D_mm/oom=5Fk?= =?US-ASCII?Q?ill=3A_Have_the_OOM_reaper_and?= =?US-ASCII?Q?_exit=5Fmmap=28=29_traverse_the_m?= =?US-ASCII?Q?aple_tree_in_opposite_orders?= User-Agent: Thunderbird for Android In-Reply-To: <20250814160914.7a4622ae1370092dde11c5f2@linux-foundation.org> References: <20250814135555.17493-1-zhongjinji@honor.com> <20250814135555.17493-4-zhongjinji@honor.com> <20250814160914.7a4622ae1370092dde11c5f2@linux-foundation.org> Message-ID: <1CAF2012-C9A4-44E1-BEB1-A1ECE0BC0C3E@gmail.com> MIME-Version: 1.0 Content-Type: multipart/alternative; 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charset=utf-8 Content-Transfer-Encoding: quoted-printable I believe the patch should be accepted=2E While the race condition might be= rare in simple workloads, it can become significant in containerized syste= ms or Android devices=2E The proposed solution is simple, low-risk, and dir= ectly addresses the identified problem with minimal code changes=2E On August 15, 2025 3:09:14 AM GMT+04:00, Andrew Morton wrote: >On Thu, 14 Aug 2025 21:55:55 +0800 wrote: > >> When a process is OOM killed, if the OOM reaper and the thread running >> exit_mmap() execute at the same time, both will traverse the vma's mapl= e >> tree along the same path=2E They may easily unmap the same vma, causing= them >> to compete for the pte spinlock=2E This increases unnecessary load, cau= sing >> the execution time of the OOM reaper and the thread running exit_mmap()= to >> increase=2E > >Please tell me what I'm missing here=2E > >OOM kills are a rare event=2E And this race sounds like it will rarely >occur even if an oom-killing is happening=2E And the delay will be >relatively short=2E > >If I'm correct then we're addressing rare*rare*small, so why bother? > >> When a process exits, exit_mmap() traverses the vma's maple tree from l= ow to high >> address=2E To reduce the chance of unmapping the same vma simultaneousl= y, >> the OOM reaper should traverse vma's tree from high to low address=2E T= his reduces >> lock contention when unmapping the same vma=2E > >Sharing some before-and-after runtime measurements would be useful=2E Or >at least, detailed anecdotes=2E > > ------OI3O6D1L05KWJSKQ8QZ9Y4YXUI62DW Content-Type: text/html; charset=utf-8 Content-Transfer-Encoding: quoted-printable
I believe the patch should be ac= cepted=2E While the race condition might be rare in simple workloads, it ca= n become significant in containerized systems or Android devices=2E The pro= posed solution is simple, low-risk, and directly addresses the identified p= roblem with minimal code changes=2E


On August 15, 2025 3:09:14 AM GMT+04:00, Andrew Morton &= lt;akpm@linux-foundation=2Eorg> wrote:
On Thu, 14 Aug 2025 21:55:55 +0800=
 <zhongjinji@honor=2Ecom> wrote:

When a process is OOM killed, i=
f the OOM reaper and the thread running
exit_mmap() execute at the same =
time, both will traverse the vma's maple
tree along the same path=2E The=
y may easily unmap the same vma, causing them
to compete for the pte spi=
nlock=2E This increases unnecessary load, causing
the execution time of =
the OOM reaper and the thread running exit_mmap() to
increase=2E

Please tell me what I'm missing here=
=2E

OOM kills are a rare event=2E  And this race sounds like it will=
 rarely
occur even if an oom-killing is happening=2E  And the delay will=
 be
relatively short=2E

If I'm correct then we're addressing rare=
*rare*small, so why bother?

When a process exits, exit_mmap() traverse=
s the vma's maple tree from low to high
address=2E To reduce the chance =
of unmapping the same vma simultaneously,
the OOM reaper should traverse=
 vma's tree from high to low address=2E This reduces
lock contention whe=
n unmapping the same vma=2E

Sha=
ring some before-and-after runtime measurements would be useful=2E  Or
a=
t least, detailed anecdotes=2E


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