linux-kernel - Re: [PATCH v7 2/2] mm/oom_kill: The OOM reaper traverses the VMA maple tree in reverse order

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Message-ID: <aLqrYbsLzdr8tXe7@tiehlicka>
Date: Fri, 5 Sep 2025 11:20:33 +0200
From: Michal Hocko <mhocko@...e.com>
To: "Liam R. Howlett" <Liam.Howlett@...cle.com>
Cc: zhongjinji <zhongjinji@...or.com>, rientjes@...gle.com,
	shakeel.butt@...ux.dev, akpm@...ux-foundation.org,
	linux-mm@...ck.org, linux-kernel@...r.kernel.org,
	tglx@...utronix.de, lorenzo.stoakes@...cle.com, surenb@...gle.com,
	liulu.liu@...or.com, feng.han@...or.com
Subject: Re: [PATCH v7 2/2] mm/oom_kill: The OOM reaper traverses the VMA
 maple tree in reverse order

On Thu 04-09-25 22:12:48, Liam R. Howlett wrote:
> * Michal Hocko <mhocko@...e.com> [250904 08:21]:
> > On Wed 03-09-25 15:02:34, Liam R. Howlett wrote:
> > > * Michal Hocko <mhocko@...e.com> [250903 08:58]:
> > > > On Wed 03-09-25 17:27:29, zhongjinji wrote:
> > [...]
> > > mmu_notifier_release(mm) is called early in the exit_mmap() path should
> > > cause the mmu notifiers to be non-blocking (according to the comment in
> > > v6.0 source of exit_mmap [1].
> > 
> > I am not sure I follow you here. How does this relate to the actual
> > direction of the address space freeing?
> 
> It doesn't relate to the direction of the address freeing, I think it
> explains the perf data a bit.
> 
> The exit_mmap() would have a decrease in mmu related work while this
> thread will have an increase, I think.
> 
> If they race, this thread gets virtually nothing while exit does all of
> the work.  If they don't race then the work is split.
> 
> Does that make sense?

OK, I can see what you mean now. Thanks! I believe we need more data to
understand what is actually going on here. Having the overall duration
should help to get that.

-- 
Michal Hocko
SUSE Labs