linux-kernel - Re: [PATCH v0 0/2] mm: swap: Gather swap entries and batch async release

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Message-ID: <qisfqncqgkgxh2nj5axafunlfjen6oiciobcrmpus6l3xwrbyj@blxv73pbhzez>
Date: Wed, 10 Sep 2025 13:10:46 -0700
From: Shakeel Butt <shakeel.butt@...ux.dev>
To: Suren Baghdasaryan <surenb@...gle.com>
Cc: Lei Liu <liulei.rjpt@...o.com>, Michal Hocko <mhocko@...e.com>, 
	David Rientjes <rientjes@...gle.com>, Andrew Morton <akpm@...ux-foundation.org>, 
	Kemeng Shi <shikemeng@...weicloud.com>, Kairui Song <kasong@...cent.com>, Nhat Pham <nphamcs@...il.com>, 
	Baoquan He <bhe@...hat.com>, Barry Song <baohua@...nel.org>, Chris Li <chrisl@...nel.org>, 
	Johannes Weiner <hannes@...xchg.org>, Roman Gushchin <roman.gushchin@...ux.dev>, 
	Muchun Song <muchun.song@...ux.dev>, David Hildenbrand <david@...hat.com>, 
	Lorenzo Stoakes <lorenzo.stoakes@...cle.com>, "Liam R. Howlett" <Liam.Howlett@...cle.com>, 
	Vlastimil Babka <vbabka@...e.cz>, Mike Rapoport <rppt@...nel.org>, 
	Brendan Jackman <jackmanb@...gle.com>, Zi Yan <ziy@...dia.com>, 
	"Peter Zijlstra (Intel)" <peterz@...radead.org>, Chen Yu <yu.c.chen@...el.com>, Hao Jia <jiahao1@...iang.com>, 
	"Kirill A. Shutemov" <kas@...nel.org>, Usama Arif <usamaarif642@...il.com>, 
	Oleg Nesterov <oleg@...hat.com>, Christian Brauner <brauner@...nel.org>, 
	Mateusz Guzik <mjguzik@...il.com>, Steven Rostedt <rostedt@...dmis.org>, 
	Andrii Nakryiko <andrii@...nel.org>, Al Viro <viro@...iv.linux.org.uk>, 
	Fushuai Wang <wangfushuai@...du.com>, "open list:MEMORY MANAGEMENT - OOM KILLER" <linux-mm@...ck.org>, 
	open list <linux-kernel@...r.kernel.org>, 
	"open list:CONTROL GROUP - MEMORY RESOURCE CONTROLLER (MEMCG)" <cgroups@...r.kernel.org>
Subject: Re: [PATCH v0 0/2] mm: swap: Gather swap entries and batch async
 release

On Tue, Sep 09, 2025 at 12:48:02PM -0700, Suren Baghdasaryan wrote:
> On Tue, Sep 9, 2025 at 12:21 PM Shakeel Butt <shakeel.butt@...ux.dev> wrote:
> >
> > On Tue, Sep 09, 2025 at 02:53:39PM +0800, Lei Liu wrote:
> > > 1. Problem Scenario
> > > On systems with ZRAM and swap enabled, simultaneous process exits create
> > > contention. The primary bottleneck occurs during swap entry release
> > > operations, causing exiting processes to monopolize CPU resources. This
> > > leads to scheduling delays for high-priority processes.
> > >
> > > 2. Android Use Case
> > > During camera launch, LMKD terminates background processes to free memory.
> >
> > How does LMKD trigger the kills? SIGKILL or cgroup.kill?
> 
> SIGKILL
> 
> >
> > > Exiting processes compete for CPU cycles, delaying the camera preview
> > > thread and causing visible stuttering - directly impacting user
> > > experience.
> >
> > Since the exit/kill is due to low memory situation, punting the memory
> > freeing to a low priority async mechanism will help in improving user
> > experience. Most probably the application (camera preview here) will get
> > into global reclaim and will compete for CPU with the async memory
> > freeing.
> >
> > What we really need is faster memory freeing and we should explore all
> > possible ways. As others suggested fix/improve the bottleneck in the
> > memory freeing path. In addition I think we should explore parallelizing
> > this as well.
> >
> > On Android, I suppose most of the memory is associated with single or
> > small set of processes and parallelizing memory freeing would be
> > challenging. BTW is LMKD using process_mrelease() to release the killed
> > process memory?
> 
> Yes, LMKD has a reaper thread which wakes up and calls
> process_mrelease() after the main LMKD thread issued SIGKILL.
> 

Thanks Suren. I remember Android is planning to use Apps in cgroup. Is
that still the plan? I am actually looking into cgroup.kill, beside
sending SIGKILL, putting the processes of the target cgroup in the oom
reaper list. In addition, making oom reaper able to reap processes in
parallel. I am hoping that functionality to be useful to Android as
well.
> >