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

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Message-ID: <uwqrobr5xqtvav73srbe6v2nccgtoy2456vpgzemwex26lwsq7@2g74vl5oomfx>
Date: Wed, 10 Sep 2025 13:12:00 -0700
From: Shakeel Butt <shakeel.butt@...ux.dev>
To: Lei Liu <liulei.rjpt@...o.com>
Cc: Suren Baghdasaryan <surenb@...gle.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 Wed, Sep 10, 2025 at 10:14:04PM +0800, Lei Liu wrote:
> 
> On 2025/9/10 3:48, 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.
> 
> Hi Suren
> 
> our current issue is that after lmkd kills a process,|exit_mm|takes
> considerable time. The interface you provided might help quickly free
> memory, potentially allowing us to release some memory from processes before
> lmkd kills them. This could be a good idea.
> 
> We will take your suggestion into consideration.

But LMKD already does the process_mrelease(). Is that not happening on
your setup?