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

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Message-ID: <CAJuCfpFVUOLtmJyo_B+Z6HAaDOfuZhYZX71EpQW3+dpQhm3EQw@mail.gmail.com>
Date: Wed, 10 Sep 2025 07:56:09 -0700
From: Suren Baghdasaryan <surenb@...gle.com>
To: Lei Liu <liulei.rjpt@...o.com>
Cc: Shakeel Butt <shakeel.butt@...ux.dev>, 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 7:14 AM Lei Liu <liulei.rjpt@...o.com> 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.

I wasn't really suggesting anything, just explaining how LMKD works today.

>
>
> Thank you
>
>
>
>
> >