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

[Suren Baghdasaryan]

On Wed, Sep 10, 2025 at 1:10 PM Shakeel Butt <shakeel.butt@xxxxxxxxx> wrote:
>
> 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@xxxxxxxxx> 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.

Yes, cgroups v2 with per-app hierarchy is already enabled on Android
as of about a year or so ago. The first usecase was the freezer. TJ
(CC'ing him here) also changed how ActivityManager Service (AMS) kills
process groups to use cgroup.kill (think when you force-stop an app
that's what will happen). LMKD has not been changed to use cgroup.kill
but that might be worth doing now. TJ, WDYT?


> > >