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

[Shakeel Butt <shakeel.butt@linux.dev>]

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@linux.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?