Re: [PATCH 0/2] mm/vmpressure: reduce CPU, memory and code overhead on cgroup v2

[Usama Arif <usama.arif@linux.dev>]

On 08/06/2026 20:56, Shakeel Butt wrote:
> On Mon, Jun 08, 2026 at 07:49:45PM +0100, Usama Arif wrote:
>>
>>
>>>
>>> For this, I am wondering if we should just go ahead and work towards making
>>> vmpressure memcg-v1 only unless we foresee a lot of or complex work is needed
>>> for that and only then patch 2 makes sense.
>>>
>>
>> I think there might be a transition needed? Because vmpressure and PSI
>> do not work out to be the same and people might notice a regression with
>> increased memory usage or a hit in networking performance and might want to
>> opt out? A solution might be to switch socket pressure to PSI while
>> keeping vmpressure around gated by a defconfig. And then in a few releases
>> remove it completely for cgroup v2 if no one complaints. If we go down that
>> path, we would need patch 2 for the medium term.
> 
> Yeah the reasoning that PSI is not an exact replacement for vmpressure makes
> sense and it will take couple of iterations to transition v2 (networking) away
> from vmpressure. Can you please update your commit message with this and about
> the midterm or transition plan.
> 
> I assume eventually we will just have vmpressure-v1.c file which will be behind
> MEMCG_V1 flag, correct?

Yes.

How about something like below in the commit message? :

This split is the first step toward eventually making vmpressure
CONFIG_MEMCG_V1 only. The v2 in-kernel socket pressure path
(tree=false) cannot be removed today immediately: PSI is not an
exact replacement for vmpressure, and switching networking socket-buffer
back-off to PSI may regress networking performance or increase memory pressure
in workloads that today rely on vmpressure's hysteresis. The medium-term plan is
to introduce a PSI-based socket-pressure path, keep vmpressure available for
v2 behind a defconfig as an opt-out for several releases, and only then
drop the tree=false path entirely, at which point everything that
remains in mm/vmpressure-v1.c is the whole subsystem.