Re: [PATCH v2 2/2] mm/vmpressure: split v1 userspace eventfd code into vmpressure-v1.c

[Michal Koutný]

On Mon, Jun 29, 2026 at 02:55:57PM +0100, Usama Arif <usama.arif@xxxxxxxxx> wrote:
> On 29/06/2026 14:34, Michal Koutný wrote:
> > On Mon, Jun 29, 2026 at 05:59:37AM -0700, Usama Arif <usama.arif@xxxxxxxxx> wrote:
> >> 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
> > 
> > (Here I understand PSI is a different and differntly scope metric) but
> > what does it mean when you write that tree=false cannot be removed but
> > the other patch bails out from vmpressure() (i.e. nothing is updated
> > anyway)?
> So the first patch bails out for cgroup v2 for tree = true only.
> For tree = false, it doesn't bail out, and is still used for networking
> socket-buffer back-off. I think that is a whole another scope of work
> switching to PSI. Hope that makes sense?

I've mixed mutliple things together, sorry. I wanted to actually ask
about your response:

| I realized when trying to swap the order that the splitting off v1
| commit will end up doing more that what I think it should do (just
| splitting off v1 specific code), as the tree = true code will not get
| compiled in at all for cgroup v2, and it then ends up changing more
| behaviour.

tree=true won't get compiled but v2 doesn't care about it, so the effect
of patch 2/2 should still be same (regardless whether it comes 1st or
2nd).
Do you refer to the invocation of vmpressure_v1_account_tree() that is
affected by this?

Thanks,
Michal

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