Re: [PATCH v3] memcg: expose socket memory pressure in a cgroup

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

On Wed, Jul 23, 2025 at 10:58:10AM +0200, Daniel Sedlak wrote:
> On 7/23/25 10:38 AM, Michal Koutný wrote:
> > On Tue, Jul 22, 2025 at 01:11:05PM -0700, Shakeel Butt <shakeel.butt@linux.dev> wrote:
> > > > > 1 second is the current implementation and it can be more if the memcg
> > > > > remains in memory pressure. Regarding usefullness I think the periodic
> > > > > stat collectors (like cadvisor or Google's internal borglet+rumbo) would
> > > > > be interested in scraping this interface.
> > > > 
> > > > I think the cumulative counter suggested above is better at least.
> > > 
> > > It is tied to the underlying implementation. If we decide to use, for
> > > example, PSI in future, what should this interface show?
> > 
> > Actually, if it was exposed as cummulative time under pressure (not
> > cummulative events), that's quite similar to PSI.
> 
> I think overall the cumulative counter is better than just signaling 1 or 0,
> but it lacks the time information (if not scraped periodically). In
> addition, it may oscillate between under_pressure=true/false rather quickly
> so the cumulative counter would catch this.

Yes cumulative counter would not miss small bursts.

> 
> To me, introducing the new PSI for sockets (like for CPU, IO, memory), would
> be slightly better than cumulative counter because PSI can have the timing
> information without frequent periodic scrapes. So it may help with live
> debugs.

How would this PSI for sockets work? What would be the entry and exit
points?

> 
> However, if we were to just add a new counter to the memory.stat in each
> cgroup, then it would be easier to do so?