Re: [PATCH] memcg: Keep socket_pressure fresh on 32-bit kernel.

[Andrew Morton <akpm@linux-foundation.org>]

On Wed, 16 Jul 2025 16:58:29 -0700 Kuniyuki Iwashima <kuniyu@google.com> wrote:

> On Wed, Jul 16, 2025 at 4:52 PM Andrew Morton <akpm@linux-foundation.org> wrote:
> >
> > On Wed, 16 Jul 2025 16:13:54 -0700 Kuniyuki Iwashima <kuniyu@google.com> wrote:
> >
> > > > > Thus, we need to update socket_pressure to a recent timestamp
> > > > > periodically on 32-bit kernel.
> > > > >
> > > > > Let's do that every 24 hours, with a variation of about 0 to 4 hours.
> > > >
> > > > Can't we simply convert ->socket_preesure to a 64-bit type?
> > > > timespec64/time64_t/etc?
> > >
> > > I think it's doable with get_jiffies_64() & time_before64().
> > >
> > > My thought was a delayed work would be better than adding
> > > two seqlock in the networking fast path.
> >
> > Is it on a very fast path?  mem_cgroup_under_socket_pressure() itself
> > doesn't look very fastpath-friendly and seqcounts are fast.  Bearing in
> > mind that this affects 32-bit machines only.
> >
> > If a get_jiffies_64() call is demonstrated to be a performance issue
> > then perhaps there's something sneaky we can do along the lines of
> > reading jiffies_64 directly then falling back to get_jiffies_64() in
> > the rare something-went-wrong path.  Haven't thought about it :)
> >
> > Dunno, the proposed patch just feels like overkill for a silly
> > 32/66-bit issue?
> 
> Fair enough, I'll make it u64 in v2.
> 

Well, please do pay attention to any performance impact.  Measurements
with some simple microbenchmark if possible?