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

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

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?