On Wed, Oct 12, 2022 at 8:16 PM Jakub Kicinski <kuba@xxxxxxxxxx> wrote:
>
> On Wed, 12 Oct 2022 18:40:50 -0700 Jakub Kicinski wrote:
> > Did the fact that we used to force charge not potentially cause
> > reclaim, tho? Letting TCP accept the next packet even if it had
> > to drop the current one?
>
> I pushed this little nugget to one affected machine via KLP:
>
> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> index 03ffbb255e60..c1ca369a1b77 100644
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -7121,6 +7121,10 @@ bool mem_cgroup_charge_skmem(struct mem_cgroup *memcg, unsigned int nr_pages,
> return true;
> }
>
> + if (gfp_mask == GFP_NOWAIT) {
> + try_charge(memcg, gfp_mask|__GFP_NOFAIL, nr_pages);
> + refill_stock(memcg, nr_pages);
> + }
> return false;
> }
>
AFAICT, if you force charge by passing __GFP_NOFAIL to try_charge(),
you should return true to tell the caller that the nr_pages is
actually being charged. Although I am not very sure what
refill_stock() does. Does that "uncharge" those pages?
> The problem normally reproes reliably within 10min -- 30min and counting
> and the application-level latency has not spiked.
