netdev - Re: [PATCH net-next] net-memcg: pass in gfp_t mask to mem_cgroup_charge

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Date:   Wed, 12 Oct 2022 20:16:50 -0700
From:   Jakub Kicinski <kuba@...nel.org>
To:     Shakeel Butt <shakeelb@...gle.com>
Cc:     Wei Wang <weiwan@...gle.com>, Eric Dumazet <edumazet@...gle.com>,
        netdev@...r.kernel.org, "David S . Miller" <davem@...emloft.net>,
        cgroups@...r.kernel.org, linux-mm@...ck.org,
        Roman Gushchin <roman.gushchin@...ux.dev>
Subject: Re: [PATCH net-next] net-memcg: pass in gfp_t mask to
 mem_cgroup_charge_skmem()

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;
 }

The problem normally reproes reliably within 10min -- 30min and counting
and the application-level latency has not spiked.