Re: [PATCH net-next 1/2] net: Keep sk->sk_forward_alloc as a proper size

Shakeel Butt
2023-05-11T21:18:49Z

On Thu, May 11, 2023 at 09:26:46AM +0000, Zhang, Cathy wrote:
>
[...]
>
> 8.98% mc-worker [kernel.vmlinux] [k] page_counter_cancel
> |
> --8.97%--page_counter_cancel
> |
> --8.97%--page_counter_uncharge
> drain_stock
> __refill_stock
> refill_stock
> |
> --8.91%--try_charge_memcg
> mem_cgroup_charge_skmem

I do want to understand for above which specific condition in
__refill_stock is causing to drain stock in the charge code path. Can
you please re-run and profile your test with following code snippet (or
use any other mechanism which can answer the question)?

From f1d91043f21f4b29717c78615b374d79fc021d1f Mon Sep 17 00:00:00 2001
From: Shakeel Butt <shakeelb@google.com>
Date: Thu, 11 May 2023 20:00:19 +0000
Subject: [PATCH] Debug drain on charging.

---
mm/memcontrol.c | 14 ++++++++++++--
1 file changed, 12 insertions(+), 2 deletions(-)

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index d31fb1e2cb33..4c1c3d90a4a3 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -2311,6 +2311,16 @@ static void drain_local_stock(struct work_struct *dummy)
obj_cgroup_put(old);
}

+static noinline void drain_stock_1(struct memcg_stock_pcp *stock)
+{
+ drain_stock(stock);
+}
+
+static noinline void drain_stock_2(struct memcg_stock_pcp *stock)
+{
+ drain_stock(stock);
+}
+
/*
* Cache charges(val) to local per_cpu area.
* This will be consumed by consume_stock() function, later.
@@ -2321,14 +2331,14 @@ static void __refill_stock(struct mem_cgroup *memcg, unsigned int nr_pages)

stock = this_cpu_ptr(&memcg_stock);
if (READ_ONCE(stock->cached) != memcg) { /* reset if necessary */
- drain_stock(stock);
+ drain_stock_1(stock);
css_get(&memcg->css);
WRITE_ONCE(stock->cached, memcg);
}
stock->nr_pages += nr_pages;

if (stock->nr_pages > MEMCG_CHARGE_BATCH)
- drain_stock(stock);
+ drain_stock_2(stock);
}

static void refill_stock(struct mem_cgroup *memcg, unsigned int nr_pages)
--
2.40.1.606.ga4b1b128d6-goog