linux-kernel - [PATCH] mm/memcg: Skip high limit check in root memcg

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Message-Id: <20230210094550.5125-1-haifeng.xu@shopee.com>
Date:   Fri, 10 Feb 2023 09:45:50 +0000
From:   Haifeng Xu <haifeng.xu@...pee.com>
To:     hannes@...xchg.org
Cc:     mhocko@...nel.org, shakeelb@...gle.com, muchun.song@...ux.dev,
        akpm@...ux-foundation.org, cgroups@...r.kernel.org,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        Haifeng Xu <haifeng.xu@...pee.com>
Subject: [PATCH] mm/memcg: Skip high limit check in root memcg

The high limit checks the memory usage from given memcg to root memcg.
However, there is no limit in root memcg. So this check makes no sense
and we can ignore it.

Signed-off-by: Haifeng Xu <haifeng.xu@...pee.com>
---
 mm/memcontrol.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 73afff8062f9..a31a56598f29 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -2780,6 +2780,10 @@ static int try_charge_memcg(struct mem_cgroup *memcg, gfp_t gfp_mask,
 	do {
 		bool mem_high, swap_high;
 
+		/* There is no need for root memcg to check high limit */
+		if (mem_cgroup_is_root(memcg))
+			break;
+
 		mem_high = page_counter_read(&memcg->memory) >
 			READ_ONCE(memcg->memory.high);
 		swap_high = page_counter_read(&memcg->swap) >
-- 
2.25.1