linux-kernel - [PATCH] mm: memcontrol: restore proper dirty throttling when memory.high changes

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Message-Id: <20200728135210.379885-1-hannes@cmpxchg.org>
Date:   Tue, 28 Jul 2020 09:52:09 -0400
From:   Johannes Weiner <hannes@...xchg.org>
To:     Andrew Morton <akpm@...ux-foundation.org>
Cc:     Michal Hocko <mhocko@...e.com>, Roman Gushchin <guro@...com>,
        linux-mm@...ck.org, cgroups@...r.kernel.org,
        linux-kernel@...r.kernel.org, kernel-team@...com
Subject: [PATCH] mm: memcontrol: restore proper dirty throttling when memory.high changes

Commit 8c8c383c04f6 ("mm: memcontrol: try harder to set a new
memory.high") inadvertently removed a callback to recalculate the
writeback cache size in light of a newly configured memory.high limit.

Without letting the writeback cache know about a potentially heavily
reduced limit, it may permit too many dirty pages, which can cause
unnecessary reclaim latencies or even avoidable OOM situations.

This was spotted while reading the code, it hasn't knowingly caused
any problems in practice so far.

Fixes: 8c8c383c04f6 ("mm: memcontrol: try harder to set a new memory.high")
Signed-off-by: Johannes Weiner <hannes@...xchg.org>
---
 mm/memcontrol.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 13f559af1ab6..805a44bf948c 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -6071,6 +6071,7 @@ static ssize_t memory_high_write(struct kernfs_open_file *of,
 			break;
 	}

+	memcg_wb_domain_size_changed(memcg);
 	return nbytes;
 }

-- 
2.27.0