linux-kernel - [PATCH] mm: allow exiting processes to exceed the memory.max limit

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Message-ID: <20241209124233.3543f237@fangorn>
Date: Mon, 9 Dec 2024 12:42:33 -0500
From: Rik van Riel <riel@...riel.com>
To: Johannes Weiner <hannes@...xchg.org>
Cc: kernel-team@...a.com, linux-kernel@...r.kernel.org, linux-mm@...ck.org,
 Michal Hocko <mhocko@...nel.org>, Roman Gushchin
 <roman.gushchin@...ux.dev>, Shakeel Butt <shakeel.butt@...ux.dev>, Muchun
 Song <muchun.song@...ux.dev>, Andrew Morton <akpm@...ux-foundation.org>,
 cgroups@...r.kernel.org
Subject: [PATCH] mm: allow exiting processes to exceed the memory.max limit

It is possible for programs to get stuck in exit, when their
memcg is at or above the memory.max limit, and things like
the do_futex() call from mm_release() need to page memory in.

This can hang forever, but it really doesn't have to.

The amount of memory that the exit path will page into memory
should be relatively small, and letting exit proceed faster
will free up memory faster.

Allow PF_EXITING tasks to bypass the cgroup memory.max limit
the same way PF_MEMALLOC already does.

Signed-off-by: Rik van Riel <riel@...riel.com>
---
 mm/memcontrol.c | 9 +++++----
 1 file changed, 5 insertions(+), 4 deletions(-)

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 7b3503d12aaf..d1abef1138ff 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -2218,11 +2218,12 @@ int try_charge_memcg(struct mem_cgroup *memcg, gfp_t gfp_mask,
 
 	/*
 	 * Prevent unbounded recursion when reclaim operations need to
-	 * allocate memory. This might exceed the limits temporarily,
-	 * but we prefer facilitating memory reclaim and getting back
-	 * under the limit over triggering OOM kills in these cases.
+	 * allocate memory, or the process is exiting. This might exceed
+	 * the limits temporarily, but we prefer facilitating memory reclaim
+	 * and getting back under the limit over triggering OOM kills in
+	 * these cases.
 	 */
-	if (unlikely(current->flags & PF_MEMALLOC))
+	if (unlikely(current->flags & (PF_MEMALLOC | PF_EXITING)))
 		goto force;
 
 	if (unlikely(task_in_memcg_oom(current)))
-- 
2.47.0