linux-kernel - Re: [PATCH v3] memcg: introduce non-blocking limit setting option

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Message-Id: <20250506175316.1ca96d3aab2a28086fffa33a@linux-foundation.org>
Date: Tue, 6 May 2025 17:53:16 -0700
From: Andrew Morton <akpm@...ux-foundation.org>
To: Shakeel Butt <shakeel.butt@...ux.dev>
Cc: Johannes Weiner <hannes@...xchg.org>, Michal Hocko <mhocko@...nel.org>,
 Roman Gushchin <roman.gushchin@...ux.dev>, Muchun Song
 <muchun.song@...ux.dev>, linux-mm@...ck.org, cgroups@...r.kernel.org,
 linux-kernel@...r.kernel.org, Meta kernel team <kernel-team@...a.com>, Greg
 Thelen <gthelen@...gle.com>, Michal Koutný
 <mkoutny@...e.com>, Tejun Heo <tj@...nel.org>, Yosry Ahmed
 <yosry.ahmed@...ux.dev>, Christian Brauner <brauner@...nel.org>
Subject: Re: [PATCH v3] memcg: introduce non-blocking limit setting option

Thanks, I queued this as a -fix:


--- a/Documentation/admin-guide/cgroup-v2.rst~memcg-introduce-non-blocking-limit-setting-option-v3
+++ a/Documentation/admin-guide/cgroup-v2.rst
@@ -1299,12 +1299,17 @@ PAGE_SIZE multiple when read back.
 	monitors the limited cgroup to alleviate heavy reclaim
 	pressure.
 
-        If memory.high is opened with O_NONBLOCK then the synchronous
-        reclaim is bypassed. This is useful for admin processes that
-        need to dynamically adjust the job's memory limits without
-        expending their own CPU resources on memory reclamation. The
-        job will trigger the reclaim and/or get throttled on its
-        next charge request.
+	If memory.high is opened with O_NONBLOCK then the synchronous
+	reclaim is bypassed. This is useful for admin processes that
+	need to dynamically adjust the job's memory limits without
+	expending their own CPU resources on memory reclamation. The
+	job will trigger the reclaim and/or get throttled on its
+	next charge request.
+
+	Please note that with O_NONBLOCK, there is a chance that the
+	target memory cgroup may take indefinite amount of time to
+	reduce usage below the limit due to delayed charge request or
+	busy-hitting its memory to slow down reclaim.
 
   memory.max
 	A read-write single value file which exists on non-root
@@ -1323,12 +1328,17 @@ PAGE_SIZE multiple when read back.
 	Caller could retry them differently, return into userspace
 	as -ENOMEM or silently ignore in cases like disk readahead.
 
-        If memory.max is opened with O_NONBLOCK, then the synchronous
-        reclaim and oom-kill are bypassed. This is useful for admin
-        processes that need to dynamically adjust the job's memory limits
-        without expending their own CPU resources on memory reclamation.
-        The job will trigger the reclaim and/or oom-kill on its next
-        charge request.
+	If memory.max is opened with O_NONBLOCK, then the synchronous
+	reclaim and oom-kill are bypassed. This is useful for admin
+	processes that need to dynamically adjust the job's memory limits
+	without expending their own CPU resources on memory reclamation.
+	The job will trigger the reclaim and/or oom-kill on its next
+	charge request.
+
+	Please note that with O_NONBLOCK, there is a chance that the
+	target memory cgroup may take indefinite amount of time to
+	reduce usage below the limit due to delayed charge request or
+	busy-hitting its memory to slow down reclaim.
 
   memory.reclaim
 	A write-only nested-keyed file which exists for all cgroups.
_