+ mm-memcontrol-prevent-starvation-when-writing-memoryhigh.patch added to -mm tree

+ mm-memcontrol-prevent-starvation-when-writing-memoryhigh.patch added to -mm tree

[akpm]

The patch titled
     Subject: mm: memcontrol: prevent starvation when writing memory.high
has been added to the -mm tree.  Its filename is
     mm-memcontrol-prevent-starvation-when-writing-memoryhigh.patch

This patch should soon appear at
    https://ozlabs.org/~akpm/mmots/broken-out/mm-memcontrol-prevent-starvation-when-writing-memoryhigh.patch
and later at
    https://ozlabs.org/~akpm/mmotm/broken-out/mm-memcontrol-prevent-starvation-when-writing-memoryhigh.patch

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------------------------------------------------------
From: Johannes Weiner <hannes@cmpxchg.org>
Subject: mm: memcontrol: prevent starvation when writing memory.high

When a value is written to a cgroup's memory.high control file, the
write() context first tries to reclaim the cgroup to size before putting
the limit in place for the workload.  Concurrent charges from the workload
can keep such a write() looping in reclaim indefinitely.

In the past, a write to memory.high would first put the limit in place for
the workload, then do targeted reclaim until the new limit has been met -
similar to how we do it for memory.max.  This wasn't prone to the
described starvation issue.  However, this sequence could cause excessive
latencies in the workload, when allocating threads could be put into long
penalty sleeps on the sudden memory.high overage created by the write(),
before that had a chance to work it off.

Now that memory_high_write() performs reclaim before enforcing the new
limit, reflect that the cgroup may well fail to converge due to concurrent
workload activity.  Bail out of the loop after a few tries.

Link: https://lkml.kernel.org/r/20210112163011.127833-1-hannes@cmpxchg.org
Fixes: 536d3bf261a2 ("mm: memcontrol: avoid workload stalls when lowering memory.high")
Signed-off-by: Johannes Weiner <hannes@cmpxchg.org>
Reviewed-by: Shakeel Butt <shakeelb@google.com>
Reported-by: Tejun Heo <tj@kernel.org>
Cc: Roman Gushchin <guro@fb.com>
Cc: Michal Hocko <mhocko@suse.com>
Cc: <stable@vger.kernel.org>	[5.8+]
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 mm/memcontrol.c |    7 +++----
 1 file changed, 3 insertions(+), 4 deletions(-)

--- a/mm/memcontrol.c~mm-memcontrol-prevent-starvation-when-writing-memoryhigh
+++ a/mm/memcontrol.c
@@ -6273,7 +6273,6 @@ static ssize_t memory_high_write(struct
 
 	for (;;) {
 		unsigned long nr_pages = page_counter_read(&memcg->memory);
-		unsigned long reclaimed;
 
 		if (nr_pages <= high)
 			break;
@@ -6287,10 +6286,10 @@ static ssize_t memory_high_write(struct
 			continue;
 		}
 
-		reclaimed = try_to_free_mem_cgroup_pages(memcg, nr_pages - high,
-							 GFP_KERNEL, true);
+		try_to_free_mem_cgroup_pages(memcg, nr_pages - high,
+					     GFP_KERNEL, true);
 
-		if (!reclaimed && !nr_retries--)
+		if (!nr_retries--)
 			break;
 	}
 
_

Patches currently in -mm which might be from hannes@cmpxchg.org are

mm-memcontrol-prevent-starvation-when-writing-memoryhigh.patch