[PATCH v2] mm: vmscan: abort proactive reclaim early when freezing for suspend

[Richard Chang <richardycc@google.com>]

Proactive reclaim (triggered via memory.reclaim or node sysfs)
checks for pending signals in its outer loop in
user_proactive_reclaim(). However, the inner reclaim
loops—specifically scanning cgroups in shrink_many() and
evicting/aging folios in try_to_shrink_lruvec()—can run for a long
time before returning to the outer loop, especially on systems with
many cgroups or large memory sizes.

During system suspend, the PM freezer attempts to freeze all the tasks
by sending signals. Because the inner loops do not check for pending
signals, the proactive reclaim task can remain stuck in kernel space
for seconds, failing to enter the refrigerator in a timely manner. This
leads to suspend failures due to freeze timeouts, a behavior observed
on Android devices.

This latency issue is specific to proactive reclaim because of its
large, user-defined reclaim targets (could be gigabytes). Since commit
287d5fedb377 ("mm: memcg: use larger batches for proactive reclaim"),
proactive reclaim uses larger decaying batch sizes (starting at 1/4
of the remaining target) to maintain throughput. This keeps the task
in the reclaim loop with a large target for a single syscall
invocation. In contrast, reactive reclaim (global/memcg) has small
targets (SWAP_CLUSTER_MAX, typically 32 pages), allowing to yield or
check signals between attempts quickly.

To fix this, add a signal_pending() check to should_abort_scan() for
proactive reclaim paths. Since should_abort_scan() is called within
the inner scanning and eviction loops, this allows proactive reclaim to
abort early and return to the outer loop, ensuring the task can enter
the refrigerator and allow suspend to proceed.

The check is limited to proactive reclaim (sc->proactive) to avoid
affecting reactive reclaim paths, and wrapped in unlikely() as it
is a slow path.

Signed-off-by: Richard Chang <richardycc@google.com>
---
v2: Update the commit message

 mm/vmscan.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/mm/vmscan.c b/mm/vmscan.c
index 35c3bb15ae96..fb472e924fc7 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -4929,6 +4929,9 @@ static bool should_abort_scan(struct lruvec *lruvec, struct scan_control *sc)
 	int i;
 	enum zone_watermarks mark;
 
+	if (unlikely(sc->proactive && signal_pending(current)))
+		return true;
+
 	if (sc->nr_reclaimed >= max(sc->nr_to_reclaim, compact_gap(sc->order)))
 		return true;
 
-- 
2.55.0.795.g602f6c329a-goog