mm: vmscan: abort proactive reclaim early when freezing for suspend

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 tasks by
sending fake signals (setting TIF_SIGPENDING).  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
inner reclaim loop for extended periods.  In contrast, reactive reclaim
(global/memcg) uses small targets (SWAP_CLUSTER_MAX, typically 32 pages),
allowing it to return to the outer loop and check signals frequently.

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 in user_proactive_reclaim().

Additionally, return -ERESTARTSYS instead of -EINTR in
user_proactive_reclaim().  When interrupted by system suspend, returning
-ERESTARTSYS allows the task to enter the refrigerator and automatically
restart the syscall upon resume, making the freezer transparent to
userspace.  For real signals, the signal layer will either restart the
syscall (if SA_RESTART is set) or return -EINTR to userspace.

This fix specifically targets Multi-Gen LRU (MGLRU).  Classic LRU's scan
targets per iteration are strictly bounded by get_scan_count(), which
ensures it returns to the outer loop more frequently.

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

Link: https://lore.kernel.org/20260720044103.905191-1-richardycc@google.com
Fixes: 287d5fedb377 ("mm: memcg: use larger batches for proactive reclaim")
Fixes: 94968384dde1 ("memcg: introduce per-memcg reclaim interface")
Suggested-by: Michal Hocko <mhocko@suse.com>
Suggested-by: Oleg Nesterov <oleg@redhat.com>
Signed-off-by: Richard Chang <richardycc@google.com>
Acked-by: Michal Hocko <mhocko@suse.com>
Cc: Axel Rasmussen <axelrasmussen@google.com>
Cc: Barry Song <baohua@kernel.org>
Cc: David Hildenbrand <david@kernel.org>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Kairui Song <kasong@tencent.com>
Cc: Lorenzo Stoakes <ljs@kernel.org>
Cc: Martin Liu <liumartin@google.com>
Cc: Minchan Kim <minchan@kernel.org>
Cc: Shakeel Butt <shakeel.butt@linux.dev>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: T.J. Mercier <tjmercier@google.com>
Cc: Wei Xu <weixugc@google.com>
Cc: Yuanchu Xie <yuanchu@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/mm/vmscan.c b/mm/vmscan.c
index 1a142c58700d00de7a443792a5e3457f5f0cb56c..56708d1d2dfd54ff6c9cb713b93dfecb9f5476e2 100644 (file)
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -4926,6 +4926,9 @@ 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;
 
@@ -7906,8 +7909,15 @@ int user_proactive_reclaim(char *buf,
                unsigned long batch_size = (nr_to_reclaim - nr_reclaimed) / 4;
                unsigned long reclaimed;
 
+               /*
+                * Return -ERESTARTSYS to allow the freezer to interrupt the
+                * task. The syscall will be transparently restarted upon
+                * resume. For real signals, it either restarts the syscall
+                * (if SA_RESTART is set) or is converted to -EINTR by the
+                * signal layer.
+                */
                if (signal_pending(current))
-                       return -EINTR;
+                       return -ERESTARTSYS;
 
                /*
                 * This is the final attempt, drain percpu lru caches in the