From: Thomas Gleixner <tglx@linutronix.de>
Date: Wed, 13 Aug 2025 14:57:55 +0000 (+0200)
Subject: memcg: optimize exit to user space
X-Git-Tag: v6.18-rc1~130^2~297
X-Git-Url: http://git.ipfire.org/?a=commitdiff_plain;h=ec45783fce52f358c9e8680d2837bc0d477f16ad;p=thirdparty%2Fkernel%2Fstable.git

memcg: optimize exit to user space

memcg uses TIF_NOTIFY_RESUME to handle reclaiming on exit to user space.
TIF_NOTIFY_RESUME is a multiplexing TIF bit, which is utilized by other
entities as well.

This results in a unconditional mem_cgroup_handle_over_high() call for
every invocation of resume_user_mode_work(), which is a pointless exercise
as most of the time there is no reclaim work to do.

Especially since RSEQ is used by glibc, TIF_NOTIFY_RESUME is raised quite
frequently and the empty calls show up in exit path profiling.

Optimize this by doing a quick check of the reclaim condition before
invoking it.

[akpm@linux-foundation.org: remove now-unneeded test of memcg_nr_pages_over_high==0, per Shakeel]
Link: https://lkml.kernel.org/r/87tt2b6zgs.ffs@tglx
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Roman Gushchin <roman.gushchin@linux.dev>
Acked-by: Johannes Weiner <hannes@cmpxchg.org>
Acked-by: Shakeel Butt <shakeel.butt@linux.dev>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Muchun Song <muchun.song@linux.dev>
Cc: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
index 785173aa0739c..9fa3afc90dd52 100644
--- a/include/linux/memcontrol.h
+++ b/include/linux/memcontrol.h
@@ -900,7 +900,13 @@ unsigned long mem_cgroup_get_zone_lru_size(struct lruvec *lruvec,
 	return READ_ONCE(mz->lru_zone_size[zone_idx][lru]);
 }
 
-void mem_cgroup_handle_over_high(gfp_t gfp_mask);
+void __mem_cgroup_handle_over_high(gfp_t gfp_mask);
+
+static inline void mem_cgroup_handle_over_high(gfp_t gfp_mask)
+{
+	if (unlikely(current->memcg_nr_pages_over_high))
+		__mem_cgroup_handle_over_high(gfp_mask);
+}
 
 unsigned long mem_cgroup_get_max(struct mem_cgroup *memcg);
 
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 8dd7fbed5a942..9712a751690f9 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -2203,7 +2203,7 @@ static unsigned long calculate_high_delay(struct mem_cgroup *memcg,
  * try_charge() (context permitting), as well as from the userland
  * return path where reclaim is always able to block.
  */
-void mem_cgroup_handle_over_high(gfp_t gfp_mask)
+void __mem_cgroup_handle_over_high(gfp_t gfp_mask)
 {
 	unsigned long penalty_jiffies;
 	unsigned long pflags;
@@ -2213,9 +2213,6 @@ void mem_cgroup_handle_over_high(gfp_t gfp_mask)
 	struct mem_cgroup *memcg;
 	bool in_retry = false;
 
-	if (likely(!nr_pages))
-		return;
-
 	memcg = get_mem_cgroup_from_mm(current->mm);
 	current->memcg_nr_pages_over_high = 0;
 
@@ -2486,7 +2483,7 @@ done_restock:
 	if (current->memcg_nr_pages_over_high > MEMCG_CHARGE_BATCH &&
 	    !(current->flags & PF_MEMALLOC) &&
 	    gfpflags_allow_blocking(gfp_mask))
-		mem_cgroup_handle_over_high(gfp_mask);
+		__mem_cgroup_handle_over_high(gfp_mask);
 	return 0;
 }