+ memcg-optimize-exit-to-user-space.patch added to mm-new branch

[Andrew Morton <akpm@linux-foundation.org>]

The patch titled
     Subject: memcg: optimize exit to user space
has been added to the -mm mm-new branch.  Its filename is
     memcg-optimize-exit-to-user-space.patch

This patch will shortly appear at
     https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/memcg-optimize-exit-to-user-space.patch

This patch will later appear in the mm-new branch at
    git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

Note, mm-new is a provisional staging ground for work-in-progress
patches, and acceptance into mm-new is a notification for others take
notice and to finish up reviews.  Please do not hesitate to respond to
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------------------------------------------------------
From: Thomas Gleixner <tglx@linutronix.de>
Subject: memcg: optimize exit to user space
Date: Wed, 13 Aug 2025 16:57:55 +0200

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.

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>
---

 include/linux/memcontrol.h |    8 +++++++-
 mm/memcontrol.c            |    4 ++--
 2 files changed, 9 insertions(+), 3 deletions(-)

--- a/include/linux/memcontrol.h~memcg-optimize-exit-to-user-space
+++ a/include/linux/memcontrol.h
@@ -900,7 +900,13 @@ unsigned long mem_cgroup_get_zone_lru_si
 	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);
 
--- a/mm/memcontrol.c~memcg-optimize-exit-to-user-space
+++ a/mm/memcontrol.c
@@ -2203,7 +2203,7 @@ static unsigned long calculate_high_dela
  * 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;
@@ -2486,7 +2486,7 @@ 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;
 }
 
_

Patches currently in -mm which might be from tglx@linutronix.de are

memcg-optimize-exit-to-user-space.patch