linux-kernel - [PATCH] memcg: Optimize exit to user space

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [thread-next>] [day] [month] [year] [list]

Message-ID: <87tt2b6zgs.ffs@tglx>
Date: Wed, 13 Aug 2025 16:57:55 +0200
From: Thomas Gleixner <tglx@...utronix.de>
To: linux-mm@...ck.org
Cc: LKML <linux-kernel@...r.kernel.org>, Peter Zijlstra
 <peterz@...radead.org>, Johannes Weiner <hannes@...xchg.org>, Michal Hocko
 <mhocko@...nel.org>, Roman Gushchin <roman.gushchin@...ux.dev>, Shakeel
 Butt <shakeel.butt@...ux.dev>, Muchun Song <muchun.song@...ux.dev>,
 cgroups@...r.kernel.org, Andrew Morton <akpm@...ux-foundation.org>
Subject: [PATCH] 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.

Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
Cc: Johannes Weiner <hannes@...xchg.org>
Cc: Michal Hocko <mhocko@...nel.org>
Cc: Roman Gushchin <roman.gushchin@...ux.dev>
Cc: Shakeel Butt <shakeel.butt@...ux.dev>
Cc: Muchun Song <muchun.song@...ux.dev>
Cc: Andrew Morton <akpm@...ux-foundation.org>
---
 include/linux/memcontrol.h |    8 +++++++-
 mm/memcontrol.c            |    4 ++--
 2 files changed, 9 insertions(+), 3 deletions(-)

--- a/include/linux/memcontrol.h
+++ b/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
+++ b/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 @@ static int try_charge_memcg(struct mem_c
 	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;
 }