The patch titled
Subject: mm: kmem: optimize get_obj_cgroup_from_current()
has been added to the -mm mm-unstable branch. Its filename is
mm-kmem-optimize-get_obj_cgroup_from_current.patch
This patch will shortly appear at
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-kmem-optimize-get_obj_cgroup_from_current.patch
This patch will later appear in the mm-unstable branch at
git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
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------------------------------------------------------
From: Roman Gushchin <roman.gushchin@xxxxxxxxx>
Subject: mm: kmem: optimize get_obj_cgroup_from_current()
Date: Mon, 9 Oct 2023 17:09:25 -0700
Patch series "mm: improve performance of accounted kernel memory
allocations", v2.
This patchset improves the performance of accounted kernel memory
allocations by ~30% as measured by a micro-benchmark [1]. The benchmark
is very straightforward: 1M of 64 bytes-large kmalloc() allocations.
Below are results with the disabled kernel memory accounting, the original state
and with this patchset applied.
| | Kmem disabled | Original | Patched | Delta |
|-------------+---------------+----------+---------+--------|
| User cgroup | 29764 | 84548 | 59078 | -30.0% |
| Root cgroup | 29742 | 48342 | 31501 | -34.8% |
As we can see, the patchset removes the majority of the overhead when
there is no actual accounting (a task belongs to the root memory cgroup)
and almost halves the accounting overhead otherwise.
The main idea is to get rid of unnecessary memcg to objcg conversions and
switch to a scope-based protection of objcgs, which eliminates extra
operations with objcg reference counters under a rcu read lock. More
details are provided in individual commit descriptions.
This patch (of 5):
Manually inline memcg_kmem_bypass() and active_memcg() to speed up
get_obj_cgroup_from_current() by avoiding duplicate in_task() checks and
active_memcg() readings.
Also add a likely() macro to __get_obj_cgroup_from_memcg():
obj_cgroup_tryget() should succeed at almost all times except a very
unlikely race with the memcg deletion path.
Link: https://lkml.kernel.org/r/20231010000929.450702-1-roman.gushchin@xxxxxxxxx
Link: https://lkml.kernel.org/r/20231010000929.450702-2-roman.gushchin@xxxxxxxxx
Signed-off-by: Roman Gushchin (Cruise) <roman.gushchin@xxxxxxxxx>
Acked-by: Shakeel Butt <shakeelb@xxxxxxxxxx>
Acked-by: Johannes Weiner <hannes@xxxxxxxxxxx>
Cc: David Rientjes <rientjes@xxxxxxxxxx>
Cc: Dennis Zhou <dennis@xxxxxxxxxx>
Cc: Michal Hocko <mhocko@xxxxxxxxxx>
Cc: Muchun Song <muchun.song@xxxxxxxxx>
Cc: Naresh Kamboju <naresh.kamboju@xxxxxxxxxx>
Cc: Vlastimil Babka <vbabka@xxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/memcontrol.c | 34 ++++++++++++++--------------------
1 file changed, 14 insertions(+), 20 deletions(-)
--- a/mm/memcontrol.c~mm-kmem-optimize-get_obj_cgroup_from_current
+++ a/mm/memcontrol.c
@@ -1110,19 +1110,6 @@ struct mem_cgroup *get_mem_cgroup_from_m
}
EXPORT_SYMBOL(get_mem_cgroup_from_mm);
-static __always_inline bool memcg_kmem_bypass(void)
-{
- /* Allow remote memcg charging from any context. */
- if (unlikely(active_memcg()))
- return false;
-
- /* Memcg to charge can't be determined. */
- if (!in_task() || !current->mm || (current->flags & PF_KTHREAD))
- return true;
-
- return false;
-}
-
/**
* get_mem_cgroup_from_current - Obtain a reference on current task's memcg.
*/
@@ -3113,7 +3100,7 @@ static struct obj_cgroup *__get_obj_cgro
for (; !mem_cgroup_is_root(memcg); memcg = parent_mem_cgroup(memcg)) {
objcg = rcu_dereference(memcg->objcg);
- if (objcg && obj_cgroup_tryget(objcg))
+ if (likely(objcg && obj_cgroup_tryget(objcg)))
break;
objcg = NULL;
}
@@ -3122,16 +3109,23 @@ static struct obj_cgroup *__get_obj_cgro
__always_inline struct obj_cgroup *get_obj_cgroup_from_current(void)
{
- struct obj_cgroup *objcg = NULL;
struct mem_cgroup *memcg;
+ struct obj_cgroup *objcg;
- if (memcg_kmem_bypass())
- return NULL;
+ if (in_task()) {
+ memcg = current->active_memcg;
+
+ /* Memcg to charge can't be determined. */
+ if (likely(!memcg) && (!current->mm || (current->flags & PF_KTHREAD)))
+ return NULL;
+ } else {
+ memcg = this_cpu_read(int_active_memcg);
+ if (likely(!memcg))
+ return NULL;
+ }
rcu_read_lock();
- if (unlikely(active_memcg()))
- memcg = active_memcg();
- else
+ if (!memcg)
memcg = mem_cgroup_from_task(current);
objcg = __get_obj_cgroup_from_memcg(memcg);
rcu_read_unlock();
_
Patches currently in -mm which might be from roman.gushchin@xxxxxxxxx are
mm-kmem-optimize-get_obj_cgroup_from_current.patch
mm-kmem-add-direct-objcg-pointer-to-task_struct.patch
mm-kmem-make-memcg-keep-a-reference-to-the-original-objcg.patch
mm-kmem-scoped-objcg-protection.patch
percpu-scoped-objcg-protection.patch
