The patch titled
Subject: mm: kmem: scoped objcg protection
has been added to the -mm mm-unstable branch. Its filename is
mm-kmem-scoped-objcg-protection.patch
This patch will shortly appear at
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-kmem-scoped-objcg-protection.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: scoped objcg protection
Date: Fri, 29 Sep 2023 11:00:54 -0700
Switch to a scope-based protection of the objcg pointer on slab/kmem
allocation paths. Instead of using the get_() semantics in the
pre-allocation hook and put the reference afterwards, let's rely on the
fact that objcg is pinned by the scope.
It's possible because:
1) if the objcg is received from the current task struct, the task is
keeping a reference to the objcg.
2) if the objcg is received from an active memcg (remote charging),
the memcg is pinned by the scope and has a reference to the
corresponding objcg.
Link: https://lkml.kernel.org/r/20230929180056.1122002-5-roman.gushchin@xxxxxxxxx
Signed-off-by: Roman Gushchin (Cruise) <roman.gushchin@xxxxxxxxx>
Cc: David Rientjes <rientjes@xxxxxxxxxx>
Cc: Dennis Zhou <dennis@xxxxxxxxxx>
Cc: Johannes Weiner <hannes@xxxxxxxxxxx>
Cc: Michal Hocko <mhocko@xxxxxxxxxx>
Cc: Muchun Song <muchun.song@xxxxxxxxx>
Cc: Shakeel Butt <shakeelb@xxxxxxxxxx>
Cc: Vlastimil Babka <vbabka@xxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
include/linux/memcontrol.h | 6 ++++
mm/memcontrol.c | 46 +++++++++++++++++++++++++++++++++--
mm/slab.h | 10 ++-----
3 files changed, 53 insertions(+), 9 deletions(-)
--- a/include/linux/memcontrol.h~mm-kmem-scoped-objcg-protection
+++ a/include/linux/memcontrol.h
@@ -1775,6 +1775,12 @@ bool mem_cgroup_kmem_disabled(void);
int __memcg_kmem_charge_page(struct page *page, gfp_t gfp, int order);
void __memcg_kmem_uncharge_page(struct page *page, int order);
+/*
+ * The returned objcg pointer is safe to use without additional
+ * protection within a scope, refer to the implementation for the
+ * additional details.
+ */
+struct obj_cgroup *current_obj_cgroup(void);
struct obj_cgroup *get_obj_cgroup_from_current(void);
struct obj_cgroup *get_obj_cgroup_from_folio(struct folio *folio);
--- a/mm/memcontrol.c~mm-kmem-scoped-objcg-protection
+++ a/mm/memcontrol.c
@@ -3114,6 +3114,48 @@ from_memcg:
return objcg;
}
+__always_inline struct obj_cgroup *current_obj_cgroup(void)
+{
+ struct mem_cgroup *memcg;
+ struct obj_cgroup *objcg;
+
+ if (in_task()) {
+ memcg = current->active_memcg;
+ if (unlikely(memcg))
+ goto from_memcg;
+
+ objcg = READ_ONCE(current->objcg);
+ if (unlikely(current_objcg_needs_update(objcg)))
+ objcg = current_objcg_update(objcg);
+ /*
+ * Objcg reference is kept by the task, so it's safe
+ * to use the objcg by the current task.
+ */
+ return objcg;
+ } else {
+ memcg = this_cpu_read(int_active_memcg);
+ if (unlikely(memcg))
+ goto from_memcg;
+ }
+ return NULL;
+
+from_memcg:
+ for (; !mem_cgroup_is_root(memcg); memcg = parent_mem_cgroup(memcg)) {
+ /*
+ * Memcg pointer is protected by scope (see set_active_memcg())
+ * and is pinning the corresponding objcg, so objcg can't go
+ * away and can be used within the scope without any additional
+ * protection.
+ */
+ objcg = rcu_dereference_check(memcg->objcg, 1);
+ if (likely(objcg))
+ break;
+ objcg = NULL;
+ }
+
+ return objcg;
+}
+
struct obj_cgroup *get_obj_cgroup_from_folio(struct folio *folio)
{
struct obj_cgroup *objcg;
@@ -3208,15 +3250,15 @@ int __memcg_kmem_charge_page(struct page
struct obj_cgroup *objcg;
int ret = 0;
- objcg = get_obj_cgroup_from_current();
+ objcg = current_obj_cgroup();
if (objcg) {
ret = obj_cgroup_charge_pages(objcg, gfp, 1 << order);
if (!ret) {
+ obj_cgroup_get(objcg);
page->memcg_data = (unsigned long)objcg |
MEMCG_DATA_KMEM;
return 0;
}
- obj_cgroup_put(objcg);
}
return ret;
}
--- a/mm/slab.h~mm-kmem-scoped-objcg-protection
+++ a/mm/slab.h
@@ -484,7 +484,7 @@ static inline bool memcg_slab_pre_alloc_
if (!(flags & __GFP_ACCOUNT) && !(s->flags & SLAB_ACCOUNT))
return true;
- objcg = get_obj_cgroup_from_current();
+ objcg = current_obj_cgroup();
if (!objcg)
return true;
@@ -497,17 +497,14 @@ static inline bool memcg_slab_pre_alloc_
css_put(&memcg->css);
if (ret)
- goto out;
+ return false;
}
if (obj_cgroup_charge(objcg, flags, objects * obj_full_size(s)))
- goto out;
+ return false;
*objcgp = objcg;
return true;
-out:
- obj_cgroup_put(objcg);
- return false;
}
static inline void memcg_slab_post_alloc_hook(struct kmem_cache *s,
@@ -542,7 +539,6 @@ static inline void memcg_slab_post_alloc
obj_cgroup_uncharge(objcg, obj_full_size(s));
}
}
- obj_cgroup_put(objcg);
}
static inline void memcg_slab_free_hook(struct kmem_cache *s, struct slab *slab,
_
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
