The patch titled
Subject: mm: memcg/slab: stop setting page->mem_cgroup pointer for slab pages
has been added to the -mm tree. Its filename is
mm-stop-setting-page-mem_cgroup-pointer-for-slab-pages.patch
This patch should soon appear at
http://ozlabs.org/~akpm/mmots/broken-out/mm-stop-setting-page-mem_cgroup-pointer-for-slab-pages.patch
and later at
http://ozlabs.org/~akpm/mmotm/broken-out/mm-stop-setting-page-mem_cgroup-pointer-for-slab-pages.patch
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------------------------------------------------------
From: Roman Gushchin <guro@xxxxxx>
Subject: mm: memcg/slab: stop setting page->mem_cgroup pointer for slab pages
Every slab page charged to a non-root memory cgroup has a pointer to the
memory cgroup and holds a reference to it, which protects a non-empty
memory cgroup from being released. At the same time the page has a
pointer to the corresponding kmem_cache, and also hold a reference to the
kmem_cache. And kmem_cache by itself holds a reference to the cgroup.
So there is clearly some redundancy, which allows to stop setting the
page->mem_cgroup pointer and rely on getting memcg pointer indirectly via
kmem_cache. Further it will allow to change this pointer easier, without
a need to go over all charged pages.
So let's stop setting page->mem_cgroup pointer for slab pages, and stop
using the css refcounter directly for protecting the memory cgroup from
going away. Instead rely on kmem_cache as an intermediate object.
Make sure that vmstats and shrinker lists are working as previously, as
well as /proc/kpagecgroup interface.
Link: http://lkml.kernel.org/r/20190611231813.3148843-10-guro@xxxxxx
Signed-off-by: Roman Gushchin <guro@xxxxxx>
Acked-by: Vladimir Davydov <vdavydov.dev@xxxxxxxxx>
Cc: Christoph Lameter <cl@xxxxxxxxx>
Cc: Johannes Weiner <hannes@xxxxxxxxxxx>
Cc: Michal Hocko <mhocko@xxxxxxxx>
Cc: Shakeel Butt <shakeelb@xxxxxxxxxx>
Cc: Waiman Long <longman@xxxxxxxxxx>
Cc: David Rientjes <rientjes@xxxxxxxxxx>
Cc: Joonsoo Kim <iamjoonsoo.kim@xxxxxxx>
Cc: Pekka Enberg <penberg@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/list_lru.c | 3 +
mm/memcontrol.c | 12 ++++---
mm/slab.h | 74 +++++++++++++++++++++++++++++++++++++---------
3 files changed, 70 insertions(+), 19 deletions(-)
--- a/mm/list_lru.c~mm-stop-setting-page-mem_cgroup-pointer-for-slab-pages
+++ a/mm/list_lru.c
@@ -12,6 +12,7 @@
#include <linux/slab.h>
#include <linux/mutex.h>
#include <linux/memcontrol.h>
+#include "slab.h"
#ifdef CONFIG_MEMCG_KMEM
static LIST_HEAD(list_lrus);
@@ -63,7 +64,7 @@ static __always_inline struct mem_cgroup
if (!memcg_kmem_enabled())
return NULL;
page = virt_to_head_page(ptr);
- return page->mem_cgroup;
+ return memcg_from_slab_page(page);
}
static inline struct list_lru_one *
--- a/mm/memcontrol.c~mm-stop-setting-page-mem_cgroup-pointer-for-slab-pages
+++ a/mm/memcontrol.c
@@ -486,7 +486,10 @@ ino_t page_cgroup_ino(struct page *page)
unsigned long ino = 0;
rcu_read_lock();
- memcg = READ_ONCE(page->mem_cgroup);
+ if (PageHead(page) && PageSlab(page))
+ memcg = memcg_from_slab_page(page);
+ else
+ memcg = READ_ONCE(page->mem_cgroup);
while (memcg && !(memcg->css.flags & CSS_ONLINE))
memcg = parent_mem_cgroup(memcg);
if (memcg)
@@ -2802,9 +2805,6 @@ int __memcg_kmem_charge_memcg(struct pag
cancel_charge(memcg, nr_pages);
return -ENOMEM;
}
-
- page->mem_cgroup = memcg;
-
return 0;
}
@@ -2827,8 +2827,10 @@ int __memcg_kmem_charge(struct page *pag
memcg = get_mem_cgroup_from_current();
if (!mem_cgroup_is_root(memcg)) {
ret = __memcg_kmem_charge_memcg(page, gfp, order, memcg);
- if (!ret)
+ if (!ret) {
+ page->mem_cgroup = memcg;
__SetPageKmemcg(page);
+ }
}
css_put(&memcg->css);
return ret;
--- a/mm/slab.h~mm-stop-setting-page-mem_cgroup-pointer-for-slab-pages
+++ a/mm/slab.h
@@ -255,30 +255,67 @@ static inline struct kmem_cache *memcg_r
return s->memcg_params.root_cache;
}
+/*
+ * Expects a pointer to a slab page. Please note, that PageSlab() check
+ * isn't sufficient, as it returns true also for tail compound slab pages,
+ * which do not have slab_cache pointer set.
+ * So this function assumes that the page can pass PageHead() and PageSlab()
+ * checks.
+ */
+static inline struct mem_cgroup *memcg_from_slab_page(struct page *page)
+{
+ struct kmem_cache *s;
+
+ s = READ_ONCE(page->slab_cache);
+ if (s && !is_root_cache(s))
+ return s->memcg_params.memcg;
+
+ return NULL;
+}
+
+/*
+ * Charge the slab page belonging to the non-root kmem_cache.
+ * Can be called for non-root kmem_caches only.
+ */
static __always_inline int memcg_charge_slab(struct page *page,
gfp_t gfp, int order,
struct kmem_cache *s)
{
+ struct mem_cgroup *memcg;
+ struct lruvec *lruvec;
int ret;
- if (is_root_cache(s))
- return 0;
-
- ret = memcg_kmem_charge_memcg(page, gfp, order, s->memcg_params.memcg);
+ memcg = s->memcg_params.memcg;
+ ret = memcg_kmem_charge_memcg(page, gfp, order, memcg);
if (ret)
return ret;
+ lruvec = mem_cgroup_lruvec(page_pgdat(page), memcg);
+ mod_lruvec_state(lruvec, cache_vmstat_idx(s), 1 << order);
+
+ /* transer try_charge() page references to kmem_cache */
percpu_ref_get_many(&s->memcg_params.refcnt, 1 << order);
+ css_put_many(&memcg->css, 1 << order);
return 0;
}
+/*
+ * Uncharge a slab page belonging to a non-root kmem_cache.
+ * Can be called for non-root kmem_caches only.
+ */
static __always_inline void memcg_uncharge_slab(struct page *page, int order,
struct kmem_cache *s)
{
- if (!is_root_cache(s))
- percpu_ref_put_many(&s->memcg_params.refcnt, 1 << order);
- memcg_kmem_uncharge(page, order);
+ struct mem_cgroup *memcg;
+ struct lruvec *lruvec;
+
+ memcg = s->memcg_params.memcg;
+ lruvec = mem_cgroup_lruvec(page_pgdat(page), memcg);
+ mod_lruvec_state(lruvec, cache_vmstat_idx(s), -(1 << order));
+ memcg_kmem_uncharge_memcg(page, order, memcg);
+
+ percpu_ref_put_many(&s->memcg_params.refcnt, 1 << order);
}
extern void slab_init_memcg_params(struct kmem_cache *);
@@ -314,6 +351,11 @@ static inline struct kmem_cache *memcg_r
return s;
}
+static inline struct mem_cgroup *memcg_from_slab_page(struct page *page)
+{
+ return NULL;
+}
+
static inline int memcg_charge_slab(struct page *page, gfp_t gfp, int order,
struct kmem_cache *s)
{
@@ -351,18 +393,24 @@ static __always_inline int charge_slab_p
gfp_t gfp, int order,
struct kmem_cache *s)
{
- int ret = memcg_charge_slab(page, gfp, order, s);
-
- if (!ret)
- mod_lruvec_page_state(page, cache_vmstat_idx(s), 1 << order);
+ if (is_root_cache(s)) {
+ mod_node_page_state(page_pgdat(page), cache_vmstat_idx(s),
+ 1 << order);
+ return 0;
+ }
- return ret;
+ return memcg_charge_slab(page, gfp, order, s);
}
static __always_inline void uncharge_slab_page(struct page *page, int order,
struct kmem_cache *s)
{
- mod_lruvec_page_state(page, cache_vmstat_idx(s), -(1 << order));
+ if (is_root_cache(s)) {
+ mod_node_page_state(page_pgdat(page), cache_vmstat_idx(s),
+ -(1 << order));
+ return;
+ }
+
memcg_uncharge_slab(page, order, s);
}
_
Patches currently in -mm which might be from guro@xxxxxx are
mm-postpone-kmem_cache-memcg-pointer-initialization-to-memcg_link_cache.patch
mm-rename-slab-delayed-deactivation-functions-and-fields.patch
mm-generalize-postponed-non-root-kmem_cache-deactivation.patch
mm-introduce-__memcg_kmem_uncharge_memcg.patch
mm-unify-slab-and-slub-page-accounting.patch
mm-dont-check-the-dying-flag-on-kmem_cache-creation.patch
mm-synchronize-access-to-kmem_cache-dying-flag-using-a-spinlock.patch
mm-rework-non-root-kmem_cache-lifecycle-management.patch
mm-stop-setting-page-mem_cgroup-pointer-for-slab-pages.patch
mm-reparent-memcg-kmem_caches-on-cgroup-removal.patch
