On large systems, when some slab caches grow to millions of objects (and
many gigabytes), running 'cat /proc/slabinfo' can take up to 1-2 seconds.
During this time, interrupts are disabled while walking the slab lists
(slabs_full, slabs_partial, and slabs_free) for each node, and this
sometimes causes timeouts in other drivers (for instance, Infiniband).
This patch optimizes 'cat /proc/slabinfo' by maintaining a counter for
total number of allocated slabs per node, per cache. This counter is
updated when a slab is created or destroyed. This enables us to skip
traversing the slabs_full list while gathering slabinfo statistics, and
since slabs_full tends to be the biggest list when the cache is large, it
results in a dramatic performance improvement. Getting slabinfo statistics
now only requires walking the slabs_free and slabs_partial lists, and
those lists are usually much smaller than slabs_full. We tested this after
growing the dentry cache to 70GB, and the performance improved from 2s to
5ms.
Signed-off-by: Aruna Ramakrishna <aruna.ramakrishna@xxxxxxxxxx>
Cc: Mike Kravetz <mike.kravetz@xxxxxxxxxx>
Cc: Christoph Lameter <cl@xxxxxxxxx>
Cc: Pekka Enberg <penberg@xxxxxxxxxx>
Cc: David Rientjes <rientjes@xxxxxxxxxx>
Cc: Joonsoo Kim <iamjoonsoo.kim@xxxxxxx>
Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
Note: this has been tested only on x86_64.
mm/slab.c | 25 ++++++++++++++++---------
mm/slab.h | 15 ++++++++++++++-
mm/slub.c | 19 +------------------
3 files changed, 31 insertions(+), 28 deletions(-)
diff --git a/mm/slab.c b/mm/slab.c
index 261147b..d683840 100644
--- a/mm/slab.c
+++ b/mm/slab.c
@@ -233,6 +233,7 @@ static void kmem_cache_node_init(struct kmem_cache_node *parent)
spin_lock_init(&parent->list_lock);
parent->free_objects = 0;
parent->free_touched = 0;
+ atomic_long_set(&parent->nr_slabs, 0);
}
#define MAKE_LIST(cachep, listp, slab, nodeid) \
@@ -2333,6 +2334,7 @@ static int drain_freelist(struct kmem_cache *cache,
n->free_objects -= cache->num;
spin_unlock_irq(&n->list_lock);
slab_destroy(cache, page);
+ atomic_long_dec(&n->nr_slabs);
nr_freed++;
}
out:
@@ -2736,6 +2738,8 @@ static struct page *cache_grow_begin(struct kmem_cache *cachep,
if (gfpflags_allow_blocking(local_flags))
local_irq_disable();
+ atomic_long_inc(&n->nr_slabs);
+
return page;
opps1:
@@ -3455,6 +3459,7 @@ static void free_block(struct kmem_cache *cachep, void **objpp,
page = list_last_entry(&n->slabs_free, struct page, lru);
list_move(&page->lru, list);
+ atomic_long_dec(&n->nr_slabs);
}
}
@@ -4111,6 +4116,8 @@ void get_slabinfo(struct kmem_cache *cachep, struct slabinfo *sinfo)
unsigned long num_objs;
unsigned long active_slabs = 0;
unsigned long num_slabs, free_objects = 0, shared_avail = 0;
+ unsigned long num_slabs_partial = 0, num_slabs_free = 0;
+ unsigned long num_slabs_full = 0;
const char *name;
char *error = NULL;
int node;
@@ -4120,36 +4127,36 @@ void get_slabinfo(struct kmem_cache *cachep, struct slabinfo *sinfo)
num_slabs = 0;
for_each_kmem_cache_node(cachep, node, n) {
+ num_slabs += node_nr_slabs(n);
check_irq_on();
spin_lock_irq(&n->list_lock);
- list_for_each_entry(page, &n->slabs_full, lru) {
- if (page->active != cachep->num && !error)
- error = "slabs_full accounting error";
- active_objs += cachep->num;
- active_slabs++;
- }
list_for_each_entry(page, &n->slabs_partial, lru) {
if (page->active == cachep->num && !error)
error = "slabs_partial accounting error";
if (!page->active && !error)
error = "slabs_partial accounting error";
active_objs += page->active;
- active_slabs++;
+ num_slabs_partial++;
}
+
list_for_each_entry(page, &n->slabs_free, lru) {
if (page->active && !error)
error = "slabs_free accounting error";
- num_slabs++;
+ num_slabs_free++;
}
+
free_objects += n->free_objects;
if (n->shared)
shared_avail += n->shared->avail;
spin_unlock_irq(&n->list_lock);
}
- num_slabs += active_slabs;
num_objs = num_slabs * cachep->num;
+ active_slabs = num_slabs - num_slabs_free;
+ num_slabs_full = num_slabs - (num_slabs_partial + num_slabs_free);
+ active_objs += (num_slabs_full * cachep->num);
+
if (num_objs - active_objs != free_objects && !error)
error = "free_objects accounting error";
diff --git a/mm/slab.h b/mm/slab.h
index 9653f2e..5740cec 100644
--- a/mm/slab.h
+++ b/mm/slab.h
@@ -427,6 +427,7 @@ static inline void slab_post_alloc_hook(struct kmem_cache *s, gfp_t flags,
*/
struct kmem_cache_node {
spinlock_t list_lock;
+ atomic_long_t nr_slabs;
#ifdef CONFIG_SLAB
struct list_head slabs_partial; /* partial list first, better asm code */
@@ -445,7 +446,6 @@ struct kmem_cache_node {
unsigned long nr_partial;
struct list_head partial;
#ifdef CONFIG_SLUB_DEBUG
- atomic_long_t nr_slabs;
atomic_long_t total_objects;
struct list_head full;
#endif
@@ -458,6 +458,19 @@ static inline struct kmem_cache_node *get_node(struct kmem_cache *s, int node)
return s->node[node];
}
+/* Tracking of the number of slabs for /proc/slabinfo and debugging purposes */
+static inline unsigned long slabs_node(struct kmem_cache *s, int node)
+{
+ struct kmem_cache_node *n = get_node(s, node);
+
+ return atomic_long_read(&n->nr_slabs);
+}
+
+static inline unsigned long node_nr_slabs(struct kmem_cache_node *n)
+{
+ return atomic_long_read(&n->nr_slabs);
+}
+
/*
* Iterator over all nodes. The body will be executed for each node that has
* a kmem_cache_node structure allocated (which is true for all online nodes)
diff --git a/mm/slub.c b/mm/slub.c
index 26eb6a99..b9f2607 100644
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -1006,19 +1006,6 @@ static void remove_full(struct kmem_cache *s, struct kmem_cache_node *n, struct
list_del(&page->lru);
}
-/* Tracking of the number of slabs for debugging purposes */
-static inline unsigned long slabs_node(struct kmem_cache *s, int node)
-{
- struct kmem_cache_node *n = get_node(s, node);
-
- return atomic_long_read(&n->nr_slabs);
-}
-
-static inline unsigned long node_nr_slabs(struct kmem_cache_node *n)
-{
- return atomic_long_read(&n->nr_slabs);
-}
-
static inline void inc_slabs_node(struct kmem_cache *s, int node, int objects)
{
struct kmem_cache_node *n = get_node(s, node);
@@ -1297,10 +1284,6 @@ unsigned long kmem_cache_flags(unsigned long object_size,
#define disable_higher_order_debug 0
-static inline unsigned long slabs_node(struct kmem_cache *s, int node)
- { return 0; }
-static inline unsigned long node_nr_slabs(struct kmem_cache_node *n)
- { return 0; }
static inline void inc_slabs_node(struct kmem_cache *s, int node,
int objects) {}
static inline void dec_slabs_node(struct kmem_cache *s, int node,
@@ -3258,8 +3241,8 @@ init_kmem_cache_node(struct kmem_cache_node *n)
n->nr_partial = 0;
spin_lock_init(&n->list_lock);
INIT_LIST_HEAD(&n->partial);
-#ifdef CONFIG_SLUB_DEBUG
atomic_long_set(&n->nr_slabs, 0);
+#ifdef CONFIG_SLUB_DEBUG
atomic_long_set(&n->total_objects, 0);
INIT_LIST_HEAD(&n->full);
#endif
--
1.8.3.1
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