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 | 43 +++++++++++++++++++++++++++----------------
mm/slab.h | 1 +
2 files changed, 28 insertions(+), 16 deletions(-)
diff --git a/mm/slab.c b/mm/slab.c
index b672710..042017e 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;
+ parent->num_slabs = 0;
}
#define MAKE_LIST(cachep, listp, slab, nodeid) \
@@ -1394,24 +1395,27 @@ slab_out_of_memory(struct kmem_cache *cachep, gfp_t gfpflags, int nodeid)
for_each_kmem_cache_node(cachep, node, n) {
unsigned long active_objs = 0, num_objs = 0, free_objects = 0;
unsigned long active_slabs = 0, num_slabs = 0;
+ unsigned long num_slabs_partial = 0, num_slabs_free = 0;
+ unsigned long num_slabs_full;
spin_lock_irqsave(&n->list_lock, flags);
- list_for_each_entry(page, &n->slabs_full, lru) {
- active_objs += cachep->num;
- active_slabs++;
- }
+ num_slabs = n->num_slabs;
list_for_each_entry(page, &n->slabs_partial, lru) {
active_objs += page->active;
- active_slabs++;
+ num_slabs_partial++;
}
list_for_each_entry(page, &n->slabs_free, lru)
- num_slabs++;
+ num_slabs_free++;
free_objects += n->free_objects;
spin_unlock_irqrestore(&n->list_lock, flags);
- 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);
+
pr_warn(" node %d: slabs: %ld/%ld, objs: %ld/%ld, free: %ld\n",
node, active_slabs, num_slabs, active_objs, num_objs,
free_objects);
@@ -2326,6 +2330,7 @@ static int drain_freelist(struct kmem_cache *cache,
page = list_entry(p, struct page, lru);
list_del(&page->lru);
+ n->num_slabs--;
/*
* Safe to drop the lock. The slab is no longer linked
* to the cache.
@@ -2764,6 +2769,8 @@ static void cache_grow_end(struct kmem_cache *cachep, struct page *page)
list_add_tail(&page->lru, &(n->slabs_free));
else
fixup_slab_list(cachep, n, page, &list);
+
+ n->num_slabs++;
STATS_INC_GROWN(cachep);
n->free_objects += cachep->num - page->active;
spin_unlock(&n->list_lock);
@@ -3455,6 +3462,7 @@ 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);
+ n->num_slabs--;
}
}
@@ -4111,6 +4119,8 @@ 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;
@@ -4123,33 +4133,34 @@ void get_slabinfo(struct kmem_cache *cachep, struct slabinfo *sinfo)
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++;
- }
+ num_slabs += n->num_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..bc05fdc 100644
--- a/mm/slab.h
+++ b/mm/slab.h
@@ -432,6 +432,7 @@ struct kmem_cache_node {
struct list_head slabs_partial; /* partial list first, better asm code */
struct list_head slabs_full;
struct list_head slabs_free;
+ unsigned long num_slabs;
unsigned long free_objects;
unsigned int free_limit;
unsigned int colour_next; /* Per-node cache coloring */
--
1.8.3.1
--
To unsubscribe, send a message with 'unsubscribe linux-mm' in
the body to majordomo@xxxxxxxxx. For more info on Linux MM,
see: http://www.linux-mm.org/ .
Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>