mm/slab: improve performance of gathering slabinfo stats

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.

Link: http://lkml.kernel.org/r/1472517876-26814-1-git-send-email-aruna.ramakrishna@oracle.com
Signed-off-by: Aruna Ramakrishna <aruna.ramakrishna@oracle.com>
Acked-by: David Rientjes <rientjes@google.com>
Cc: Mike Kravetz <mike.kravetz@oracle.com>
Cc: Christoph Lameter <cl@linux.com>
Cc: Pekka Enberg <penberg@kernel.org>
Cc: David Rientjes <rientjes@google.com>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 27 insertions, 16 deletions

diff --git a/mm/slab.c b/mm/slab.c
index c451e3f6bbf6..0b0550ca85b4 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)                          \
@@ -1382,24 +1383,27 @@ 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);
@@ -2314,6 +2318,7 @@ 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.
@@ -2752,6 +2757,8 @@ 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);
@@ -3443,6 +3450,7 @@ 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--;
         }
 }
 
@@ -4099,6 +4107,8 @@ 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;
@@ -4111,33 +4121,34 @@ 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";