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Commit 07a63c41 authored by Aruna Ramakrishna's avatar Aruna Ramakrishna Committed by Linus Torvalds
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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: default avatarAruna Ramakrishna <aruna.ramakrishna@oracle.com>
Acked-by: default avatarDavid 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: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 1f84a18f

mm/slab.c

+27 −16
Original line number Diff line number Diff line
@@ -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";

mm/slab.h

+1 −0
Original line number Diff line number Diff line
@@ -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 */