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mm/slab: improve performance of gathering slabinfo stats

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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>
This commit is contained in:
Aruna Ramakrishna 2016-10-27 17:46:32 -07:00 committed by Linus Torvalds
parent 1f84a18fc0
commit 07a63c41fa
2 changed files with 28 additions and 16 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

43
mm/slab.c
View File

@ -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";

1
mm/slab.h
View File

@ -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 */