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slab: defer slab_destroy in free_block()
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In free_block(), if freeing object makes new free slab and number of
free_objects exceeds free_limit, we start to destroy this new free slab
with holding the kmem_cache node lock.  Holding the lock is useless and,
generally, holding a lock as least as possible is good thing.  I never
measure performance effect of this, but we'd be better not to hold the
lock as much as possible.

Commented by Christoph:
  This is also good because kmem_cache_free is no longer called while
  holding the node lock. So we avoid one case of recursion.

Signed-off-by: Joonsoo Kim <[email protected]>
Acked-by: Christoph Lameter <[email protected]>
Cc: Pekka Enberg <[email protected]>
Acked-by: David Rientjes <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>
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@JoonsooKim @torvalds
JoonsooKim authored and torvalds committed Aug 7, 2014
1 parent 25c063f commit 97654df
Showing 1 changed file with 41 additions and 19 deletions.
60 changes: 41 additions & 19 deletions mm/slab.c
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Original file line number Diff line number Diff line change
Expand Up @@ -242,7 +242,8 @@ static struct kmem_cache_node __initdata init_kmem_cache_node[NUM_INIT_LISTS];
static int drain_freelist(struct kmem_cache *cache,
struct kmem_cache_node *n, int tofree);
static void free_block(struct kmem_cache *cachep, void **objpp, int len,
int node);
int node, struct list_head *list);
static void slabs_destroy(struct kmem_cache *cachep, struct list_head *list);
static int enable_cpucache(struct kmem_cache *cachep, gfp_t gfp);
static void cache_reap(struct work_struct *unused);

Expand Down Expand Up @@ -1030,6 +1031,7 @@ static void __drain_alien_cache(struct kmem_cache *cachep,
struct array_cache *ac, int node)
{
struct kmem_cache_node *n = get_node(cachep, node);
LIST_HEAD(list);

if (ac->avail) {
spin_lock(&n->list_lock);
Expand All @@ -1041,9 +1043,10 @@ static void __drain_alien_cache(struct kmem_cache *cachep,
if (n->shared)
transfer_objects(n->shared, ac, ac->limit);

free_block(cachep, ac->entry, ac->avail, node);
free_block(cachep, ac->entry, ac->avail, node, &list);
ac->avail = 0;
spin_unlock(&n->list_lock);
slabs_destroy(cachep, &list);
}
}

Expand Down Expand Up @@ -1087,6 +1090,7 @@ static inline int cache_free_alien(struct kmem_cache *cachep, void *objp)
struct kmem_cache_node *n;
struct array_cache *alien = NULL;
int node;
LIST_HEAD(list);

node = numa_mem_id();

Expand All @@ -1111,8 +1115,9 @@ static inline int cache_free_alien(struct kmem_cache *cachep, void *objp)
} else {
n = get_node(cachep, nodeid);
spin_lock(&n->list_lock);
free_block(cachep, &objp, 1, nodeid);
free_block(cachep, &objp, 1, nodeid, &list);
spin_unlock(&n->list_lock);
slabs_destroy(cachep, &list);
}
return 1;
}
Expand Down Expand Up @@ -1182,6 +1187,7 @@ static void cpuup_canceled(long cpu)
struct array_cache *nc;
struct array_cache *shared;
struct array_cache **alien;
LIST_HEAD(list);

/* cpu is dead; no one can alloc from it. */
nc = cachep->array[cpu];
Expand All @@ -1196,7 +1202,7 @@ static void cpuup_canceled(long cpu)
/* Free limit for this kmem_cache_node */
n->free_limit -= cachep->batchcount;
if (nc)
free_block(cachep, nc->entry, nc->avail, node);
free_block(cachep, nc->entry, nc->avail, node, &list);

if (!cpumask_empty(mask)) {
spin_unlock_irq(&n->list_lock);
Expand All @@ -1206,7 +1212,7 @@ static void cpuup_canceled(long cpu)
shared = n->shared;
if (shared) {
free_block(cachep, shared->entry,
shared->avail, node);
shared->avail, node, &list);
n->shared = NULL;
}

Expand All @@ -1221,6 +1227,7 @@ static void cpuup_canceled(long cpu)
free_alien_cache(alien);
}
free_array_cache:
slabs_destroy(cachep, &list);
kfree(nc);
}
/*
Expand Down Expand Up @@ -2056,6 +2063,16 @@ static void slab_destroy(struct kmem_cache *cachep, struct page *page)
kmem_cache_free(cachep->freelist_cache, freelist);
}

static void slabs_destroy(struct kmem_cache *cachep, struct list_head *list)
{
struct page *page, *n;

list_for_each_entry_safe(page, n, list, lru) {
list_del(&page->lru);
slab_destroy(cachep, page);
}
}

/**
* calculate_slab_order - calculate size (page order) of slabs
* @cachep: pointer to the cache that is being created
Expand Down Expand Up @@ -2459,13 +2476,15 @@ static void do_drain(void *arg)
struct array_cache *ac;
int node = numa_mem_id();
struct kmem_cache_node *n;
LIST_HEAD(list);

check_irq_off();
ac = cpu_cache_get(cachep);
n = get_node(cachep, node);
spin_lock(&n->list_lock);
free_block(cachep, ac->entry, ac->avail, node);
free_block(cachep, ac->entry, ac->avail, node, &list);
spin_unlock(&n->list_lock);
slabs_destroy(cachep, &list);
ac->avail = 0;
}

Expand Down Expand Up @@ -3393,9 +3412,10 @@ slab_alloc(struct kmem_cache *cachep, gfp_t flags, unsigned long caller)

/*
* Caller needs to acquire correct kmem_cache_node's list_lock
* @list: List of detached free slabs should be freed by caller
*/
static void free_block(struct kmem_cache *cachep, void **objpp, int nr_objects,
int node)
static void free_block(struct kmem_cache *cachep, void **objpp,
int nr_objects, int node, struct list_head *list)
{
int i;
struct kmem_cache_node *n = get_node(cachep, node);
Expand All @@ -3418,13 +3438,7 @@ static void free_block(struct kmem_cache *cachep, void **objpp, int nr_objects,
if (page->active == 0) {
if (n->free_objects > n->free_limit) {
n->free_objects -= cachep->num;
/* No need to drop any previously held
* lock here, even if we have a off-slab slab
* descriptor it is guaranteed to come from
* a different cache, refer to comments before
* alloc_slabmgmt.
*/
slab_destroy(cachep, page);
list_add_tail(&page->lru, list);
} else {
list_add(&page->lru, &n->slabs_free);
}
Expand All @@ -3443,6 +3457,7 @@ static void cache_flusharray(struct kmem_cache *cachep, struct array_cache *ac)
int batchcount;
struct kmem_cache_node *n;
int node = numa_mem_id();
LIST_HEAD(list);

batchcount = ac->batchcount;
#if DEBUG
Expand All @@ -3464,7 +3479,7 @@ static void cache_flusharray(struct kmem_cache *cachep, struct array_cache *ac)
}
}

free_block(cachep, ac->entry, batchcount, node);
free_block(cachep, ac->entry, batchcount, node, &list);
free_done:
#if STATS
{
Expand All @@ -3485,6 +3500,7 @@ static void cache_flusharray(struct kmem_cache *cachep, struct array_cache *ac)
}
#endif
spin_unlock(&n->list_lock);
slabs_destroy(cachep, &list);
ac->avail -= batchcount;
memmove(ac->entry, &(ac->entry[batchcount]), sizeof(void *)*ac->avail);
}
Expand Down Expand Up @@ -3765,12 +3781,13 @@ static int alloc_kmem_cache_node(struct kmem_cache *cachep, gfp_t gfp)
n = get_node(cachep, node);
if (n) {
struct array_cache *shared = n->shared;
LIST_HEAD(list);

spin_lock_irq(&n->list_lock);

if (shared)
free_block(cachep, shared->entry,
shared->avail, node);
shared->avail, node, &list);

n->shared = new_shared;
if (!n->alien) {
Expand All @@ -3780,6 +3797,7 @@ static int alloc_kmem_cache_node(struct kmem_cache *cachep, gfp_t gfp)
n->free_limit = (1 + nr_cpus_node(node)) *
cachep->batchcount + cachep->num;
spin_unlock_irq(&n->list_lock);
slabs_destroy(cachep, &list);
kfree(shared);
free_alien_cache(new_alien);
continue;
Expand Down Expand Up @@ -3869,6 +3887,7 @@ static int __do_tune_cpucache(struct kmem_cache *cachep, int limit,
cachep->shared = shared;

for_each_online_cpu(i) {
LIST_HEAD(list);
struct array_cache *ccold = new->new[i];
int node;
struct kmem_cache_node *n;
Expand All @@ -3879,8 +3898,9 @@ static int __do_tune_cpucache(struct kmem_cache *cachep, int limit,
node = cpu_to_mem(i);
n = get_node(cachep, node);
spin_lock_irq(&n->list_lock);
free_block(cachep, ccold->entry, ccold->avail, node);
free_block(cachep, ccold->entry, ccold->avail, node, &list);
spin_unlock_irq(&n->list_lock);
slabs_destroy(cachep, &list);
kfree(ccold);
}
kfree(new);
Expand Down Expand Up @@ -3988,6 +4008,7 @@ static int enable_cpucache(struct kmem_cache *cachep, gfp_t gfp)
static void drain_array(struct kmem_cache *cachep, struct kmem_cache_node *n,
struct array_cache *ac, int force, int node)
{
LIST_HEAD(list);
int tofree;

if (!ac || !ac->avail)
Expand All @@ -4000,12 +4021,13 @@ static void drain_array(struct kmem_cache *cachep, struct kmem_cache_node *n,
tofree = force ? ac->avail : (ac->limit + 4) / 5;
if (tofree > ac->avail)
tofree = (ac->avail + 1) / 2;
free_block(cachep, ac->entry, tofree, node);
free_block(cachep, ac->entry, tofree, node, &list);
ac->avail -= tofree;
memmove(ac->entry, &(ac->entry[tofree]),
sizeof(void *) * ac->avail);
}
spin_unlock_irq(&n->list_lock);
slabs_destroy(cachep, &list);
}
}

Expand Down

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