diff options
Diffstat (limited to 'mm/shrinker.c')
-rw-r--r-- | mm/shrinker.c | 89 |
1 files changed, 68 insertions, 21 deletions
diff --git a/mm/shrinker.c b/mm/shrinker.c index e2e832b15803..9bb2e61092b3 100644 --- a/mm/shrinker.c +++ b/mm/shrinker.c @@ -2,6 +2,7 @@ #include <linux/memcontrol.h> #include <linux/rwsem.h> #include <linux/shrinker.h> +#include <linux/rculist.h> #include <trace/events/vmscan.h> #include "internal.h" @@ -577,33 +578,50 @@ unsigned long shrink_slab(gfp_t gfp_mask, int nid, struct mem_cgroup *memcg, if (!mem_cgroup_disabled() && !mem_cgroup_is_root(memcg)) return shrink_slab_memcg(gfp_mask, nid, memcg, priority); - if (!down_read_trylock(&shrinker_rwsem)) - goto out; - - list_for_each_entry(shrinker, &shrinker_list, list) { + /* + * lockless algorithm of global shrink. + * + * In the unregistration setp, the shrinker will be freed asynchronously + * via RCU after its refcount reaches 0. So both rcu_read_lock() and + * shrinker_try_get() can be used to ensure the existence of the shrinker. + * + * So in the global shrink: + * step 1: use rcu_read_lock() to guarantee existence of the shrinker + * and the validity of the shrinker_list walk. + * step 2: use shrinker_try_get() to try get the refcount, if successful, + * then the existence of the shrinker can also be guaranteed, + * so we can release the RCU lock to do do_shrink_slab() that + * may sleep. + * step 3: *MUST* to reacquire the RCU lock before calling shrinker_put(), + * which ensures that neither this shrinker nor the next shrinker + * will be freed in the next traversal operation. + * step 4: do shrinker_put() paired with step 2 to put the refcount, + * if the refcount reaches 0, then wake up the waiter in + * shrinker_free() by calling complete(). + */ + rcu_read_lock(); + list_for_each_entry_rcu(shrinker, &shrinker_list, list) { struct shrink_control sc = { .gfp_mask = gfp_mask, .nid = nid, .memcg = memcg, }; + if (!shrinker_try_get(shrinker)) + continue; + + rcu_read_unlock(); + ret = do_shrink_slab(&sc, shrinker, priority); if (ret == SHRINK_EMPTY) ret = 0; freed += ret; - /* - * Bail out if someone want to register a new shrinker to - * prevent the registration from being stalled for long periods - * by parallel ongoing shrinking. - */ - if (rwsem_is_contended(&shrinker_rwsem)) { - freed = freed ? : 1; - break; - } + + rcu_read_lock(); + shrinker_put(shrinker); } - up_read(&shrinker_rwsem); -out: + rcu_read_unlock(); cond_resched(); return freed; } @@ -676,13 +694,29 @@ void shrinker_register(struct shrinker *shrinker) } down_write(&shrinker_rwsem); - list_add_tail(&shrinker->list, &shrinker_list); + list_add_tail_rcu(&shrinker->list, &shrinker_list); shrinker->flags |= SHRINKER_REGISTERED; shrinker_debugfs_add(shrinker); up_write(&shrinker_rwsem); + + init_completion(&shrinker->done); + /* + * Now the shrinker is fully set up, take the first reference to it to + * indicate that lookup operations are now allowed to use it via + * shrinker_try_get(). + */ + refcount_set(&shrinker->refcount, 1); } EXPORT_SYMBOL_GPL(shrinker_register); +static void shrinker_free_rcu_cb(struct rcu_head *head) +{ + struct shrinker *shrinker = container_of(head, struct shrinker, rcu); + + kfree(shrinker->nr_deferred); + kfree(shrinker); +} + void shrinker_free(struct shrinker *shrinker) { struct dentry *debugfs_entry = NULL; @@ -691,9 +725,25 @@ void shrinker_free(struct shrinker *shrinker) if (!shrinker) return; + if (shrinker->flags & SHRINKER_REGISTERED) { + /* drop the initial refcount */ + shrinker_put(shrinker); + /* + * Wait for all lookups of the shrinker to complete, after that, + * no shrinker is running or will run again, then we can safely + * free it asynchronously via RCU and safely free the structure + * where the shrinker is located, such as super_block etc. + */ + wait_for_completion(&shrinker->done); + } + down_write(&shrinker_rwsem); if (shrinker->flags & SHRINKER_REGISTERED) { - list_del(&shrinker->list); + /* + * Now we can safely remove it from the shrinker_list and then + * free it. + */ + list_del_rcu(&shrinker->list); debugfs_entry = shrinker_debugfs_detach(shrinker, &debugfs_id); shrinker->flags &= ~SHRINKER_REGISTERED; } @@ -707,9 +757,6 @@ void shrinker_free(struct shrinker *shrinker) if (debugfs_entry) shrinker_debugfs_remove(debugfs_entry, debugfs_id); - kfree(shrinker->nr_deferred); - shrinker->nr_deferred = NULL; - - kfree(shrinker); + call_rcu(&shrinker->rcu, shrinker_free_rcu_cb); } EXPORT_SYMBOL_GPL(shrinker_free); |