io_uring: impose max limit on apoll cache

Caches like this tend to grow to the peak size, and then never get any
smaller. Impose a max limit on the size, to prevent it from growing too
big.

A somewhat randomly chosen 512 is the max size we'll allow the cache
to get. If a batch of frees come in and would bring it over that, we
simply start kfree'ing the surplus.

Signed-off-by: Jens Axboe <axboe@kernel.dk>

diff --git a/include/linux/io_uring_types.h b/include/linux/io_uring_types.h
index b548da0..bf8f953 100644 (file)
--- a/include/linux/io_uring_types.h
+++ b/include/linux/io_uring_types.h
@@ -160,6 +160,7 @@ struct io_ev_fd {
 
 struct io_alloc_cache {
        struct hlist_head       list;
+       unsigned int            nr_cached;
 };
 
 struct io_ring_ctx {

diff --git a/io_uring/alloc_cache.h b/io_uring/alloc_cache.h
index 98f2374..729793a 100644 (file)
--- a/io_uring/alloc_cache.h
+++ b/io_uring/alloc_cache.h
@@ -1,14 +1,24 @@
 #ifndef IOU_ALLOC_CACHE_H
 #define IOU_ALLOC_CACHE_H
 
+/*
+ * Don't allow the cache to grow beyond this size.
+ */
+#define IO_ALLOC_CACHE_MAX     512
+
 struct io_cache_entry {
        struct hlist_node       node;
 };
 
-static inline void io_alloc_cache_put(struct io_alloc_cache *cache,
+static inline bool io_alloc_cache_put(struct io_alloc_cache *cache,
                                      struct io_cache_entry *entry)
 {
-       hlist_add_head(&entry->node, &cache->list);
+       if (cache->nr_cached < IO_ALLOC_CACHE_MAX) {
+               cache->nr_cached++;
+               hlist_add_head(&entry->node, &cache->list);
+               return true;
+       }
+       return false;
 }
 
 static inline struct io_cache_entry *io_alloc_cache_get(struct io_alloc_cache *cache)
@@ -26,6 +36,7 @@ static inline struct io_cache_entry *io_alloc_cache_get(struct io_alloc_cache *c
 static inline void io_alloc_cache_init(struct io_alloc_cache *cache)
 {
        INIT_HLIST_HEAD(&cache->list);
+       cache->nr_cached = 0;
 }
 
 static inline void io_alloc_cache_free(struct io_alloc_cache *cache,
@@ -37,5 +48,6 @@ static inline void io_alloc_cache_free(struct io_alloc_cache *cache,
                hlist_del(node);
                free(container_of(node, struct io_cache_entry, node));
        }
+       cache->nr_cached = 0;
 }
 #endif

diff --git a/io_uring/io_uring.c b/io_uring/io_uring.c
index a360a3d..c9c23e4 100644 (file)
--- a/io_uring/io_uring.c
+++ b/io_uring/io_uring.c
@@ -1181,7 +1181,8 @@ void io_free_batch_list(struct io_ring_ctx *ctx, struct io_wq_work_node *node)
 
                                if (apoll->double_poll)
                                        kfree(apoll->double_poll);
-                               io_alloc_cache_put(&ctx->apoll_cache, &apoll->cache);
+                               if (!io_alloc_cache_put(&ctx->apoll_cache, &apoll->cache))
+                                       kfree(apoll);
                                req->flags &= ~REQ_F_POLLED;
                        }
                        if (req->flags & IO_REQ_LINK_FLAGS)