io_uring/rsrc: add custom limit for node caching

The number of entries in the rsrc node cache is limited to 512, which
still seems unnecessarily large. Add per cache thresholds and set to
to 32 for the rsrc node cache.
Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
Link: https://lore.kernel.org/r/d0cd538b944dac0bf878e276fc0199f21e6bccea.1680576071.git.asml.silence@gmail.comSigned-off-by: Jens Axboe <axboe@kernel.dk>

include/linux/io_uring_types.h

@@ -190,6 +190,7 @@ struct io_ev_fd {
 struct io_alloc_cache {
 	struct io_wq_work_node	list;
 	unsigned int		nr_cached;
+	unsigned int		max_cached;
 	size_t			elem_size;
 };
 

io_uring/alloc_cache.h

@@ -13,7 +13,7 @@ struct io_cache_entry {
 static inline bool io_alloc_cache_put(struct io_alloc_cache *cache,
 				      struct io_cache_entry *entry)
 {
-	if (cache->nr_cached < IO_ALLOC_CACHE_MAX) {
+	if (cache->nr_cached < cache->max_cached) {
 		cache->nr_cached++;
 		wq_stack_add_head(&entry->node, &cache->list);
 		/* KASAN poisons object */
@@ -38,10 +38,12 @@ static inline struct io_cache_entry *io_alloc_cache_get(struct io_alloc_cache *c
 	return NULL;
 }
 
-static inline void io_alloc_cache_init(struct io_alloc_cache *cache, size_t size)
+static inline void io_alloc_cache_init(struct io_alloc_cache *cache,
+				       unsigned max_nr, size_t size)
 {
 	cache->list.next = NULL;
 	cache->nr_cached = 0;
+	cache->max_cached = max_nr;
 	cache->elem_size = size;
 }
 

io_uring/io_uring.c

@@ -310,9 +310,12 @@ static __cold struct io_ring_ctx *io_ring_ctx_alloc(struct io_uring_params *p)
 	INIT_LIST_HEAD(&ctx->sqd_list);
 	INIT_LIST_HEAD(&ctx->cq_overflow_list);
 	INIT_LIST_HEAD(&ctx->io_buffers_cache);
-	io_alloc_cache_init(&ctx->rsrc_node_cache, sizeof(struct io_rsrc_node));
-	io_alloc_cache_init(&ctx->apoll_cache, sizeof(struct async_poll));
-	io_alloc_cache_init(&ctx->netmsg_cache, sizeof(struct io_async_msghdr));
+	io_alloc_cache_init(&ctx->rsrc_node_cache, IO_NODE_ALLOC_CACHE_MAX,
+			    sizeof(struct io_rsrc_node));
+	io_alloc_cache_init(&ctx->apoll_cache, IO_ALLOC_CACHE_MAX,
+			    sizeof(struct async_poll));
+	io_alloc_cache_init(&ctx->netmsg_cache, IO_ALLOC_CACHE_MAX,
+			    sizeof(struct io_async_msghdr));
 	init_completion(&ctx->ref_comp);
 	xa_init_flags(&ctx->personalities, XA_FLAGS_ALLOC1);
 	mutex_init(&ctx->uring_lock);

io_uring/rsrc.h

@@ -6,6 +6,8 @@
 
 #include "alloc_cache.h"
 
+#define IO_NODE_ALLOC_CACHE_MAX 32
+
 #define IO_RSRC_TAG_TABLE_SHIFT	(PAGE_SHIFT - 3)
 #define IO_RSRC_TAG_TABLE_MAX	(1U << IO_RSRC_TAG_TABLE_SHIFT)
 #define IO_RSRC_TAG_TABLE_MASK	(IO_RSRC_TAG_TABLE_MAX - 1)