io_uring/rsrc: use non-pcpu refcounts for nodes

One problem with the current rsrc infra is that often updates will
generates lots of rsrc nodes, each carry pcpu refs. That takes quite a
lot of memory, especially if there is a stall, and takes lots of CPU
cycles. Only pcpu allocations takes >50 of CPU with a naive benchmark
updating files in a loop.

Replace pcpu refs with normal refcounting. There is already a hot path
avoiding atomics / refs, but following patches will further improve it.

Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
Link: https://lore.kernel.org/r/e9ed8a9457b331a26555ff9443afc64cdaab7247.1680576071.git.asml.silence@gmail.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>

diff --git a/io_uring/rsrc.c b/io_uring/rsrc.c
index 7a43aed..f2da9e2 100644 (file)
--- a/io_uring/rsrc.c
+++ b/io_uring/rsrc.c
@@ -155,7 +155,7 @@ void io_rsrc_refs_refill(struct io_ring_ctx *ctx)
        __must_hold(&ctx->uring_lock)
 {
        ctx->rsrc_cached_refs += IO_RSRC_REF_BATCH;
-       percpu_ref_get_many(&ctx->rsrc_node->refs, IO_RSRC_REF_BATCH);
+       refcount_add(IO_RSRC_REF_BATCH, &ctx->rsrc_node->refs);
 }
 
 static void __io_rsrc_put_work(struct io_rsrc_node *ref_node)
@@ -220,13 +220,11 @@ void io_wait_rsrc_data(struct io_rsrc_data *data)
 
 void io_rsrc_node_destroy(struct io_rsrc_node *ref_node)
 {
-       percpu_ref_exit(&ref_node->refs);
        kfree(ref_node);
 }
 
-static __cold void io_rsrc_node_ref_zero(struct percpu_ref *ref)
+__cold void io_rsrc_node_ref_zero(struct io_rsrc_node *node)
 {
-       struct io_rsrc_node *node = container_of(ref, struct io_rsrc_node, refs);
        struct io_ring_ctx *ctx = node->rsrc_data->ctx;
        unsigned long flags;
        bool first_add = false;
@@ -269,11 +267,7 @@ static struct io_rsrc_node *io_rsrc_node_alloc(void)
        if (!ref_node)
                return NULL;
 
-       if (percpu_ref_init(&ref_node->refs, io_rsrc_node_ref_zero,
-                           0, GFP_KERNEL)) {
-               kfree(ref_node);
-               return NULL;
-       }
+       refcount_set(&ref_node->refs, 1);
        INIT_LIST_HEAD(&ref_node->node);
        INIT_LIST_HEAD(&ref_node->rsrc_list);
        ref_node->done = false;
@@ -298,7 +292,8 @@ void io_rsrc_node_switch(struct io_ring_ctx *ctx,
                spin_unlock_irq(&ctx->rsrc_ref_lock);
 
                atomic_inc(&data_to_kill->refs);
-               percpu_ref_kill(&rsrc_node->refs);
+               /* put master ref */
+               io_rsrc_put_node(rsrc_node, 1);
                ctx->rsrc_node = NULL;
        }
 

diff --git a/io_uring/rsrc.h b/io_uring/rsrc.h
index f27f497..1467b31 100644 (file)
--- a/io_uring/rsrc.h
+++ b/io_uring/rsrc.h
@@ -37,7 +37,7 @@ struct io_rsrc_data {
 };
 
 struct io_rsrc_node {
-       struct percpu_ref               refs;
+       refcount_t                      refs;
        struct list_head                node;
        struct list_head                rsrc_list;
        struct io_rsrc_data             *rsrc_data;
@@ -54,6 +54,7 @@ struct io_mapped_ubuf {
 };
 
 void io_rsrc_put_tw(struct callback_head *cb);
+void io_rsrc_node_ref_zero(struct io_rsrc_node *node);
 void io_rsrc_put_work(struct work_struct *work);
 void io_rsrc_refs_refill(struct io_ring_ctx *ctx);
 void io_wait_rsrc_data(struct io_rsrc_data *data);
@@ -109,7 +110,8 @@ int io_register_rsrc(struct io_ring_ctx *ctx, void __user *arg,
 
 static inline void io_rsrc_put_node(struct io_rsrc_node *node, int nr)
 {
-       percpu_ref_put_many(&node->refs, nr);
+       if (refcount_sub_and_test(nr, &node->refs))
+               io_rsrc_node_ref_zero(node);
 }
 
 static inline void io_req_put_rsrc(struct io_kiocb *req)