Commit b8fb5b4f authored by Pavel Begunkov's avatar Pavel Begunkov Committed by Jens Axboe
Browse files

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: default avatarPavel Begunkov <asml.silence@gmail.com>
Link: https://lore.kernel.org/r/e9ed8a9457b331a26555ff9443afc64cdaab7247.1680576071.git.asml.silence@gmail.com


Signed-off-by: default avatarJens Axboe <axboe@kernel.dk>
parent e3ef728f

io_uring/rsrc.c

+5 −10
Original line number Diff line number Diff line
@@ -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;

	}

io_uring/rsrc.h

+4 −2
Original line number Diff line number Diff line
@@ -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)