[PATCH 01/11] io_uring/rsrc: use non-pcpu refcounts for nodes

Pavel Begunkov
2023-03-30T14:54:37Z

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>
---
io_uring/rsrc.c | 15 +++++----------
io_uring/rsrc.h | 6 ++++--
2 files changed, 9 insertions(+), 12 deletions(-)

diff --git a/io_uring/rsrc.c b/io_uring/rsrc.c
index 7a43aed8e395..f2da9e251e3f 100644
--- 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 f27f4975217d..1467b31843bc 100644
--- 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)
--
2.39.1