io_uring: get rid of hashed provided buffer groups
Use a plain array for any group ID that's less than 64, and punt
anything beyond that to an xarray. 64 fits in a page even for 4KB
page sizes and with the planned additions.
This makes the expected group usage faster by avoiding a hash and lookup
to find our list, and it uses less memory upfront by not allocating any
memory for provided buffers unless it's actually being used.
Suggested-by: Pavel Begunkov <asml.silence@gmail.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
diff --git a/fs/io_uring.c b/fs/io_uring.c
index b5efabc..0672ce0 100644
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -282,7 +282,6 @@ struct io_rsrc_data {
};
struct io_buffer_list {
- struct list_head list;
struct list_head buf_list;
__u16 bgid;
};
@@ -357,7 +356,7 @@ struct io_ev_fd {
struct rcu_head rcu;
};
-#define IO_BUFFERS_HASH_BITS 5
+#define BGID_ARRAY 64
struct io_ring_ctx {
/* const or read-mostly hot data */
@@ -414,7 +413,8 @@ struct io_ring_ctx {
struct list_head timeout_list;
struct list_head ltimeout_list;
struct list_head cq_overflow_list;
- struct list_head *io_buffers;
+ struct io_buffer_list *io_bl;
+ struct xarray io_bl_xa;
struct list_head io_buffers_cache;
struct list_head apoll_cache;
struct xarray personalities;
@@ -1507,15 +1507,10 @@ static inline unsigned int io_put_kbuf(struct io_kiocb *req,
static struct io_buffer_list *io_buffer_get_list(struct io_ring_ctx *ctx,
unsigned int bgid)
{
- struct list_head *hash_list;
- struct io_buffer_list *bl;
+ if (ctx->io_bl && bgid < BGID_ARRAY)
+ return &ctx->io_bl[bgid];
- hash_list = &ctx->io_buffers[hash_32(bgid, IO_BUFFERS_HASH_BITS)];
- list_for_each_entry(bl, hash_list, list)
- if (bl->bgid == bgid || bgid == -1U)
- return bl;
-
- return NULL;
+ return xa_load(&ctx->io_bl_xa, bgid);
}
static void io_kbuf_recycle(struct io_kiocb *req, unsigned issue_flags)
@@ -1621,12 +1616,14 @@ static __cold void io_fallback_req_func(struct work_struct *work)
static __cold struct io_ring_ctx *io_ring_ctx_alloc(struct io_uring_params *p)
{
struct io_ring_ctx *ctx;
- int i, hash_bits;
+ int hash_bits;
ctx = kzalloc(sizeof(*ctx), GFP_KERNEL);
if (!ctx)
return NULL;
+ xa_init(&ctx->io_bl_xa);
+
/*
* Use 5 bits less than the max cq entries, that should give us around
* 32 entries per hash list if totally full and uniformly spread.
@@ -1648,13 +1645,6 @@ static __cold struct io_ring_ctx *io_ring_ctx_alloc(struct io_uring_params *p)
/* set invalid range, so io_import_fixed() fails meeting it */
ctx->dummy_ubuf->ubuf = -1UL;
- ctx->io_buffers = kcalloc(1U << IO_BUFFERS_HASH_BITS,
- sizeof(struct list_head), GFP_KERNEL);
- if (!ctx->io_buffers)
- goto err;
- for (i = 0; i < (1U << IO_BUFFERS_HASH_BITS); i++)
- INIT_LIST_HEAD(&ctx->io_buffers[i]);
-
if (percpu_ref_init(&ctx->refs, io_ring_ctx_ref_free,
PERCPU_REF_ALLOW_REINIT, GFP_KERNEL))
goto err;
@@ -1690,7 +1680,8 @@ static __cold struct io_ring_ctx *io_ring_ctx_alloc(struct io_uring_params *p)
err:
kfree(ctx->dummy_ubuf);
kfree(ctx->cancel_hash);
- kfree(ctx->io_buffers);
+ kfree(ctx->io_bl);
+ xa_destroy(&ctx->io_bl_xa);
kfree(ctx);
return NULL;
}
@@ -3447,15 +3438,14 @@ static int io_import_fixed(struct io_kiocb *req, int rw, struct iov_iter *iter,
return __io_import_fixed(req, rw, iter, imu);
}
-static void io_buffer_add_list(struct io_ring_ctx *ctx,
- struct io_buffer_list *bl, unsigned int bgid)
+static int io_buffer_add_list(struct io_ring_ctx *ctx,
+ struct io_buffer_list *bl, unsigned int bgid)
{
- struct list_head *list;
-
- list = &ctx->io_buffers[hash_32(bgid, IO_BUFFERS_HASH_BITS)];
- INIT_LIST_HEAD(&bl->buf_list);
bl->bgid = bgid;
- list_add(&bl->list, list);
+ if (bgid < BGID_ARRAY)
+ return 0;
+
+ return xa_err(xa_store(&ctx->io_bl_xa, bgid, bl, GFP_KERNEL));
}
static void __user *io_buffer_select(struct io_kiocb *req, size_t *len,
@@ -4921,6 +4911,23 @@ static int io_add_buffers(struct io_ring_ctx *ctx, struct io_provide_buf *pbuf,
return i ? 0 : -ENOMEM;
}
+static __cold int io_init_bl_list(struct io_ring_ctx *ctx)
+{
+ int i;
+
+ ctx->io_bl = kcalloc(BGID_ARRAY, sizeof(struct io_buffer_list),
+ GFP_KERNEL);
+ if (!ctx->io_bl)
+ return -ENOMEM;
+
+ for (i = 0; i < BGID_ARRAY; i++) {
+ INIT_LIST_HEAD(&ctx->io_bl[i].buf_list);
+ ctx->io_bl[i].bgid = i;
+ }
+
+ return 0;
+}
+
static int io_provide_buffers(struct io_kiocb *req, unsigned int issue_flags)
{
struct io_provide_buf *p = &req->pbuf;
@@ -4930,6 +4937,12 @@ static int io_provide_buffers(struct io_kiocb *req, unsigned int issue_flags)
io_ring_submit_lock(ctx, issue_flags);
+ if (unlikely(p->bgid < BGID_ARRAY && !ctx->io_bl)) {
+ ret = io_init_bl_list(ctx);
+ if (ret)
+ goto err;
+ }
+
bl = io_buffer_get_list(ctx, p->bgid);
if (unlikely(!bl)) {
bl = kmalloc(sizeof(*bl), GFP_KERNEL);
@@ -4937,7 +4950,11 @@ static int io_provide_buffers(struct io_kiocb *req, unsigned int issue_flags)
ret = -ENOMEM;
goto err;
}
- io_buffer_add_list(ctx, bl, p->bgid);
+ ret = io_buffer_add_list(ctx, bl, p->bgid);
+ if (ret) {
+ kfree(bl);
+ goto err;
+ }
}
ret = io_add_buffers(ctx, p, bl);
@@ -9931,19 +9948,19 @@ static int io_eventfd_unregister(struct io_ring_ctx *ctx)
static void io_destroy_buffers(struct io_ring_ctx *ctx)
{
+ struct io_buffer_list *bl;
+ unsigned long index;
int i;
- for (i = 0; i < (1U << IO_BUFFERS_HASH_BITS); i++) {
- struct list_head *list = &ctx->io_buffers[i];
+ for (i = 0; i < BGID_ARRAY; i++) {
+ if (!ctx->io_bl)
+ break;
+ __io_remove_buffers(ctx, &ctx->io_bl[i], -1U);
+ }
- while (!list_empty(list)) {
- struct io_buffer_list *bl;
-
- bl = list_first_entry(list, struct io_buffer_list, list);
- __io_remove_buffers(ctx, bl, -1U);
- list_del(&bl->list);
- kfree(bl);
- }
+ xa_for_each(&ctx->io_bl_xa, index, bl) {
+ xa_erase(&ctx->io_bl_xa, bl->bgid);
+ __io_remove_buffers(ctx, bl, -1U);
}
while (!list_empty(&ctx->io_buffers_pages)) {
@@ -10052,7 +10069,8 @@ static __cold void io_ring_ctx_free(struct io_ring_ctx *ctx)
io_wq_put_hash(ctx->hash_map);
kfree(ctx->cancel_hash);
kfree(ctx->dummy_ubuf);
- kfree(ctx->io_buffers);
+ kfree(ctx->io_bl);
+ xa_destroy(&ctx->io_bl_xa);
kfree(ctx);
}
@@ -11980,6 +11998,7 @@ static int __init io_uring_init(void)
/* ->buf_index is u16 */
BUILD_BUG_ON(IORING_MAX_REG_BUFFERS >= (1u << 16));
+ BUILD_BUG_ON(BGID_ARRAY * sizeof(struct io_buffer_list) > PAGE_SIZE);
/* should fit into one byte */
BUILD_BUG_ON(SQE_VALID_FLAGS >= (1 << 8));
