Skip to content

Commit

Permalink
io_uring: get rid of hashed provided buffer groups
Browse files Browse the repository at this point in the history 
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>
  • Loading branch information
Jens Axboe committed May 9, 2022
1 parent 4e90670 commit 9cfc7e9
Showing 1 changed file with 58 additions and 39 deletions.
97 changes: 58 additions & 39 deletions fs/io_uring.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -282,7 +282,6 @@ struct io_rsrc_data {
};

struct io_buffer_list {
struct list_head list;
struct list_head buf_list;
__u16 bgid;
};
Expand Down Expand Up @@ -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 */
Expand Down Expand Up @@ -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;
Expand Down Expand Up @@ -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;

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;
if (ctx->io_bl && bgid < BGID_ARRAY)
return &ctx->io_bl[bgid];

return NULL;
return xa_load(&ctx->io_bl_xa, bgid);
}

static void io_kbuf_recycle(struct io_kiocb *req, unsigned issue_flags)
Expand Down Expand Up @@ -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.
Expand All @@ -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;
Expand Down Expand Up @@ -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;
}
Expand Down Expand Up @@ -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,
Expand Down Expand Up @@ -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;
Expand All @@ -4930,14 +4937,24 @@ 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);
if (!bl) {
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);
Expand Down Expand Up @@ -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];

while (!list_empty(list)) {
struct io_buffer_list *bl;
for (i = 0; i < BGID_ARRAY; i++) {
if (!ctx->io_bl)
break;
__io_remove_buffers(ctx, &ctx->io_bl[i], -1U);
}

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)) {
Expand Down Expand Up @@ -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);
}

Expand Down Expand Up @@ -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));
Expand Down

0 comments on commit 9cfc7e9

Please sign in to comment.