Commit 4a07723f authored by Pavel Begunkov's avatar Pavel Begunkov Committed by Jens Axboe
Browse files

io_uring: limit the number of cancellation buckets 



Don't allocate to many hash/cancellation buckets, there might be too
many, clamp it to 8 bits, or 256 * 64B = 16KB. We don't usually have too
many requests, and 256 buckets should be enough, especially since we
do hash search only in the cancellation path.

Signed-off-by: default avatarPavel Begunkov <asml.silence@gmail.com>
Link: https://lore.kernel.org/r/b9620c8072ba61a2d50eba894b89bd93a94a9abd.1655371007.git.asml.silence@gmail.com


Reviewed-by: default avatarHao Xu <howeyxu@tencent.com>
Signed-off-by: default avatarJens Axboe <axboe@kernel.dk>
parent 4dfab8ab

io_uring/io_uring.c

+5 −5
Original line number Diff line number Diff line
@@ -254,12 +254,12 @@ static __cold struct io_ring_ctx *io_ring_ctx_alloc(struct io_uring_params *p) 


	/*

	 * 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.

	 * 32 entries per hash list if totally full and uniformly spread, but

	 * don't keep too many buckets to not overconsume memory.

	 */

	hash_bits = ilog2(p->cq_entries);

	hash_bits -= 5;

	if (hash_bits <= 0)

		hash_bits = 1;

	hash_bits = ilog2(p->cq_entries) - 5;

	hash_bits = clamp(hash_bits, 1, 8);



	ctx->cancel_hash_bits = hash_bits;

	ctx->cancel_hash =

		kmalloc((1U << hash_bits) * sizeof(struct io_hash_bucket),