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io_uring: limit the number of cancellation buckets

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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: Pavel Begunkov <asml.silence@gmail.com>
Link: https://lore.kernel.org/r/b9620c8072ba61a2d50eba894b89bd93a94a9abd.1655371007.git.asml.silence@gmail.com
Reviewed-by: Hao Xu <howeyxu@tencent.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
This commit is contained in:
Pavel Begunkov 2022-06-16 10:22:05 +01:00 committed by Jens Axboe
parent 4dfab8abb4
commit 4a07723fb4
1 changed files with 5 additions and 5 deletions
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10
io_uring/io_uring.c
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@ -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),