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Message-Id: <61611616138730@mail.yandex-team.ru>
Date: Fri, 19 Mar 2021 10:45:46 +0300
From: Dmitry Monakhov <dmtrmonakhov@...dex-team.ru>
To: "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Cc: "linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>,
"axboe@...nel.dk" <axboe@...nel.dk>
Subject: Re: [PATCH] io_uring: Try to merge io requests only for regular files
- stable@
19.03.2021, 08:29, "Dmitry Monakhov" <dmtrmonakhov@...dex-team.ru>:
> Otherwise we may endup blocking on pipe or socket.
>
> Fixes: 6d5d5ac ("io_uring: extend async work merge")
> Testcase: https://github.com/dmonakhov/liburing/commit/16d171b6ef9d68e6db66650a83d98c5c721d01f6
> Signed-off-by: Dmitry Monakhov <dmtrmonakhov@...dex-team.ru>
> ---
> fs/io_uring.c | 3 +++
> 1 file changed, 3 insertions(+)
>
> diff --git a/fs/io_uring.c b/fs/io_uring.c
> index 478df7e..848657c 100644
> --- a/fs/io_uring.c
> +++ b/fs/io_uring.c
> @@ -2183,6 +2183,9 @@ static int __io_submit_sqe(struct io_ring_ctx *ctx, struct io_kiocb *req,
> static struct async_list *io_async_list_from_req(struct io_ring_ctx *ctx,
> struct io_kiocb *req)
> {
> + if (!(req->flags & REQ_F_ISREG))
> + return NULL;
> +
IMHO it is reasonable to completely disable io_should_merge logic because
even with the this fix it still affected by latency spikes like follows:
->submit_read: req1[slow_hdd, sector=z]
->submit_read: req2[nvme, sector=X]
-> wait(req2) -> fast
->submit_read: req3[nvme, sector=Y]
--> wait(req3) ->slow
if completes if X and Y belongs to same page merge logic will wait for req1 to complete
View attachment "0001-io_uring-completely-disable-io_should_merge-logic.patch" of type "text/x-diff" (780 bytes)
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