Re: [PATCH] io_uring: Try to merge io requests only for regular files

[Matthew Wilcox]

On Fri, Mar 19, 2021 at 05:28:59AM +, Dmitry Monakhov wrote:
> Otherwise we may endup blocking on pipe or socket.
> 
> Fixes: 6d5d5ac ("io_uring: extend async work merge")

7 bytes of sha1 isn't enough.  You can set core.abbrev to 12 or upgrade
to a version of git from this decade to get that automatically.

> 2.7.4

... is from 2016, so you're five years out of date.  Don't get cut
off when git switches from SHA1.

Re: [PATCH] io_uring: Try to merge io requests only for regular files

[Pavel Begunkov]

On 19/03/2021 05:28, Dmitry Monakhov wrote:
> Otherwise we may endup blocking on pipe or socket.

CC: io-uring ml

> 
> Fixes: 6d5d5ac ("io_uring: extend async work merge")
> Testcase: 
> https://github.com/dmonakhov/liburing/commit/16d171b6ef9d68e6db66650a83d98c5c721d01f6
> Signed-off-by: Dmitry Monakhov 
> ---
>  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;
> +
>   switch (req->submit.opcode) {
>   case IORING_OP_READV:
>   case IORING_OP_READ_FIXED:
> 

-- 
Pavel Begunkov

Re: [PATCH] io_uring: Try to merge io requests only for regular files

[Dmitry Monakhov]

- stable@



19.03.2021, 08:29, "Dmitry Monakhov" :
> 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 
> ---
>  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



From c24cda9aa902775e4e23575b758f009e9fae4640 Mon Sep 17 00:00:00 2001
From: Dmitry Monakhov 
Date: Fri, 19 Mar 2021 08:48:18 +0300
Subject: [PATCH] io_uring: completely disable io_should_merge logic

io_should_merge logic is wierd and prone to latency spikes because of slow neighbors.

Signed-off-by: Dmitry Monakhov 

diff --git a/fs/io_uring.c b/fs/io_uring.c
index 478df7e..a4fb3a7 100644
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -1288,7 +1288,7 @@ static ssize_t io_import_iovec(struct io_ring_ctx *ctx, int rw,
 
 static inline bool io_should_merge(struct async_list *al, struct kiocb *kiocb)
 {
-	if (al->file == kiocb->ki_filp) {
+	if (al->file == kiocb->ki_filp && 0) {
 		off_t start, end;
 
 		/*
-- 
2.7.4

Re: [PATCH] io_uring: Try to merge io requests only for regular files

[Greg KH]

On Fri, Mar 19, 2021 at 05:28:59AM +, Dmitry Monakhov wrote:
> 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 
> ---
>  fs/io_uring.c | 3 +++
>  1 file changed, 3 insertions(+)




This is not the correct way to submit patches for inclusion in the
stable kernel tree.  Please read:
https://www.kernel.org/doc/html/latest/process/stable-kernel-rules.html
for how to do this properly.

[PATCH] io_uring: Try to merge io requests only for regular files

[Dmitry Monakhov]

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 
---
 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;
+
switch (req->submit.opcode) {
case IORING_OP_READV:
case IORING_OP_READ_FIXED:
-- 
2.7.4