linux-kernel - Re: [PATCH v2] io-wq: expose IO_WQ_ACCT

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Date:   Mon, 13 Sep 2021 07:28:11 -0600
From:   Jens Axboe <axboe@...nel.dk>
To:     Eugene Syromiatnikov <esyr@...hat.com>,
        Pavel Begunkov <asml.silence@...il.com>
Cc:     io-uring@...r.kernel.org, linux-kernel@...r.kernel.org,
        "Dmitry V. Levin" <ldv@...ace.io>, linux-api@...r.kernel.org
Subject: Re: [PATCH v2] io-wq: expose IO_WQ_ACCT_* enumeration items to UAPI

On 9/13/21 4:41 AM, Eugene Syromiatnikov wrote:
> These are used to index elements in the argument
> of IORING_REGISTER_IOWQ_MAX_WORKERS io_uring_register command,
> so they are to be exposed in UAPI.
> 
> Complements: 2e480058ddc21ec5 ("io-wq: provide a way to limit max number of workers")
> Signed-off-by: Eugene Syromiatnikov <esyr@...hat.com>
> ---
> v2:
>  - IO_WQ_ACCT_NR is no longer exposed directly in UAPI, per Jens Axboe's
>    suggestion.
> 
> v1: https://lore.kernel.org/lkml/20210912122411.GA27679@asgard.redhat.com/
> ---
>  fs/io-wq.c                    | 5 ++---
>  include/uapi/linux/io_uring.h | 8 ++++++++
>  2 files changed, 10 insertions(+), 3 deletions(-)
> 
> diff --git a/fs/io-wq.c b/fs/io-wq.c
> index 6c55362..eb5162d 100644
> --- a/fs/io-wq.c
> +++ b/fs/io-wq.c
> @@ -14,6 +14,7 @@
>  #include <linux/rculist_nulls.h>
>  #include <linux/cpu.h>
>  #include <linux/tracehook.h>
> +#include <uapi/linux/io_uring.h>
>  
>  #include "io-wq.h"
>  
> @@ -78,9 +79,7 @@ struct io_wqe_acct {
>  };
>  
>  enum {
> -	IO_WQ_ACCT_BOUND,
> -	IO_WQ_ACCT_UNBOUND,
> -	IO_WQ_ACCT_NR,
> +	IO_WQ_ACCT_NR = __IO_WQ_ACCT_MAX
>  };
>  
>  /*
> diff --git a/include/uapi/linux/io_uring.h b/include/uapi/linux/io_uring.h
> index 59ef351..dae1841 100644
> --- a/include/uapi/linux/io_uring.h
> +++ b/include/uapi/linux/io_uring.h
> @@ -324,6 +324,14 @@ enum {
>  	IORING_REGISTER_LAST
>  };
>  
> +/* io-wq worker limit categories */
> +enum {
> +	IO_WQ_ACCT_BOUND,
> +	IO_WQ_ACCT_UNBOUND,
> +
> +	__IO_WQ_ACCT_MAX /* Non-UAPI */
> +};

This is really the same thing as before, just the names have changed.
What I suggested was keeping the enum in io_uring, then just adding

enum {
	IO_WQ_BOUND,
	IO_WQ_UNBOUND,
};

to uapi header. The ACCT stuff is io-wq specific too, that kind of naming
shouldn't be propagated to userspace.

A BUILD_BUG_ON() could be added for them being different, but honestly
I don't think that's worth it.

-- 
Jens Axboe