Re: [PATCH 7/7] block: Initialize BIO I/O priority early

From: Adam Manzanares <Adam.Manzanares@wdc.com>
To: "linux-block@vger.kernel.org" <linux-block@vger.kernel.org>,
	Damien Le Moal <Damien.LeMoal@wdc.com>,
	"axboe@kernel.dk" <axboe@kernel.dk>
Cc: "viro@zeniv.linux.org.uk" <viro@zeniv.linux.org.uk>,
	"linux-fsdevel@vger.kernel.org" <linux-fsdevel@vger.kernel.org>
Subject: Re: [PATCH 7/7] block: Initialize BIO I/O priority early
Date: Mon, 19 Nov 2018 19:11:53 +0000	[thread overview]
Message-ID: <d0ea8395e43bd634a9001d9cf96bc807cdb688d7.camel@wdc.com> (raw)
In-Reply-To: <20181119035131.11255-8-damien.lemoal@wdc.com>

On Mon, 2018-11-19 at 12:51 +0900, Damien Le Moal wrote:
> For the synchronous I/O path case (read(), write() etc system calls),
> a
> BIO I/O priority is not initialized until the execution of
> blk_init_request_from_bio() when the BIO is submitted and a request
> initialized for the BIO execution. This is due to the ki_ioprio field
> of
> the struct kiocb defined on stack being always initialized to
> IOPRIO_CLASS_NONE, regardless of the calling process I/O context
> ioprio
> value set with ioprio_set(). This late initialization can result in
> the
> BIO being merged to pending requests even when the I/O priorities
> differ.
> 
> Fix this by initializing the ki_iopriority field of on stack struct
> kiocb using the get_current_ioprio() helper, ensuring that all BIOs
> allocated and submitted for the system call execution see the correct
> intended I/O priority early. With this, since a BIO I/O priority is
> always set to the intended effective value for both the sync and
> async
> path, blk_init_request_from_bio() can be simplified.
> 
> Signed-off-by: Damien Le Moal <damien.lemoal@wdc.com>

Nice cleanup, looks good. Thanks Damien.

Reviewed-by: Adam Manzanares <adam.manzanares@wdc.com>

> ---
>  block/blk-core.c   | 5 +----
>  include/linux/fs.h | 2 +-
>  2 files changed, 2 insertions(+), 5 deletions(-)
> 
> diff --git a/block/blk-core.c b/block/blk-core.c
> index dde30b08aa14..04f5be473638 100644
> --- a/block/blk-core.c
> +++ b/block/blk-core.c
> @@ -814,10 +814,7 @@ void blk_init_request_from_bio(struct request
> *req, struct bio *bio)
>  		req->cmd_flags |= REQ_FAILFAST_MASK;
>  
>  	req->__sector = bio->bi_iter.bi_sector;
> -	if (ioprio_valid(bio_prio(bio)))
> -		req->ioprio = bio_prio(bio);
> -	else
> -		req->ioprio = get_current_ioprio();
> +	req->ioprio = bio_prio(bio);
>  	req->write_hint = bio->bi_write_hint;
>  	blk_rq_bio_prep(req->q, req, bio);
>  }
> diff --git a/include/linux/fs.h b/include/linux/fs.h
> index c95c0807471f..a1ab233e6469 100644
> --- a/include/linux/fs.h
> +++ b/include/linux/fs.h
> @@ -2021,7 +2021,7 @@ static inline void init_sync_kiocb(struct kiocb
> *kiocb, struct file *filp)
>  		.ki_filp = filp,
>  		.ki_flags = iocb_flags(filp),
>  		.ki_hint = ki_hint_validate(file_write_hint(filp)),
> -		.ki_ioprio = IOPRIO_PRIO_VALUE(IOPRIO_CLASS_NONE, 0),
> +		.ki_ioprio = get_current_ioprio(),
>  	};
>  }
>  