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

[Christoph Hellwig <hch@infradead.org>]

On Mon, Nov 19, 2018 at 12:51:31PM +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>

Looks good,

Reviewed-by: Christoph Hellwig <hch@lst.de>