linux-kernel - Re: [PATCH v9 5/8] block: Replace BIO_NO_PAGE_REF with BIO_PAGE

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Date:   Tue, 24 Jan 2023 11:47:35 -0800
From:   John Hubbard <jhubbard@...dia.com>
To:     David Howells <dhowells@...hat.com>,
        Al Viro <viro@...iv.linux.org.uk>,
        Christoph Hellwig <hch@...radead.org>
CC:     Matthew Wilcox <willy@...radead.org>, Jens Axboe <axboe@...nel.dk>,
        "Jan Kara" <jack@...e.cz>, Jeff Layton <jlayton@...nel.org>,
        David Hildenbrand <david@...hat.com>,
        Jason Gunthorpe <jgg@...dia.com>,
        Logan Gunthorpe <logang@...tatee.com>,
        <linux-fsdevel@...r.kernel.org>, <linux-block@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>, "Christoph Hellwig" <hch@....de>
Subject: Re: [PATCH v9 5/8] block: Replace BIO_NO_PAGE_REF with
 BIO_PAGE_REFFED with inverted logic

On 1/24/23 09:01, David Howells wrote:
> From: Christoph Hellwig <hch@....de>
> 
> Replace BIO_NO_PAGE_REF with a BIO_PAGE_REFFED flag that has the inverted
> meaning is only set when a page reference has been acquired that needs to
> be released by bio_release_pages().
> 
> Signed-off-by: David Howells <dhowells@...hat.com>
> cc: Al Viro <viro@...iv.linux.org.uk>
> cc: Jens Axboe <axboe@...nel.dk>
> cc: Jan Kara <jack@...e.cz>
> cc: Matthew Wilcox <willy@...radead.org>
> cc: Logan Gunthorpe <logang@...tatee.com>
> cc: linux-block@...r.kernel.org
> ---
> 
> Notes:
>      ver #8)
>       - Don't default to BIO_PAGE_REFFED [hch].
>      
>      ver #5)
>       - Split from patch that uses iov_iter_extract_pages().
> 
>   block/bio.c               | 2 +-
>   block/blk-map.c           | 1 +
>   fs/direct-io.c            | 2 ++
>   fs/iomap/direct-io.c      | 1 -
>   include/linux/bio.h       | 2 +-
>   include/linux/blk_types.h | 2 +-
>   6 files changed, 6 insertions(+), 4 deletions(-)

One documentation nit below, but either way,

Reviewed-by: John Hubbard <jhubbard@...dia.com>

> 
> diff --git a/block/bio.c b/block/bio.c
> index 683444e6b711..851c23641a0d 100644
> --- a/block/bio.c
> +++ b/block/bio.c
> @@ -1198,7 +1198,6 @@ void bio_iov_bvec_set(struct bio *bio, struct iov_iter *iter)
>   	bio->bi_io_vec = (struct bio_vec *)iter->bvec;
>   	bio->bi_iter.bi_bvec_done = iter->iov_offset;
>   	bio->bi_iter.bi_size = size;
> -	bio_set_flag(bio, BIO_NO_PAGE_REF);
>   	bio_set_flag(bio, BIO_CLONED);
>   }
>   
> @@ -1343,6 +1342,7 @@ int bio_iov_iter_get_pages(struct bio *bio, struct iov_iter *iter)
>   		return 0;
>   	}
>   
> +	bio_set_flag(bio, BIO_PAGE_REFFED);
>   	do {
>   		ret = __bio_iov_iter_get_pages(bio, iter);
>   	} while (!ret && iov_iter_count(iter) && !bio_full(bio, 0));
> diff --git a/block/blk-map.c b/block/blk-map.c
> index 7db52ad5b2d0..0e2b0a861ba3 100644
> --- a/block/blk-map.c
> +++ b/block/blk-map.c
> @@ -282,6 +282,7 @@ static int bio_map_user_iov(struct request *rq, struct iov_iter *iter,
>   	if (blk_queue_pci_p2pdma(rq->q))
>   		extraction_flags |= ITER_ALLOW_P2PDMA;
>   
> +	bio_set_flag(bio, BIO_PAGE_REFFED);
>   	while (iov_iter_count(iter)) {
>   		struct page **pages, *stack_pages[UIO_FASTIOV];
>   		ssize_t bytes;
> diff --git a/fs/direct-io.c b/fs/direct-io.c
> index 03d381377ae1..07810465fc9d 100644
> --- a/fs/direct-io.c
> +++ b/fs/direct-io.c
> @@ -403,6 +403,8 @@ dio_bio_alloc(struct dio *dio, struct dio_submit *sdio,
>   		bio->bi_end_io = dio_bio_end_aio;
>   	else
>   		bio->bi_end_io = dio_bio_end_io;
> +	/* for now require references for all pages */

Maybe just delete this comment?

thanks,
-- 
John Hubbard
NVIDIA