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Date:   Tue, 24 Jan 2023 11:50:16 -0800
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Subject: Re: [PATCH v9 6/8] block: Switch to pinning pages.
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To:     David Howells <dhowells@redhat.com>,
        Al Viro <viro@zeniv.linux.org.uk>,
        Christoph Hellwig <hch@infradead.org>
CC:     Matthew Wilcox <willy@infradead.org>, Jens Axboe <axboe@kernel.dk>,
        "Jan Kara" <jack@suse.cz>, Jeff Layton <jlayton@kernel.org>,
        David Hildenbrand <david@redhat.com>,
        Jason Gunthorpe <jgg@nvidia.com>,
        Logan Gunthorpe <logang@deltatee.com>,
        <linux-fsdevel@vger.kernel.org>, <linux-block@vger.kernel.org>,
        <linux-kernel@vger.kernel.org>, "Christoph Hellwig" <hch@lst.de>
References: <20230124170108.1070389-1-dhowells@redhat.com>
 <20230124170108.1070389-7-dhowells@redhat.com>
From:   John Hubbard <jhubbard@nvidia.com>
In-Reply-To: <20230124170108.1070389-7-dhowells@redhat.com>
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On 1/24/23 09:01, David Howells wrote:
> Add BIO_PAGE_PINNED to indicate that the pages in a bio are pinned
> (FOLL_PIN) and that the pin will need removing.
> 
> Signed-off-by: David Howells <dhowells@redhat.com>
> cc: Al Viro <viro@zeniv.linux.org.uk>
> cc: Jens Axboe <axboe@kernel.dk>
> cc: Jan Kara <jack@suse.cz>
> cc: Christoph Hellwig <hch@lst.de>
> cc: Matthew Wilcox <willy@infradead.org>
> cc: Logan Gunthorpe <logang@deltatee.com>
> cc: linux-block@vger.kernel.org
> ---
> 
> Notes:
>      ver #9)
>       - Only consider pinning in bio_set_cleanup_mode().  Ref'ing pages in
>         struct bio is going away.
>       - page_put_unpin() is removed; call unpin_user_page() and put_page()
>         directly.
>       - Use bio_release_page() in __bio_release_pages().
>       - BIO_PAGE_PINNED and BIO_PAGE_REFFED can't both be set, so use if-else
>         when testing both of them.
>      
>      ver #8)
>       - Move the infrastructure to clean up pinned pages to this patch [hch].
>       - Put BIO_PAGE_PINNED before BIO_PAGE_REFFED as the latter should
>         probably be removed at some point.  FOLL_PIN can then be renumbered
>         first.
> 
>   block/bio.c               |  6 +++---
>   block/blk.h               | 21 +++++++++++++++++++++
>   include/linux/bio.h       |  3 ++-
>   include/linux/blk_types.h |  1 +
>   4 files changed, 27 insertions(+), 4 deletions(-)

Neatly avoiding any use of FOLL_PIN or FOLL_GET, good. :)

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

thanks,
-- 
John Hubbard
NVIDIA

> 
> diff --git a/block/bio.c b/block/bio.c
> index 851c23641a0d..fc45aaa97696 100644
> --- a/block/bio.c
> +++ b/block/bio.c
> @@ -1176,7 +1176,7 @@ void __bio_release_pages(struct bio *bio, bool mark_dirty)
>   	bio_for_each_segment_all(bvec, bio, iter_all) {
>   		if (mark_dirty && !PageCompound(bvec->bv_page))
>   			set_page_dirty_lock(bvec->bv_page);
> -		put_page(bvec->bv_page);
> +		bio_release_page(bio, bvec->bv_page);
>   	}
>   }
>   EXPORT_SYMBOL_GPL(__bio_release_pages);
> @@ -1496,8 +1496,8 @@ void bio_set_pages_dirty(struct bio *bio)
>    * the BIO and re-dirty the pages in process context.
>    *
>    * It is expected that bio_check_pages_dirty() will wholly own the BIO from
> - * here on.  It will run one put_page() against each page and will run one
> - * bio_put() against the BIO.
> + * here on.  It will unpin each page and will run one bio_put() against the
> + * BIO.
>    */
>   
>   static void bio_dirty_fn(struct work_struct *work);
> diff --git a/block/blk.h b/block/blk.h
> index 4c3b3325219a..32b252903f9a 100644
> --- a/block/blk.h
> +++ b/block/blk.h
> @@ -425,6 +425,27 @@ int bio_add_hw_page(struct request_queue *q, struct bio *bio,
>   		struct page *page, unsigned int len, unsigned int offset,
>   		unsigned int max_sectors, bool *same_page);
>   
> +/*
> + * Set the cleanup mode for a bio from an iterator and the extraction flags.
> + */
> +static inline void bio_set_cleanup_mode(struct bio *bio, struct iov_iter *iter)
> +{
> +	if (iov_iter_extract_will_pin(iter))
> +		bio_set_flag(bio, BIO_PAGE_PINNED);
> +}
> +
> +/*
> + * Clean up a page appropriately, where the page may be pinned, may have a
> + * ref taken on it or neither.
> + */
> +static inline void bio_release_page(struct bio *bio, struct page *page)
> +{
> +	if (bio_flagged(bio, BIO_PAGE_PINNED))
> +		unpin_user_page(page);
> +	else if (bio_flagged(bio, BIO_PAGE_REFFED))
> +		put_page(page);
> +}
> +
>   struct request_queue *blk_alloc_queue(int node_id);
>   
>   int disk_scan_partitions(struct gendisk *disk, fmode_t mode, void *owner);
> diff --git a/include/linux/bio.h b/include/linux/bio.h
> index 805957c99147..b2c09997d79c 100644
> --- a/include/linux/bio.h
> +++ b/include/linux/bio.h
> @@ -484,7 +484,8 @@ void zero_fill_bio(struct bio *bio);
>   
>   static inline void bio_release_pages(struct bio *bio, bool mark_dirty)
>   {
> -	if (bio_flagged(bio, BIO_PAGE_REFFED))
> +	if (bio_flagged(bio, BIO_PAGE_REFFED) ||
> +	    bio_flagged(bio, BIO_PAGE_PINNED))
>   		__bio_release_pages(bio, mark_dirty);
>   }
>   
> diff --git a/include/linux/blk_types.h b/include/linux/blk_types.h
> index 7daa261f4f98..a0e339ff3d09 100644
> --- a/include/linux/blk_types.h
> +++ b/include/linux/blk_types.h
> @@ -318,6 +318,7 @@ struct bio {
>    * bio flags
>    */
>   enum {
> +	BIO_PAGE_PINNED,	/* Unpin pages in bio_release_pages() */
>   	BIO_PAGE_REFFED,	/* put pages in bio_release_pages() */
>   	BIO_CLONED,		/* doesn't own data */
>   	BIO_BOUNCED,		/* bio is a bounce bio */
>