linux-kernel - Re: [PATCH v8 07/10] block: Switch to pinning pages.

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Message-ID: <2431ffa0-4a37-56a2-17fa-74a5f681bcb8@redhat.com>
Date:   Tue, 24 Jan 2023 15:32:18 +0100
From:   David Hildenbrand <david@...hat.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>,
        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 v8 07/10] block: Switch to pinning pages.

On 23.01.23 18:30, 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@...hat.com>
> cc: Al Viro <viro@...iv.linux.org.uk>
> cc: Jens Axboe <axboe@...nel.dk>
> cc: Jan Kara <jack@...e.cz>
> cc: Christoph Hellwig <hch@....de>
> cc: Matthew Wilcox <willy@...radead.org>
> cc: Logan Gunthorpe <logang@...tatee.com>
> cc: linux-block@...r.kernel.org
> ---
> 
> Notes:
>      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               |  7 ++++---
>   block/blk.h               | 28 ++++++++++++++++++++++++++++
>   include/linux/bio.h       |  3 ++-
>   include/linux/blk_types.h |  1 +
>   4 files changed, 35 insertions(+), 4 deletions(-)
> 
> diff --git a/block/bio.c b/block/bio.c
> index 40c2b01906da..6f98bcfc0c92 100644
> --- a/block/bio.c
> +++ b/block/bio.c
> @@ -1170,13 +1170,14 @@ bool bio_add_folio(struct bio *bio, struct folio *folio, size_t len,
>   
>   void __bio_release_pages(struct bio *bio, bool mark_dirty)
>   {
> +	unsigned int gup_flags = bio_to_gup_flags(bio);
>   	struct bvec_iter_all iter_all;
>   	struct bio_vec *bvec;
>   
>   	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);
> +		page_put_unpin(bvec->bv_page, gup_flags);
>   	}
>   }
>   EXPORT_SYMBOL_GPL(__bio_release_pages);
> @@ -1496,8 +1497,8 @@ 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 run one page_put_unpin() against 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..294044d696e0 100644
> --- a/block/blk.h
> +++ b/block/blk.h
> @@ -425,6 +425,34 @@ 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)
> +{
> +	unsigned int cleanup_mode = iov_iter_extract_mode(iter);
> +
> +	if (cleanup_mode & FOLL_GET)
> +		bio_set_flag(bio, BIO_PAGE_REFFED);
> +	if (cleanup_mode & FOLL_PIN)
> +		bio_set_flag(bio, BIO_PAGE_PINNED);

Can FOLL_GET ever happen?

IOW, can't this even be

if (user_backed_iter(iter))
	bio_set_flag(bio, BIO_PAGE_PINNED);

-- 
Thanks,

David / dhildenb