Re: [PATCH v9 5/8] block: set FOLL_PCI_P2PDMA in __bio_iov_iter_get_pages()

John Hubbard
2022-09-06T00:48:20Z

On 8/25/22 08:24, Logan Gunthorpe wrote:
> When a bio's queue supports PCI P2PDMA, set FOLL_PCI_P2PDMA for
> iov_iter_get_pages_flags(). This allows PCI P2PDMA pages to be passed
> from userspace and enables the O_DIRECT path in iomap based filesystems
> and direct to block devices.

Oh great, more O_DIRECT code paths. :)

>
> Signed-off-by: Logan Gunthorpe <logang@deltatee.com>
> ---
> block/bio.c | 10 ++++++++--
> 1 file changed, 8 insertions(+), 2 deletions(-)
>
> diff --git a/block/bio.c b/block/bio.c
> index 969607bc1f4d..ca09d79a0683 100644
> --- a/block/bio.c
> +++ b/block/bio.c
> @@ -1200,6 +1200,7 @@ static int __bio_iov_iter_get_pages(struct bio *bio, struct iov_iter *iter)
> unsigned short entries_left = bio->bi_max_vecs - bio->bi_vcnt;
> struct bio_vec *bv = bio->bi_io_vec + bio->bi_vcnt;
> struct page **pages = (struct page **)bv;
> + unsigned int flags = 0;

It would be nice to name this gup_flags, instead.

> ssize_t size, left;
> unsigned len, i = 0;
> size_t offset, trim;
> @@ -1213,6 +1214,10 @@ static int __bio_iov_iter_get_pages(struct bio *bio, struct iov_iter *iter)
> BUILD_BUG_ON(PAGE_PTRS_PER_BVEC < 2);
> pages += entries_left * (PAGE_PTRS_PER_BVEC - 1);
>
> + if (bio->bi_bdev && bio->bi_bdev->bd_disk &&
> + blk_queue_pci_p2pdma(bio->bi_bdev->bd_disk->queue))
> + flags |= FOLL_PCI_P2PDMA;
> +
> /*
> * Each segment in the iov is required to be a block size multiple.
> * However, we may not be able to get the entire segment if it spans
> @@ -1220,8 +1225,9 @@ static int __bio_iov_iter_get_pages(struct bio *bio, struct iov_iter *iter)
> * result to ensure the bio's total size is correct. The remainder of
> * the iov data will be picked up in the next bio iteration.
> */
> - size = iov_iter_get_pages2(iter, pages, UINT_MAX - bio->bi_iter.bi_size,
> - nr_pages, &offset);
> + size = iov_iter_get_pages_flags(iter, pages,
> + UINT_MAX - bio->bi_iter.bi_size,
> + nr_pages, &offset, flags);
> if (unlikely(size <= 0))
> return size ? size : -EFAULT;
>

Looks good. After applying Christoph's tweak, and optionally the gup_flags
rename as well, please feel free to add:

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

thanks,

--
John Hubbard
NVIDIA