Re: [PATCH] iov_iter: don't require contiguous pages in iov_iter_extract_bvec_pages

Klara Modin
2024-10-30T17:56:54Z

[-- Attachment #1: Type: text/plain, Size: 4240 bytes --]

Hi,

On 2024-10-24 07:00, Christoph Hellwig wrote:
> From: Ming Lei <ming.lei@redhat.com>
>
> The iov_iter_extract_pages interface allows to return physically
> discontiguous pages, as long as all but the first and last page
> in the array are page aligned and page size. Rewrite
> iov_iter_extract_bvec_pages to take advantage of that instead of only
> returning ranges of physically contiguous pages.
>
> Signed-off-by: Ming Lei <ming.lei@redhat.com>
> [hch: minor cleanups, new commit log]
> Signed-off-by: Christoph Hellwig <hch@lst.de>

With this patch (e4e535bff2bc82bb49a633775f9834beeaa527db in
next-20241030), I'm unable to connect via nvme-tcp with this in the log:

nvme nvme1: failed to send request -5
nvme nvme1: Connect command failed: host path error
nvme nvme1: failed to connect queue: 0 ret=880

With the patch reverted it works as expected:

nvme nvme1: creating 24 I/O queues.
nvme nvme1: mapped 24/0/0 default/read/poll queues.
nvme nvme1: new ctrl: NQN
"nqn.2018-06.eu.kasm.int:freenas:backup:parmesan.int.kasm.eu", addr
[2001:0678:0a5c:1204:6245:cbff:fe9c:4f59]:4420, hostnqn:
nqn.2018-06.eu.kasm.int:parmesan

Please let me know if there's anything else you need.

Regards,
Klara Modin

+CC: linux-nvme

> ---
> lib/iov_iter.c | 67 +++++++++++++++++++++++++++++++++-----------------
> 1 file changed, 45 insertions(+), 22 deletions(-)
>
> diff --git a/lib/iov_iter.c b/lib/iov_iter.c
> index 1abb32c0da50..9fc06f5fb748 100644
> --- a/lib/iov_iter.c
> +++ b/lib/iov_iter.c
> @@ -1677,8 +1677,8 @@ static ssize_t iov_iter_extract_xarray_pages(struct iov_iter *i,
> }
>
> /*
> - * Extract a list of contiguous pages from an ITER_BVEC iterator. This does
> - * not get references on the pages, nor does it get a pin on them.
> + * Extract a list of virtually contiguous pages from an ITER_BVEC iterator.
> + * This does not get references on the pages, nor does it get a pin on them.
> */
> static ssize_t iov_iter_extract_bvec_pages(struct iov_iter *i,
> struct page ***pages, size_t maxsize,
> @@ -1686,35 +1686,58 @@ static ssize_t iov_iter_extract_bvec_pages(struct iov_iter *i,
> iov_iter_extraction_t extraction_flags,
> size_t *offset0)
> {
> - struct page **p, *page;
> - size_t skip = i->iov_offset, offset, size;
> - int k;
> + size_t skip = i->iov_offset, size = 0;
> + struct bvec_iter bi;
> + int k = 0;
>
> - for (;;) {
> - if (i->nr_segs == 0)
> - return 0;
> - size = min(maxsize, i->bvec->bv_len - skip);
> - if (size)
> - break;
> + if (i->nr_segs == 0)
> + return 0;
> +
> + if (i->iov_offset == i->bvec->bv_len) {
> i->iov_offset = 0;
> i->nr_segs--;
> i->bvec++;
> skip = 0;
> }
> + bi.bi_size = maxsize + skip;
> + bi.bi_bvec_done = skip;
> +
> + maxpages = want_pages_array(pages, maxsize, skip, maxpages);
> +
> + while (bi.bi_size && bi.bi_idx < i->nr_segs) {
> + struct bio_vec bv = bvec_iter_bvec(i->bvec, bi);
> +
> + /*
> + * The iov_iter_extract_pages interface only allows an offset
> + * into the first page. Break out of the loop if we see an
> + * offset into subsequent pages, the caller will have to call
> + * iov_iter_extract_pages again for the reminder.
> + */
> + if (k) {
> + if (bv.bv_offset)
> + break;
> + } else {
> + *offset0 = bv.bv_offset;
> + }
>
> - skip += i->bvec->bv_offset;
> - page = i->bvec->bv_page + skip / PAGE_SIZE;
> - offset = skip % PAGE_SIZE;
> - *offset0 = offset;
> + (*pages)[k++] = bv.bv_page;
> + size += bv.bv_len;
>
> - maxpages = want_pages_array(pages, size, offset, maxpages);
> - if (!maxpages)
> - return -ENOMEM;
> - p = *pages;
> - for (k = 0; k < maxpages; k++)
> - p[k] = page + k;
> + if (k >= maxpages)
> + break;
> +
> + /*
> + * We are done when the end of the bvec doesn't align to a page
> + * boundary as that would create a hole in the returned space.
> + * The caller will handle this with another call to
> + * iov_iter_extract_pages.
> + */
> + if (bv.bv_offset + bv.bv_len != PAGE_SIZE)
> + break;
> +
> + bvec_iter_advance_single(i->bvec, &bi, bv.bv_len);
> + }
>
> - size = min_t(size_t, size, maxpages * PAGE_SIZE - offset);
> iov_iter_advance(i, size);
> return size;
> }

[-- Attachment #2: config.gz --]
[-- Type: application/gzip, Size: 46058 bytes --]

[-- Attachment #3: nvme-tcp_host-path-error_bisect --]
[-- Type: text/plain, Size: 2769 bytes --]

# bad: [cadd411a755d40bf717c2514afb90c7c0762aefc] crypto: rsassa-pkcs1 - Migrate to sig_alg backend
# good: [e42b1a9a2557aa94fee47f078633677198386a52] Merge tag 'spi-fix-v6.12-rc5' of git://git.kernel.org/pub/scm/linux/kernel/git/broonie/spi
git bisect start 'next' 'next/stable'
# good: [5837b9daa339313b9009011e0173dd874de3f132] Merge branch 'spi-nor/next' of git://git.kernel.org/pub/scm/linux/kernel/git/mtd/linux.git
git bisect good 5837b9daa339313b9009011e0173dd874de3f132
# bad: [64f1d5c3ad7542ea8f979988d2af75fd4e18148e] Merge branch 'for-backlight-next' of git://git.kernel.org/pub/scm/linux/kernel/git/lee/backlight.git
git bisect bad 64f1d5c3ad7542ea8f979988d2af75fd4e18148e
# good: [e7103f8785504dd5c6aad118fbc64fc49eda33af] Merge tag 'amd-drm-next-6.13-2024-10-25' of https://gitlab.freedesktop.org/agd5f/linux into drm-next
git bisect good e7103f8785504dd5c6aad118fbc64fc49eda33af
# good: [7487abf914ecae6ad2690493c2a3fb998738bd71] Merge branch 'for-next' of https://git.kernel.org/pub/scm/linux/kernel/git/ieee1394/linux1394.git
git bisect good 7487abf914ecae6ad2690493c2a3fb998738bd71
# good: [3f743e703c251c9c3f22088bcdc0330e165c8c94] Merge branch 'next' of git://git.kernel.org/pub/scm/linux/kernel/git/dtor/input.git
git bisect good 3f743e703c251c9c3f22088bcdc0330e165c8c94
# bad: [9401ff8e2d60f43ecf343c20a7595b2711bce217] Merge branch 'for-next' of git://git.kernel.org/pub/scm/linux/kernel/git/libata/linux
git bisect bad 9401ff8e2d60f43ecf343c20a7595b2711bce217
# good: [aff750e7094e26eae686965930ef2bec7f4152da] io_uring/rsrc: clear ->buf before mapping pages
git bisect good aff750e7094e26eae686965930ef2bec7f4152da
# good: [904ebd2527c507752f5ddb358f887d2e0dab96a0] block: remove redundant explicit memory barrier from rq_qos waiter and waker
git bisect good 904ebd2527c507752f5ddb358f887d2e0dab96a0
# bad: [d49acf07fd5629a7e96d3f6cb4a28f5cc04a10bf] Merge branch 'for-next' of git://git.kernel.dk/linux-block.git
git bisect bad d49acf07fd5629a7e96d3f6cb4a28f5cc04a10bf
# good: [f1be1788a32e8fa63416ad4518bbd1a85a825c9d] block: model freeze & enter queue as lock for supporting lockdep
git bisect good f1be1788a32e8fa63416ad4518bbd1a85a825c9d
# bad: [793c08dfe78b646031fe2aa5910e6fef6e872e4a] Merge branch 'for-6.13/block' into for-next
git bisect bad 793c08dfe78b646031fe2aa5910e6fef6e872e4a
# bad: [2f5a65ef30a636d5030917eebd283ac447a212af] block: add a bdev_limits helper
git bisect bad 2f5a65ef30a636d5030917eebd283ac447a212af
# bad: [e4e535bff2bc82bb49a633775f9834beeaa527db] iov_iter: don't require contiguous pages in iov_iter_extract_bvec_pages
git bisect bad e4e535bff2bc82bb49a633775f9834beeaa527db
# first bad commit: [e4e535bff2bc82bb49a633775f9834beeaa527db] iov_iter: don't require contiguous pages in iov_iter_extract_bvec_pages