Re: [PATCH] iov_iter: don't require contiguous pages in iov_iter_extract_bvec_pages
From: Klara Modin
Date: Wed Oct 30 2024 - 13:57:06 EST
Hi,
On 2024-10-24 07:00, Christoph Hellwig wrote:
From: Ming Lei <ming.lei@xxxxxxxxxx>
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@xxxxxxxxxx>
[hch: minor cleanups, new commit log]
Signed-off-by: Christoph Hellwig <hch@xxxxxx>
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;
}
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# 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
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git bisect bad 64f1d5c3ad7542ea8f979988d2af75fd4e18148e
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# good: [904ebd2527c507752f5ddb358f887d2e0dab96a0] block: remove redundant explicit memory barrier from rq_qos waiter and waker
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# bad: [d49acf07fd5629a7e96d3f6cb4a28f5cc04a10bf] Merge branch 'for-next' of git://git.kernel.dk/linux-block.git
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# bad: [793c08dfe78b646031fe2aa5910e6fef6e872e4a] Merge branch 'for-6.13/block' into for-next
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# bad: [2f5a65ef30a636d5030917eebd283ac447a212af] block: add a bdev_limits helper
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# 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