| Message ID | 20241011132047.1153249-1-hch@lst.de (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | [v3] iov_iter: don't require contiguous pages in iov_iter_extract_bvec_pages | expand |
Btw, this is a missing a: From: Ming Lei <ming.lei@redhat.com> at the top of the mail as it should be credited to Ming of course. On Fri, Oct 11, 2024 at 03:20:22PM +0200, Christoph Hellwig wrote: > 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> > --- > > v3: > - open code the iterator > - improve commit log and comments > > 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 1abb32c0da50bc..9fc06f5fb7489f 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; > } > -- > 2.45.2 > > ---end quoted text---
On Fri, Oct 11, 2024 at 03:20:22PM +0200, Christoph Hellwig wrote: > 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> > --- > > v3: > - open code the iterator > - improve commit log and comments Hello Jens, Gentle ping... thanks, Ming
diff --git a/lib/iov_iter.c b/lib/iov_iter.c index 1abb32c0da50bc..9fc06f5fb7489f 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; }