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block: use bio_add_page in bio_iov_iter_get_pages 

Replace a nasty hack with a different nasty hack to prepare for multipage
bio_vecs.  By moving the temporary page array as far up as possible in
the space allocated for the bio_vec array we can iterate forward over it
and thus use bio_add_page.  Using bio_add_page means we'll be able to
merge physically contiguous pages once support for multipath bio_vecs is
merged.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
This commit is contained in:
Christoph Hellwig 2018-09-20 08:28:21 +02:00 committed by Jens Axboe
parent c8765de0ad
commit 576ed91354
1 changed files with 20 additions and 21 deletions
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41
block/bio.c
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@ -827,6 +827,8 @@ int bio_add_page(struct bio *bio, struct page *page,
}
EXPORT_SYMBOL(bio_add_page);
#define PAGE_PTRS_PER_BVEC (sizeof(struct bio_vec) / sizeof(struct page *))
/**
* __bio_iov_iter_get_pages - pin user or kernel pages and add them to a bio
* @bio: bio to add pages to
@ -839,38 +841,35 @@ EXPORT_SYMBOL(bio_add_page);
*/
static int __bio_iov_iter_get_pages(struct bio *bio, struct iov_iter *iter)
{
unsigned short nr_pages = bio->bi_max_vecs - bio->bi_vcnt, idx;
unsigned short nr_pages = bio->bi_max_vecs - bio->bi_vcnt;
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;
ssize_t size, left;
unsigned len, i;
size_t offset;
ssize_t size;
/*
* Move page array up in the allocated memory for the bio vecs as far as
* possible so that we can start filling biovecs from the beginning
* without overwriting the temporary page array.
*/
BUILD_BUG_ON(PAGE_PTRS_PER_BVEC < 2);
pages += entries_left * (PAGE_PTRS_PER_BVEC - 1);
size = iov_iter_get_pages(iter, pages, LONG_MAX, nr_pages, &offset);
if (unlikely(size <= 0))
return size ? size : -EFAULT;
idx = nr_pages = (size + offset + PAGE_SIZE - 1) / PAGE_SIZE;
/*
* Deep magic below: We need to walk the pinned pages backwards
* because we are abusing the space allocated for the bio_vecs
* for the page array. Because the bio_vecs are larger than the
* page pointers by definition this will always work. But it also
* means we can't use bio_add_page, so any changes to it's semantics
* need to be reflected here as well.
*/
bio->bi_iter.bi_size += size;
bio->bi_vcnt += nr_pages;
for (left = size, i = 0; left > 0; left -= len, i++) {
struct page *page = pages[i];
while (idx--) {
bv[idx].bv_page = pages[idx];
bv[idx].bv_len = PAGE_SIZE;
bv[idx].bv_offset = 0;
len = min_t(size_t, PAGE_SIZE - offset, left);
if (WARN_ON_ONCE(bio_add_page(bio, page, len, offset) != len))
return -EINVAL;
offset = 0;
}
bv[0].bv_offset += offset;
bv[0].bv_len -= offset;
bv[nr_pages - 1].bv_len -= nr_pages * PAGE_SIZE - offset - size;
iov_iter_advance(iter, size);
return 0;
}