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SubjectRe: [PATCH 10/17] bio: use bio_create_from_sgl() in bio_map_user_iov()
On 04/01/2009 04:44 PM, Tejun Heo wrote:
> Impact: cleanup
>
> As bio_map_user_iov() is unique in the way it acquires pages to map
> from all other three operations (user-copy, kern-map, kern-copy), the
> function still needs to get the pages itself but the bio creation can
> use bio_create_from_sgl(). Create sgl of mapped pages and use it to
> create bio from it. The code will be further simplified with future
> changes to bio_create_from_sgl().
>
> Signed-off-by: Tejun Heo <tj@kernel.org>
> ---
> fs/bio.c | 79 ++++++++++++++++++++++++++------------------------------------
> 1 files changed, 33 insertions(+), 46 deletions(-)
>
> diff --git a/fs/bio.c b/fs/bio.c
> index 4540afc..1ca8b16 100644
> --- a/fs/bio.c
> +++ b/fs/bio.c
> @@ -1059,13 +1059,13 @@ struct bio *bio_copy_user(struct request_queue *q, struct rq_map_data *md,
> struct bio *bio_map_user_iov(struct request_queue *q, struct block_device *bdev,
> struct iovec *iov, int count, int rw, gfp_t gfp)
> {
> - int i, j;
> size_t tot_len = 0;
> int nr_pages = 0;
> + int nents = 0;
> + struct scatterlist *sgl;
> struct page **pages;
> struct bio *bio;
> - int cur_page = 0;
> - int ret, offset;
> + int i, ret;
>
> for (i = 0; i < count; i++) {
> unsigned long uaddr = (unsigned long)iov[i].iov_base;
> @@ -1088,70 +1088,57 @@ struct bio *bio_map_user_iov(struct request_queue *q, struct block_device *bdev,
> if (!nr_pages || tot_len & q->dma_pad_mask)
> return ERR_PTR(-EINVAL);
>
> - bio = bio_kmalloc(gfp, nr_pages);
> - if (!bio)
> + sgl = kmalloc(nr_pages * sizeof(sgl[0]), gfp);
> + if (!sgl)
> return ERR_PTR(-ENOMEM);
> + sg_init_table(sgl, nr_pages);
>
> ret = -ENOMEM;
> - pages = kcalloc(nr_pages, sizeof(struct page *), gfp);
> + pages = kcalloc(nr_pages, sizeof(pages[0]), gfp);
> if (!pages)
> - goto out;
> + goto err_sgl;
>
> for (i = 0; i < count; i++) {
> unsigned long uaddr = (unsigned long)iov[i].iov_base;
> unsigned long len = iov[i].iov_len;
> - unsigned long end = (uaddr + len + PAGE_SIZE - 1) >> PAGE_SHIFT;
> - unsigned long start = uaddr >> PAGE_SHIFT;
> - const int local_nr_pages = end - start;
> - const int page_limit = cur_page + local_nr_pages;
> -
> + unsigned long offset = offset_in_page(uaddr);
> + int local_nr_pages = PFN_UP(uaddr + len) - PFN_DOWN(uaddr);
> +
> ret = get_user_pages_fast(uaddr, local_nr_pages, rw == READ,
> - &pages[cur_page]);
> + &pages[nents]);

Fast look at all users of get_user_pages_fast().

This can be converted to take an sglist instead of pages* array.
Outside of this code all users either have a fixed-size allocated array
or hard coded one page. This here is the main user. (Out of 5)

Note to self:

> if (ret < local_nr_pages) {
> ret = -EFAULT;
> - goto out_unmap;
> + goto err_pages;
> }
>
> - offset = uaddr & ~PAGE_MASK;
> - for (j = cur_page; j < page_limit; j++) {
> - unsigned int bytes = PAGE_SIZE - offset;
> + while (len) {
> + unsigned int bytes = min(PAGE_SIZE - offset, len);
>
> - if (len <= 0)
> - break;
> -
> - if (bytes > len)
> - bytes = len;
> -
> - /*
> - * sorry...
> - */
> - if (bio_add_pc_page(q, bio, pages[j], bytes, offset) <
> - bytes)
> - break;
> + sg_set_page(&sgl[nents], pages[nents], bytes, offset);
>
> + nents++;
> len -= bytes;
> offset = 0;
> }
> -
> - cur_page = j;
> - /*
> - * release the pages we didn't map into the bio, if any
> - */
> - while (j < page_limit)
> - page_cache_release(pages[j++]);
> }
> + BUG_ON(nents != nr_pages);
>
> - kfree(pages);
> + bio = bio_create_from_sgl(q, sgl, nents, nr_pages, rw, gfp);
> + if (IS_ERR(bio)) {
> + ret = PTR_ERR(bio);
> + goto err_pages;
> + }
>
> - /*
> - * set data direction, and check if mapped pages need bouncing
> - */
> - if (rw == WRITE)
> - bio->bi_rw |= (1 << BIO_RW);
> + /* release the pages we didn't map into the bio, if any */
> + for (i = bio->bi_vcnt; i < nr_pages; i++)
> + page_cache_release(pages[i]);
>
> bio->bi_bdev = bdev;
> bio->bi_flags |= (1 << BIO_USER_MAPPED);
>
> + kfree(sgl);
> + kfree(pages);
> +
> /*
> * subtle -- if __bio_map_user() ended up bouncing a bio,
> * it would normally disappear when its bi_end_io is run.
> @@ -1162,15 +1149,15 @@ struct bio *bio_map_user_iov(struct request_queue *q, struct block_device *bdev,
>
> return bio;
>
> - out_unmap:
> +err_pages:
> for (i = 0; i < nr_pages; i++) {
> - if(!pages[i])
> + if (!pages[i])
> break;
> page_cache_release(pages[i]);
> }
> - out:
> kfree(pages);
> - bio_put(bio);
> +err_sgl:
> + kfree(sgl);
> return ERR_PTR(ret);
> }
>



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