On Wed, Mar 05, 2025 at 07:05:27AM -0700, Christoph Hellwig wrote:
> The fallback buffer allocation path currently open codes a suboptimal
> version of vmalloc to allocate pages that are then mapped into
> vmalloc space. Switch to using vmalloc instead, which uses all the
> optimizations in the common vmalloc code, and removes the need to
> track the backing pages in the xfs_buf structure.
>
> Signed-off-by: Christoph Hellwig <hch@xxxxxx>
.....
> @@ -1500,29 +1373,43 @@ static void
> xfs_buf_submit_bio(
> struct xfs_buf *bp)
> {
> - unsigned int size = BBTOB(bp->b_length);
> - unsigned int map = 0, p;
> + unsigned int map = 0;
> struct blk_plug plug;
> struct bio *bio;
>
> - bio = bio_alloc(bp->b_target->bt_bdev, bp->b_page_count,
> - xfs_buf_bio_op(bp), GFP_NOIO);
> - bio->bi_private = bp;
> - bio->bi_end_io = xfs_buf_bio_end_io;
> + if (is_vmalloc_addr(bp->b_addr)) {
> + unsigned int size = BBTOB(bp->b_length);
> + unsigned int alloc_size = roundup(size, PAGE_SIZE);
> + void *data = bp->b_addr;
>
> - if (bp->b_page_count == 1) {
> - __bio_add_page(bio, virt_to_page(bp->b_addr), size,
> - offset_in_page(bp->b_addr));
> - } else {
> - for (p = 0; p < bp->b_page_count; p++)
> - __bio_add_page(bio, bp->b_pages[p], PAGE_SIZE, 0);
> - bio->bi_iter.bi_size = size; /* limit to the actual size used */
> + bio = bio_alloc(bp->b_target->bt_bdev, alloc_size >> PAGE_SHIFT,
> + xfs_buf_bio_op(bp), GFP_NOIO);
> +
> + do {
> + unsigned int len = min(size, PAGE_SIZE);
>
> - if (is_vmalloc_addr(bp->b_addr))
> - flush_kernel_vmap_range(bp->b_addr,
> - xfs_buf_vmap_len(bp));
> + ASSERT(offset_in_page(data) == 0);
> + __bio_add_page(bio, vmalloc_to_page(data), len, 0);
> + data += len;
> + size -= len;
> + } while (size);
> +
> + flush_kernel_vmap_range(bp->b_addr, alloc_size);
> + } else {
> + /*
> + * Single folio or slab allocation. Must be contiguous and thus
> + * only a single bvec is needed.
> + */
> + bio = bio_alloc(bp->b_target->bt_bdev, 1, xfs_buf_bio_op(bp),
> + GFP_NOIO);
> + __bio_add_page(bio, virt_to_page(bp->b_addr),
> + BBTOB(bp->b_length),
> + offset_in_page(bp->b_addr));
> }
How does offset_in_page() work with a high order folio? It can only
return a value between 0 and (PAGE_SIZE - 1). i.e. shouldn't this
be:
folio = kmem_to_folio(bp->b_addr);
bio_add_folio_nofail(bio, folio, BBTOB(bp->b_length),
offset_in_folio(folio, bp->b_addr));
-Dave.
--
Dave Chinner
david@xxxxxxxxxxxxx
