On Wed, May 19, 2021 at 11:07:33AM +1000, Dave Chinner wrote:
> From: Dave Chinner <dchinner@xxxxxxxxxx>
>
> Because it's more efficient than allocating pages one at a time in a
> loop.
>
> Signed-off-by: Dave Chinner <dchinner@xxxxxxxxxx>
> ---
> fs/xfs/xfs_buf.c | 91 +++++++++++++++++++++---------------------------
> 1 file changed, 39 insertions(+), 52 deletions(-)
>
> diff --git a/fs/xfs/xfs_buf.c b/fs/xfs/xfs_buf.c
> index 592800c8852f..a6cf607bbc4a 100644
> --- a/fs/xfs/xfs_buf.c
> +++ b/fs/xfs/xfs_buf.c
> @@ -276,8 +276,8 @@ _xfs_buf_alloc(
> * Allocate a page array capable of holding a specified number
> * of pages, and point the page buf at it.
> */
> -STATIC int
> -_xfs_buf_get_pages(
> +static int
> +xfs_buf_get_pages(
> struct xfs_buf *bp,
> int page_count)
> {
> @@ -292,8 +292,8 @@ _xfs_buf_get_pages(
> if (bp->b_pages == NULL)
> return -ENOMEM;
> }
> - memset(bp->b_pages, 0, sizeof(struct page *) * page_count);
> }
> + memset(bp->b_pages, 0, sizeof(struct page *) * bp->b_page_count);
Could this kmem_alloc be converted to kmem_zalloc?
And isn't the xfs_buf allocated with zalloc, which means we don't need
to zero b_page_array itself?
Confused about why this is needed.
> return 0;
> }
>
> @@ -356,10 +356,10 @@ xfs_buf_allocate_memory(
> uint flags)
> {
> size_t size;
> - size_t nbytes, offset;
> + size_t offset;
> gfp_t gfp_mask = xb_to_gfp(flags);
> - unsigned short page_count, i;
> xfs_off_t start, end;
> + long filled = 0;
> int error;
> xfs_km_flags_t kmflag_mask = 0;
>
> @@ -405,55 +405,44 @@ xfs_buf_allocate_memory(
> start = BBTOB(bp->b_maps[0].bm_bn) >> PAGE_SHIFT;
> end = (BBTOB(bp->b_maps[0].bm_bn + bp->b_length) + PAGE_SIZE - 1)
> >> PAGE_SHIFT;
> - page_count = end - start;
> - error = _xfs_buf_get_pages(bp, page_count);
> + error = xfs_buf_get_pages(bp, end - start);
> if (unlikely(error))
> return error;
>
> offset = bp->b_offset;
> bp->b_flags |= _XBF_PAGES;
>
> - for (i = 0; i < bp->b_page_count; i++) {
> - struct page *page;
> - uint retries = 0;
> -retry:
> - page = alloc_page(gfp_mask);
> - if (unlikely(page == NULL)) {
> - if (flags & XBF_READ_AHEAD) {
> - bp->b_page_count = i;
> - error = -ENOMEM;
> - goto out_free_pages;
> - }
> + /*
> + * Bulk filling of pages can take multiple calls. Not filling the entire
> + * array is not an allocation failure, so don't back off if we get at
> + * least one extra page.
> + */
> + for (;;) {
> + int last = filled;
Any reason why last is int but filled is long?
Oh, heh, nr_pages is int.
Nice how Dr. Demento came on as soon as I started reading
__alloc_pages_bulk.
>
> - /*
> - * This could deadlock.
> - *
> - * But until all the XFS lowlevel code is revamped to
> - * handle buffer allocation failures we can't do much.
> - */
> - if (!(++retries % 100))
> - xfs_err(NULL,
> - "%s(%u) possible memory allocation deadlock in %s (mode:0x%x)",
> - current->comm, current->pid,
> - __func__, gfp_mask);
> -
> - XFS_STATS_INC(bp->b_mount, xb_page_retries);
> - congestion_wait(BLK_RW_ASYNC, HZ/50);
> - goto retry;
> + filled = alloc_pages_bulk_array(gfp_mask, bp->b_page_count,
> + bp->b_pages);
> + if (filled == bp->b_page_count) {
> + XFS_STATS_INC(bp->b_mount, xb_page_found);
> + break;
> }
>
> - XFS_STATS_INC(bp->b_mount, xb_page_found);
> + if (filled != last)
> + continue;
>
> - nbytes = min_t(size_t, size, PAGE_SIZE - offset);
> - size -= nbytes;
> - bp->b_pages[i] = page;
> - offset = 0;
> + if (flags & XBF_READ_AHEAD) {
> + error = -ENOMEM;
> + goto out_free_pages;
> + }
> +
> + XFS_STATS_INC(bp->b_mount, xb_page_retries);
> + congestion_wait(BLK_RW_ASYNC, HZ/50);
Silly nit: spaces around HZ / 50.
Otherwise this mostly looks ok to me. The bulk allocation is a big
improvement.
--D
> }
> return 0;
>
> out_free_pages:
> - for (i = 0; i < bp->b_page_count; i++)
> - __free_page(bp->b_pages[i]);
> + while (--filled >= 0)
> + __free_page(bp->b_pages[filled]);
> bp->b_flags &= ~_XBF_PAGES;
> return error;
> }
> @@ -950,8 +939,8 @@ xfs_buf_get_uncached(
> int flags,
> struct xfs_buf **bpp)
> {
> - unsigned long page_count;
> - int error, i;
> + unsigned long filled;
> + int error;
> struct xfs_buf *bp;
> DEFINE_SINGLE_BUF_MAP(map, XFS_BUF_DADDR_NULL, numblks);
>
> @@ -962,17 +951,15 @@ xfs_buf_get_uncached(
> if (error)
> goto fail;
>
> - page_count = PAGE_ALIGN(numblks << BBSHIFT) >> PAGE_SHIFT;
> - error = _xfs_buf_get_pages(bp, page_count);
> + error = xfs_buf_get_pages(bp, PAGE_ALIGN(BBTOB(numblks)) >> PAGE_SHIFT);
> if (error)
> goto fail_free_buf;
>
> - for (i = 0; i < page_count; i++) {
> - bp->b_pages[i] = alloc_page(xb_to_gfp(flags));
> - if (!bp->b_pages[i]) {
> - error = -ENOMEM;
> - goto fail_free_mem;
> - }
> + filled = alloc_pages_bulk_array(xb_to_gfp(flags), bp->b_page_count,
> + bp->b_pages);
> + if (filled != bp->b_page_count) {
> + error = -ENOMEM;
> + goto fail_free_mem;
> }
> bp->b_flags |= _XBF_PAGES;
>
> @@ -988,8 +975,8 @@ xfs_buf_get_uncached(
> return 0;
>
> fail_free_mem:
> - while (--i >= 0)
> - __free_page(bp->b_pages[i]);
> + while (--filled >= 0)
> + __free_page(bp->b_pages[filled]);
> _xfs_buf_free_pages(bp);
> fail_free_buf:
> xfs_buf_free_maps(bp);
> --
> 2.31.1
>
