On Thu, May 27, 2021 at 08:47:15AM +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 | 62 +++++++++++++++++++-----------------------------
> 1 file changed, 24 insertions(+), 38 deletions(-)
>
> diff --git a/fs/xfs/xfs_buf.c b/fs/xfs/xfs_buf.c
> index b1610115d401..8ca4add138c5 100644
> --- a/fs/xfs/xfs_buf.c
> +++ b/fs/xfs/xfs_buf.c
> @@ -386,10 +386,7 @@ xfs_buf_alloc_pages(
> xfs_buf_flags_t flags)
> {
> gfp_t gfp_mask = xb_to_gfp(flags);
> - size_t size;
> - size_t offset;
> - size_t nbytes;
> - int i;
> + long filled = 0;
> int error;
>
> /* Assure zeroed buffer for non-read cases. */
> @@ -400,50 +397,39 @@ xfs_buf_alloc_pages(
> 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 (;;) {
> + long last = filled;
>
> - /*
> - * 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);
Nit: spaces around operators ("HZ / 50").
With that fixed,
Reviewed-by: Darrick J. Wong <djwong@xxxxxxxxxx>
I have a question about _xfs_buf_get_pages:
STATIC int
_xfs_buf_get_pages(
struct xfs_buf *bp,
int page_count)
{
/* Make sure that we have a page list */
if (bp->b_pages == NULL) {
bp->b_page_count = page_count;
if (page_count <= XB_PAGES) {
bp->b_pages = bp->b_page_array;
} else {
bp->b_pages = kmem_alloc(sizeof(struct page *) *
page_count, KM_NOFS);
if (bp->b_pages == NULL)
return -ENOMEM;
}
memset(bp->b_pages, 0, sizeof(struct page *) * page_count);
}
return 0;
}
xfs_bufs are kmem_cache_zalloc'd, which means that b_page_array should
be zeroed, right?
And we could use kmem_zalloc for the pagecount > XB_PAGES case, which
would make the memset necessary, wouldn't it?
OFC that only holds if a buffer that fails the memory allocation is
immediately fed to _xfs_buf_free_pages to null out b_pages, which I
think is true...?
--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;
> }
> --
> 2.31.1
>
