On Thu, May 27, 2021 at 03:59:51PM -0700, Darrick J. Wong wrote:
> 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:
Never mind, you fixed all this in the next patch, which my grep didn't
find. Question withdrawn.
--D
>
> 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
> >
