On Thu, May 27, 2021 at 03:48:58PM -0700, Darrick J. Wong wrote:
> On Thu, May 27, 2021 at 08:47:13AM +1000, Dave Chinner wrote:
> > From: Dave Chinner <dchinner@xxxxxxxxxx>
> >
> > Based on a patch from Christoph Hellwig.
> >
> > This splits out the heap allocation and page allocation portions of
> > the buffer memory allocation into two separate helper functions.
> >
> > Signed-off-by: Dave Chinner <dchinner@xxxxxxxxxx>
> > ---
> > fs/xfs/xfs_buf.c | 126 ++++++++++++++++++++++++++++-------------------
> > 1 file changed, 74 insertions(+), 52 deletions(-)
> >
> > diff --git a/fs/xfs/xfs_buf.c b/fs/xfs/xfs_buf.c
> > index 592800c8852f..2e35d344a69b 100644
> > --- a/fs/xfs/xfs_buf.c
> > +++ b/fs/xfs/xfs_buf.c
> > @@ -347,65 +347,55 @@ xfs_buf_free(
> > kmem_cache_free(xfs_buf_zone, bp);
> > }
> >
> > -/*
> > - * Allocates all the pages for buffer in question and builds it's page list.
> > - */
> > -STATIC int
> > -xfs_buf_allocate_memory(
> > - struct xfs_buf *bp,
> > - uint flags)
> > +static int
> > +xfs_buf_alloc_kmem(
> > + struct xfs_buf *bp,
> > + size_t size,
> > + xfs_buf_flags_t flags)
> > {
> > - size_t size;
> > - size_t nbytes, offset;
> > - gfp_t gfp_mask = xb_to_gfp(flags);
> > - unsigned short page_count, i;
> > - xfs_off_t start, end;
> > - int error;
> > - xfs_km_flags_t kmflag_mask = 0;
> > + int align_mask = xfs_buftarg_dma_alignment(bp->b_target);
> > + xfs_km_flags_t kmflag_mask = KM_NOFS;
> >
> > - /*
> > - * assure zeroed buffer for non-read cases.
> > - */
> > - if (!(flags & XBF_READ)) {
> > + /* Assure zeroed buffer for non-read cases. */
> > + if (!(flags & XBF_READ))
> > kmflag_mask |= KM_ZERO;
> > - gfp_mask |= __GFP_ZERO;
> > - }
> >
> > - /*
> > - * for buffers that are contained within a single page, just allocate
> > - * the memory from the heap - there's no need for the complexity of
> > - * page arrays to keep allocation down to order 0.
> > - */
> > - size = BBTOB(bp->b_length);
> > - if (size < PAGE_SIZE) {
> > - int align_mask = xfs_buftarg_dma_alignment(bp->b_target);
> > - bp->b_addr = kmem_alloc_io(size, align_mask,
> > - KM_NOFS | kmflag_mask);
> > - if (!bp->b_addr) {
> > - /* low memory - use alloc_page loop instead */
> > - goto use_alloc_page;
> > - }
> > + bp->b_addr = kmem_alloc_io(size, align_mask, kmflag_mask);
> > + if (!bp->b_addr)
> > + return -ENOMEM;
> >
> > - if (((unsigned long)(bp->b_addr + size - 1) & PAGE_MASK) !=
> > - ((unsigned long)bp->b_addr & PAGE_MASK)) {
> > - /* b_addr spans two pages - use alloc_page instead */
> > - kmem_free(bp->b_addr);
> > - bp->b_addr = NULL;
> > - goto use_alloc_page;
> > - }
> > - bp->b_offset = offset_in_page(bp->b_addr);
> > - bp->b_pages = bp->b_page_array;
> > - bp->b_pages[0] = kmem_to_page(bp->b_addr);
> > - bp->b_page_count = 1;
> > - bp->b_flags |= _XBF_KMEM;
> > - return 0;
> > + if (((unsigned long)(bp->b_addr + size - 1) & PAGE_MASK) !=
> > + ((unsigned long)bp->b_addr & PAGE_MASK)) {
> > + /* b_addr spans two pages - use alloc_page instead */
> > + kmem_free(bp->b_addr);
> > + bp->b_addr = NULL;
> > + return -ENOMEM;
> > }
> > + bp->b_offset = offset_in_page(bp->b_addr);
> > + bp->b_pages = bp->b_page_array;
> > + bp->b_pages[0] = kmem_to_page(bp->b_addr);
> > + bp->b_page_count = 1;
> > + bp->b_flags |= _XBF_KMEM;
> > + return 0;
> > +}
> > +
> > +static int
> > +xfs_buf_alloc_pages(
> > + struct xfs_buf *bp,
> > + uint page_count,
> > + xfs_buf_flags_t flags)
> > +{
> > + gfp_t gfp_mask = xb_to_gfp(flags);
> > + size_t size;
> > + size_t offset;
> > + size_t nbytes;
> > + int i;
> > + int error;
> > +
> > + /* Assure zeroed buffer for non-read cases. */
> > + if (!(flags & XBF_READ))
> > + gfp_mask |= __GFP_ZERO;
> >
> > -use_alloc_page:
> > - 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);
> > if (unlikely(error))
> > return error;
> > @@ -458,6 +448,38 @@ xfs_buf_allocate_memory(
> > return error;
> > }
> >
> > +
> > +/*
> > + * Allocates all the pages for buffer in question and builds it's page list.
> > + */
> > +static int
> > +xfs_buf_allocate_memory(
> > + struct xfs_buf *bp,
> > + uint flags)
> > +{
> > + size_t size;
> > + xfs_off_t start, end;
> > + int error;
> > +
> > + /*
> > + * For buffers that fit entirely within a single page, first attempt to
> > + * allocate the memory from the heap to minimise memory usage. If we
> > + * can't get heap memory for these small buffers, we fall back to using
> > + * the page allocator.
> > + */
> > + size = BBTOB(bp->b_length);
> > + if (size < PAGE_SIZE) {
> > + error = xfs_buf_alloc_kmem(bp, size, flags);
> > + if (!error)
> > + return 0;
> > + }
> > +
> > + 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;
>
> round_down and round_up?
>
> As a straight translation this seems fine, but you might as well take
> the opportunity to declutter some of this. :)
...which you & hch did in patch 7. Ok.
> Reviewed-by: Darrick J. Wong <djwong@xxxxxxxxxx>
>
> --D
>
> > + return xfs_buf_alloc_pages(bp, end - start, flags);
> > +}
> > +
> > /*
> > * Map buffer into kernel address-space if necessary.
> > */
> > --
> > 2.31.1
> >
