[PATCH 07/11] xfs: simplify the b_page_count calculation

[Christoph Hellwig <hch@xxxxxx>]

Ever since we stopped using the Linux page cache to back XFS buffes
there is no need to take the start sector into account for calculating
the number of pages in a buffer, as the data always start from the
beginning of the buffer.

Signed-off-by: Christoph Hellwig <hch@xxxxxx>
---
 fs/xfs/xfs_buf.c | 26 +++++++++-----------------
 1 file changed, 9 insertions(+), 17 deletions(-)

diff --git a/fs/xfs/xfs_buf.c b/fs/xfs/xfs_buf.c
index 08c8667e6027fc..76a107e3cb2a22 100644
--- a/fs/xfs/xfs_buf.c
+++ b/fs/xfs/xfs_buf.c
@@ -278,15 +278,14 @@ _xfs_buf_alloc(
  */
 STATIC int
 _xfs_buf_get_pages(
-	struct xfs_buf		*bp,
-	int			page_count)
+	struct xfs_buf		*bp)
 {
 	ASSERT(bp->b_pages == NULL);
 
-	bp->b_page_count = page_count;
-	if (page_count > XB_PAGES) {
-		bp->b_pages = kmem_zalloc(sizeof(struct page *) * page_count,
-					  KM_NOFS);
+	bp->b_page_count = DIV_ROUND_UP(BBTOB(bp->b_length), PAGE_SIZE);
+	if (bp->b_page_count > XB_PAGES) {
+		bp->b_pages = kmem_zalloc(sizeof(struct page *) *
+						bp->b_page_count, KM_NOFS);
 		if (!bp->b_pages)
 			return -ENOMEM;
 	} else {
@@ -384,8 +383,7 @@ xfs_buf_alloc_pages(
 	uint			flags)
 {
 	gfp_t			gfp_mask = xb_to_gfp(flags);
-	unsigned short		page_count, i;
-	xfs_off_t		start, end;
+	unsigned short		i;
 	int			error;
 
 	/*
@@ -394,11 +392,7 @@ xfs_buf_alloc_pages(
 	if (!(flags & XBF_READ))
 		gfp_mask |= __GFP_ZERO;
 
-	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);
 	if (unlikely(error))
 		return error;
 
@@ -942,7 +936,6 @@ xfs_buf_get_uncached(
 	int			flags,
 	struct xfs_buf		**bpp)
 {
-	unsigned long		page_count;
 	int			error, i;
 	struct xfs_buf		*bp;
 	DEFINE_SINGLE_BUF_MAP(map, XFS_BUF_DADDR_NULL, numblks);
@@ -954,12 +947,11 @@ 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);
 	if (error)
 		goto fail_free_buf;
 
-	for (i = 0; i < page_count; i++) {
+	for (i = 0; i < bp->b_page_count; i++) {
 		bp->b_pages[i] = alloc_page(xb_to_gfp(flags));
 		if (!bp->b_pages[i]) {
 			error = -ENOMEM;
-- 
2.30.2