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[PATCH] xfs: Fix overallocation in xfs_buf_allocate_memory()

To: xfs@xxxxxxxxxxx
Subject: [PATCH] xfs: Fix overallocation in xfs_buf_allocate_memory()
From: Jan Kara <jack@xxxxxxx>
Date: Tue, 5 Jun 2012 13:08:10 +0200
Cc: Ben Myers <bpm@xxxxxxx>, Alex Elder <elder@xxxxxxxxxx>, Jan Kara <jack@xxxxxxx>
Commit 0e6e847f which introduced xfs_buf_allocate_memory() function has a bug
causing the function to overestimate the number of necessary pages. The problem
is that xfs_buf_alloc() sets b_bn to -1 and thus effectively every buffer is
straddling a page boundary which causes xfs_buf_allocate_memory() to allocate
two pages and use vmalloc() for access which slows things down.

Fix the code to use correct block number.

Signed-off-by: Jan Kara <jack@xxxxxxx>
---
 fs/xfs/xfs_buf.c |    7 ++++---
 1 files changed, 4 insertions(+), 3 deletions(-)

diff --git a/fs/xfs/xfs_buf.c b/fs/xfs/xfs_buf.c
index 172d3cc..b67cc83 100644
--- a/fs/xfs/xfs_buf.c
+++ b/fs/xfs/xfs_buf.c
@@ -296,6 +296,7 @@ xfs_buf_free(
 STATIC int
 xfs_buf_allocate_memory(
        xfs_buf_t               *bp,
+       xfs_daddr_t             blkno,
        uint                    flags)
 {
        size_t                  size;
@@ -334,8 +335,8 @@ xfs_buf_allocate_memory(
        }
 
 use_alloc_page:
-       start = BBTOB(bp->b_bn) >> PAGE_SHIFT;
-       end = (BBTOB(bp->b_bn + bp->b_length) + PAGE_SIZE - 1) >> PAGE_SHIFT;
+       start = BBTOB(blkno) >> PAGE_SHIFT;
+       end = (BBTOB(blkno + bp->b_length) + PAGE_SIZE - 1) >> PAGE_SHIFT;
        page_count = end - start;
        error = _xfs_buf_get_pages(bp, page_count, flags);
        if (unlikely(error))
@@ -552,7 +553,7 @@ xfs_buf_get(
        if (unlikely(!new_bp))
                return NULL;
 
-       error = xfs_buf_allocate_memory(new_bp, flags);
+       error = xfs_buf_allocate_memory(new_bp, blkno, flags);
        if (error) {
                kmem_zone_free(xfs_buf_zone, new_bp);
                return NULL;
-- 
1.7.1

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