xfs: Fix overallocation in xfs_buf_allocate_memory()

Commit de1cbee which removed b_file_offset in favor of b_bn introduced a bug
causing xfs_buf_allocate_memory() 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 is unnecessary.

Dave says xfs_buf_alloc() doesn't need to set b_bn to -1 anymore since the
buffer is inserted into the cache only after being fully initialized now.
So just make xfs_buf_alloc() fill in proper block number from the beginning.

CC: David Chinner <dchinner@redhat.com>
Signed-off-by: Jan Kara <jack@suse.cz>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Dave Chinner <dchinner@redhat.com>
Signed-off-by: Ben Myers <bpm@sgi.com>

1 files changed, 2 insertions, 14 deletions

diff --git a/fs/xfs/xfs_buf.c b/fs/xfs/xfs_buf.c
index 172d3cc8f8cb..a4beb421018a 100644
--- a/fs/xfs/xfs_buf.c
+++ b/fs/xfs/xfs_buf.c
@@ -201,14 +201,7 @@ xfs_buf_alloc(
         bp->b_length = numblks;
         bp->b_io_length = numblks;
         bp->b_flags = flags;
-
-        /*
-         * We do not set the block number here in the buffer because we have not
-         * finished initialising the buffer. We insert the buffer into the cache
-         * in this state, so this ensures that we are unable to do IO on a
-         * buffer that hasn't been fully initialised.
-         */
-        bp->b_bn = XFS_BUF_DADDR_NULL;
+        bp->b_bn = blkno;
         atomic_set(&bp->b_pin_count, 0);
         init_waitqueue_head(&bp->b_waiters);
 
@@ -567,11 +560,6 @@ xfs_buf_get(
         if (bp != new_bp)
                 xfs_buf_free(new_bp);
 
-        /*
-         * Now we have a workable buffer, fill in the block number so
-         * that we can do IO on it.
-         */
-        bp->b_bn = blkno;
         bp->b_io_length = bp->b_length;
 
 found:
@@ -772,7 +760,7 @@ xfs_buf_get_uncached(
         int                     error, i;
         xfs_buf_t               *bp;
 
-        bp = xfs_buf_alloc(target, 0, numblks, 0);
+        bp = xfs_buf_alloc(target, XFS_BUF_DADDR_NULL, numblks, 0);
         if (unlikely(bp == NULL))
                 goto fail;