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xfs: Fix overallocation in xfs_buf_allocate_memory()

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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>
This commit is contained in:
Jan Kara 2012-06-06 00:32:26 +02:00 committed by Ben Myers
parent 079da28c64
commit bcf62ab64d
1 changed files with 2 additions and 14 deletions
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16
fs/xfs/xfs_buf.c
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@ -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;