xfs: Fix overallocation in xfs_buf_allocate_memory() (59c84ed0) · Commits · 戴 / test

Commit 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>

fs/xfs/xfs_buf.c

+2 −14

Original line number	Diff line number	Diff line
		@@ -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;

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