xfs: get rid of unnecessary xfs_perag_{get,put} pairs

In the course of some operations, we look up the perag from
the mount multiple times to get or change perag information.
These are often very short pieces of code, so while the
lookup cost is generally low, the cost of the lookup is far
higher than the cost of the operation we are doing on the
perag.

Since we changed buffers to hold references to the perag
they are cached in, many modification contexts already hold
active references to the perag that are held across these
operations. This is especially true for any operation that
is serialised by an allocation group header buffer.

In these cases, we can just use the buffer's reference to
the perag to avoid needing to do lookups to access the
perag. This means that many operations don't need to do
perag lookups at all to access the perag because they've
already looked up objects that own persistent references
and hence can use that reference instead.

Cc: Dave Chinner <dchinner@redhat.com>
Cc: "Darrick J. Wong" <darrick.wong@oracle.com>
Signed-off-by: Gao Xiang <hsiangkao@redhat.com>
Reviewed-by: Darrick J. Wong <darrick.wong@oracle.com>
Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>

1 files changed, 7 insertions, 15 deletions

diff --git a/fs/xfs/libxfs/xfs_alloc.c b/fs/xfs/libxfs/xfs_alloc.c
index 203e74fa64aa..bf4d07e5c73f 100644
--- a/fs/xfs/libxfs/xfs_alloc.c
+++ b/fs/xfs/libxfs/xfs_alloc.c
@@ -710,13 +710,12 @@ xfs_alloc_read_agfl(
 STATIC int
 xfs_alloc_update_counters(
 	struct xfs_trans	*tp,
-	struct xfs_perag	*pag,
 	struct xfs_buf		*agbp,
 	long			len)
 {
 	struct xfs_agf		*agf = agbp->b_addr;
 
-	pag->pagf_freeblks += len;
+	agbp->b_pag->pagf_freeblks += len;
 	be32_add_cpu(&agf->agf_freeblks, len);
 
 	xfs_trans_agblocks_delta(tp, len);
@@ -1175,8 +1174,7 @@ xfs_alloc_ag_vextent(
 	}
 
 	if (!args->wasfromfl) {
-		error = xfs_alloc_update_counters(args->tp, args->pag,
-						  args->agbp,
+		error = xfs_alloc_update_counters(args->tp, args->agbp,
 						  -((long)(args->len)));
 		if (error)
 			return error;
@@ -1887,7 +1885,6 @@ xfs_free_ag_extent(
 	enum xfs_ag_resv_type		type)
 {
 	struct xfs_mount		*mp;
-	struct xfs_perag		*pag;
 	struct xfs_btree_cur		*bno_cur;
 	struct xfs_btree_cur		*cnt_cur;
 	xfs_agblock_t			gtbno; /* start of right neighbor */
@@ -2167,10 +2164,8 @@ xfs_free_ag_extent(
 	/*
 	 * Update the freespace totals in the ag and superblock.
 	 */
-	pag = xfs_perag_get(mp, agno);
-	error = xfs_alloc_update_counters(tp, pag, agbp, len);
-	xfs_ag_resv_free_extent(pag, type, tp, len);
-	xfs_perag_put(pag);
+	error = xfs_alloc_update_counters(tp, agbp, len);
+	xfs_ag_resv_free_extent(agbp->b_pag, type, tp, len);
 	if (error)
 		goto error0;
 
@@ -2689,7 +2684,7 @@ xfs_alloc_get_freelist(
 	if (be32_to_cpu(agf->agf_flfirst) == xfs_agfl_size(mp))
 		agf->agf_flfirst = 0;
 
-	pag = xfs_perag_get(mp, be32_to_cpu(agf->agf_seqno));
+	pag = agbp->b_pag;
 	ASSERT(!pag->pagf_agflreset);
 	be32_add_cpu(&agf->agf_flcount, -1);
 	xfs_trans_agflist_delta(tp, -1);
@@ -2701,7 +2696,6 @@ xfs_alloc_get_freelist(
 		pag->pagf_btreeblks++;
 		logflags |= XFS_AGF_BTREEBLKS;
 	}
-	xfs_perag_put(pag);
 
 	xfs_alloc_log_agf(tp, agbp, logflags);
 	*bnop = bno;
@@ -2797,7 +2791,7 @@ xfs_alloc_put_freelist(
 	if (be32_to_cpu(agf->agf_fllast) == xfs_agfl_size(mp))
 		agf->agf_fllast = 0;
 
-	pag = xfs_perag_get(mp, be32_to_cpu(agf->agf_seqno));
+	pag = agbp->b_pag;
 	ASSERT(!pag->pagf_agflreset);
 	be32_add_cpu(&agf->agf_flcount, 1);
 	xfs_trans_agflist_delta(tp, 1);
@@ -2809,7 +2803,6 @@ xfs_alloc_put_freelist(
 		pag->pagf_btreeblks--;
 		logflags |= XFS_AGF_BTREEBLKS;
 	}
-	xfs_perag_put(pag);
 
 	xfs_alloc_log_agf(tp, agbp, logflags);
 
@@ -3006,7 +2999,7 @@ xfs_alloc_read_agf(
 	ASSERT(!(*bpp)->b_error);
 
 	agf = (*bpp)->b_addr;
-	pag = xfs_perag_get(mp, agno);
+	pag = (*bpp)->b_pag;
 	if (!pag->pagf_init) {
 		pag->pagf_freeblks = be32_to_cpu(agf->agf_freeblks);
 		pag->pagf_btreeblks = be32_to_cpu(agf->agf_btreeblks);
@@ -3034,7 +3027,6 @@ xfs_alloc_read_agf(
 		       be32_to_cpu(agf->agf_levels[XFS_BTNUM_CNTi]));
 	}
 #endif
-	xfs_perag_put(pag);
 	return 0;
 }