[Cluster-devel] [GFS2 PATCH] GFS2: Speed up gfs2_rbm_from_block

[Bob Peterson <rpeterso@redhat.com>]

Hi,

This patch is a rewrite of function gfs2_rbm_from_block. Rather than
looping to find the right bitmap, the code now does a few simple
math calculations. This speeds up the function significantly.

Regards,

Bob Peterson
Red Hat File Systems

Signed-off-by: Bob Peterson <rpeterso@redhat.com> 
---
diff --git a/fs/gfs2/incore.h b/fs/gfs2/incore.h
index 3d469d3..24bb0b8 100644
--- a/fs/gfs2/incore.h
+++ b/fs/gfs2/incore.h
@@ -621,6 +621,7 @@ struct gfs2_sbd {
 	u32 sd_hash_bsize_shift;
 	u32 sd_hash_ptrs;	/* Number of pointers in a hash block */
 	u32 sd_qc_per_block;
+	u32 sd_blocks_per_bitmap;
 	u32 sd_max_dirres;	/* Max blocks needed to add a directory entry */
 	u32 sd_max_height;	/* Max height of a file's metadata tree */
 	u64 sd_heightsize[GFS2_MAX_META_HEIGHT + 1];
diff --git a/fs/gfs2/ops_fstype.c b/fs/gfs2/ops_fstype.c
index e443966..0e3554e 100644
--- a/fs/gfs2/ops_fstype.c
+++ b/fs/gfs2/ops_fstype.c
@@ -278,6 +278,9 @@ static int gfs2_read_sb(struct gfs2_sbd *sdp, int silent)
 	sdp->sd_qc_per_block = (sdp->sd_sb.sb_bsize -
 				sizeof(struct gfs2_meta_header)) /
 			        sizeof(struct gfs2_quota_change);
+	sdp->sd_blocks_per_bitmap = (sdp->sd_sb.sb_bsize -
+				     sizeof(struct gfs2_meta_header))
+		* GFS2_NBBY; /* not the rgrp bitmap, subsequent bitmaps only */
 
 	/* Compute maximum reservation required to add a entry to a directory */
 
diff --git a/fs/gfs2/rgrp.c b/fs/gfs2/rgrp.c
index 43d1a20..7635500 100644
--- a/fs/gfs2/rgrp.c
+++ b/fs/gfs2/rgrp.c
@@ -250,23 +250,23 @@ static u32 gfs2_bitfit(const u8 *buf, const unsigned int len,
 
 static int gfs2_rbm_from_block(struct gfs2_rbm *rbm, u64 block)
 {
-	u64 rblock = block - rbm->rgd->rd_data0;
-	u32 goal = (u32)rblock;
-	int x;
+	u32 x;
 
-	if (WARN_ON_ONCE(rblock > UINT_MAX))
-		return -EINVAL;
 	if (block >= rbm->rgd->rd_data0 + rbm->rgd->rd_data)
 		return -E2BIG;
 
-	for (x = 0; x < rbm->rgd->rd_length; x++) {
-		rbm->bi = rbm->rgd->rd_bits + x;
-		if (goal < (rbm->bi->bi_start + rbm->bi->bi_len) * GFS2_NBBY) {
-			rbm->offset = goal - (rbm->bi->bi_start * GFS2_NBBY);
-			break;
-		}
-	}
+	rbm->bi = rbm->rgd->rd_bits;
+	rbm->offset = (u32)(block - rbm->rgd->rd_data0);
+	/* Check if the block is within the first block */
+	if (rbm->offset < (rbm->bi->bi_start + rbm->bi->bi_len) * GFS2_NBBY)
+		return 0;
 
+	/* Adjust for the size diff between gfs2_meta_header and gfs2_rgrp */
+	rbm->offset += (sizeof(struct gfs2_rgrp) -
+			sizeof(struct gfs2_meta_header)) * GFS2_NBBY;
+	x = rbm->offset / rbm->rgd->rd_sbd->sd_blocks_per_bitmap;
+	rbm->offset -= x * rbm->rgd->rd_sbd->sd_blocks_per_bitmap;
+	rbm->bi += x;
 	return 0;
 }