GFS2: Set of distributed preferences for rgrps

This patch tries to use the journal numbers to evenly distribute
which node prefers which resource group for block allocations. This
is to help performance.

Signed-off-by: Bob Peterson <rpeterso@redhat.com>
Signed-off-by: Steven Whitehouse <swhiteho@redhat.com>

fs/gfs2/incore.h

@@ -97,6 +97,7 @@ struct gfs2_rgrpd {
 #define GFS2_RDF_CHECK		0x10000000 /* check for unlinked inodes */
 #define GFS2_RDF_UPTODATE	0x20000000 /* rg is up to date */
 #define GFS2_RDF_ERROR		0x40000000 /* error in rg */
+#define GFS2_RDF_PREFERRED	0x80000000 /* This rgrp is preferred */
 #define GFS2_RDF_MASK		0xf0000000 /* mask for internal flags */
 	spinlock_t rd_rsspin;           /* protects reservation related vars */
 	struct rb_root rd_rstree;       /* multi-block reservation tree */

fs/gfs2/rgrp.c

@@ -936,7 +936,7 @@ static int read_rindex_entry(struct gfs2_inode *ip)
 	rgd->rd_gl->gl_vm.start = rgd->rd_addr * bsize;
 	rgd->rd_gl->gl_vm.end = rgd->rd_gl->gl_vm.start + (rgd->rd_length * bsize) - 1;
 	rgd->rd_rgl = (struct gfs2_rgrp_lvb *)rgd->rd_gl->gl_lksb.sb_lvbptr;
-	rgd->rd_flags &= ~GFS2_RDF_UPTODATE;
+	rgd->rd_flags &= ~(GFS2_RDF_UPTODATE | GFS2_RDF_PREFERRED);
 	if (rgd->rd_data > sdp->sd_max_rg_data)
 		sdp->sd_max_rg_data = rgd->rd_data;
 	spin_lock(&sdp->sd_rindex_spin);
@@ -954,6 +954,36 @@ fail:
 	return error;
 }
 
+/**
+ * set_rgrp_preferences - Run all the rgrps, selecting some we prefer to use
+ * @sdp: the GFS2 superblock
+ *
+ * The purpose of this function is to select a subset of the resource groups
+ * and mark them as PREFERRED. We do it in such a way that each node prefers
+ * to use a unique set of rgrps to minimize glock contention.
+ */
+static void set_rgrp_preferences(struct gfs2_sbd *sdp)
+{
+	struct gfs2_rgrpd *rgd, *first;
+	int i;
+
+	/* Skip an initial number of rgrps, based on this node's journal ID.
+	   That should start each node out on its own set. */
+	rgd = gfs2_rgrpd_get_first(sdp);
+	for (i = 0; i < sdp->sd_lockstruct.ls_jid; i++)
+		rgd = gfs2_rgrpd_get_next(rgd);
+	first = rgd;
+
+	do {
+		rgd->rd_flags |= GFS2_RDF_PREFERRED;
+		for (i = 0; i < sdp->sd_journals; i++) {
+			rgd = gfs2_rgrpd_get_next(rgd);
+			if (rgd == first)
+				break;
+		}
+	} while (rgd != first);
+}
+
 /**
  * gfs2_ri_update - Pull in a new resource index from the disk
  * @ip: pointer to the rindex inode
@@ -973,6 +1003,8 @@ static int gfs2_ri_update(struct gfs2_inode *ip)
 	if (error < 0)
 		return error;
 
+	set_rgrp_preferences(sdp);
+
 	sdp->sd_rindex_uptodate = 1;
 	return 0;
 }
@@ -1890,6 +1922,25 @@ static bool gfs2_select_rgrp(struct gfs2_rgrpd **pos, const struct gfs2_rgrpd *b
 	return false;
 }
 
+/**
+ * fast_to_acquire - determine if a resource group will be fast to acquire
+ *
+ * If this is one of our preferred rgrps, it should be quicker to acquire,
+ * because we tried to set ourselves up as dlm lock master.
+ */
+static inline int fast_to_acquire(struct gfs2_rgrpd *rgd)
+{
+	struct gfs2_glock *gl = rgd->rd_gl;
+
+	if (gl->gl_state != LM_ST_UNLOCKED && list_empty(&gl->gl_holders) &&
+	    !test_bit(GLF_DEMOTE_IN_PROGRESS, &gl->gl_flags) &&
+	    !test_bit(GLF_DEMOTE, &gl->gl_flags))
+		return 1;
+	if (rgd->rd_flags & GFS2_RDF_PREFERRED)
+		return 1;
+	return 0;
+}
+
 /**
  * gfs2_inplace_reserve - Reserve space in the filesystem
  * @ip: the inode to reserve space for
@@ -1932,10 +1983,15 @@ int gfs2_inplace_reserve(struct gfs2_inode *ip, const struct gfs2_alloc_parms *a
 			rg_locked = 0;
 			if (skip && skip--)
 				goto next_rgrp;
-			if (!gfs2_rs_active(rs) && (loops < 2) &&
-			     gfs2_rgrp_used_recently(rs, 1000) &&
-			     gfs2_rgrp_congested(rs->rs_rbm.rgd, loops))
-				goto next_rgrp;
+			if (!gfs2_rs_active(rs)) {
+				if (loops == 0 &&
+				    !fast_to_acquire(rs->rs_rbm.rgd))
+					goto next_rgrp;
+				if ((loops < 2) &&
+				    gfs2_rgrp_used_recently(rs, 1000) &&
+				    gfs2_rgrp_congested(rs->rs_rbm.rgd, loops))
+					goto next_rgrp;
+			}
 			error = gfs2_glock_nq_init(rs->rs_rbm.rgd->rd_gl,
 						   LM_ST_EXCLUSIVE, flags,
 						   &rs->rs_rgd_gh);