GFS2: Metadata address space clean up

Since the start of GFS2, an "extra" inode has been used to store
the metadata belonging to each inode. The only reason for using
this inode was to have an extra address space, the other fields
were unused. This means that the memory usage was rather inefficient.

The reason for keeping each inode's metadata in a separate address
space is that when glocks are requested on remote nodes, we need to
be able to efficiently locate the data and metadata which relating
to that glock (inode) in order to sync or sync and invalidate it
(depending on the remotely requested lock mode).

This patch adds a new type of glock, which has in addition to
its normal fields, has an address space. This applies to all
inode and rgrp glocks (but to no other glock types which remain
as before). As a result, we no longer need to have the second
inode.

This results in three major improvements:
 1. A saving of approx 25% of memory used in caching inodes
 2. A removal of the circular dependency between inodes and glocks
 3. No confusion between "normal" and "metadata" inodes in super.c

Although the first of these is the more immediately apparent, the
second is just as important as it now enables a number of clean
ups at umount time. Those will be the subject of future patches.

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

1 files changed, 21 insertions, 19 deletions

diff --git a/fs/gfs2/glock.c b/fs/gfs2/glock.c
index f4266332593..dfb10a4d467 100644
--- a/fs/gfs2/glock.c
+++ b/fs/gfs2/glock.c
@@ -154,12 +154,14 @@ static unsigned int gl_hash(const struct gfs2_sbd *sdp,
 static void glock_free(struct gfs2_glock *gl)
 {
 	struct gfs2_sbd *sdp = gl->gl_sbd;
-	struct inode *aspace = gl->gl_aspace;
+	struct address_space *mapping = gfs2_glock2aspace(gl);
+	struct kmem_cache *cachep = gfs2_glock_cachep;
 
-	if (aspace)
-		gfs2_aspace_put(aspace);
+	GLOCK_BUG_ON(gl, mapping && mapping->nrpages);
 	trace_gfs2_glock_put(gl);
-	sdp->sd_lockstruct.ls_ops->lm_put_lock(gfs2_glock_cachep, gl);
+	if (mapping)
+		cachep = gfs2_glock_aspace_cachep;
+	sdp->sd_lockstruct.ls_ops->lm_put_lock(cachep, gl);
 }
 
 /**
@@ -750,10 +752,11 @@ int gfs2_glock_get(struct gfs2_sbd *sdp, u64 number,
 		   const struct gfs2_glock_operations *glops, int create,
 		   struct gfs2_glock **glp)
 {
+	struct super_block *s = sdp->sd_vfs;
 	struct lm_lockname name = { .ln_number = number, .ln_type = glops->go_type };
 	struct gfs2_glock *gl, *tmp;
 	unsigned int hash = gl_hash(sdp, &name);
-	int error;
+	struct address_space *mapping;
 
 	read_lock(gl_lock_addr(hash));
 	gl = search_bucket(hash, sdp, &name);
@@ -765,7 +768,10 @@ int gfs2_glock_get(struct gfs2_sbd *sdp, u64 number,
 	if (!create)
 		return -ENOENT;
 
-	gl = kmem_cache_alloc(gfs2_glock_cachep, GFP_KERNEL);
+	if (glops->go_flags & GLOF_ASPACE)
+		gl = kmem_cache_alloc(gfs2_glock_aspace_cachep, GFP_KERNEL);
+	else
+		gl = kmem_cache_alloc(gfs2_glock_cachep, GFP_KERNEL);
 	if (!gl)
 		return -ENOMEM;
 
@@ -784,18 +790,18 @@ int gfs2_glock_get(struct gfs2_sbd *sdp, u64 number,
 	gl->gl_tchange = jiffies;
 	gl->gl_object = NULL;
 	gl->gl_sbd = sdp;
-	gl->gl_aspace = NULL;
 	INIT_DELAYED_WORK(&gl->gl_work, glock_work_func);
 	INIT_WORK(&gl->gl_delete, delete_work_func);
 
-	/* If this glock protects actual on-disk data or metadata blocks,
-	   create a VFS inode to manage the pages/buffers holding them. */
-	if (glops == &gfs2_inode_glops || glops == &gfs2_rgrp_glops) {
-		gl->gl_aspace = gfs2_aspace_get(sdp);
-		if (!gl->gl_aspace) {
-			error = -ENOMEM;
-			goto fail;
-		}
+	mapping = gfs2_glock2aspace(gl);
+	if (mapping) {
+                mapping->a_ops = &gfs2_meta_aops;
+		mapping->host = s->s_bdev->bd_inode;
+		mapping->flags = 0;
+		mapping_set_gfp_mask(mapping, GFP_NOFS);
+		mapping->assoc_mapping = NULL;
+		mapping->backing_dev_info = s->s_bdi;
+		mapping->writeback_index = 0;
 	}
 
 	write_lock(gl_lock_addr(hash));
@@ -812,10 +818,6 @@ int gfs2_glock_get(struct gfs2_sbd *sdp, u64 number,
 	*glp = gl;
 
 	return 0;
-
-fail:
-	kmem_cache_free(gfs2_glock_cachep, gl);
-	return error;
 }
 
 /**