GFS2: Use only a single address space for rgrps

Prior to this patch, GFS2 had one address space for each rgrp,
stored in the glock. This patch changes them to use a single
address space in the super block. This therefore saves
(sizeof(struct address_space) * nr_of_rgrps) bytes of memory
and for large filesystems, that can be significant.

It would be nice to be able to do something similar and merge
the inode metadata address space into the same global
address space. However, that is rather more complicated as the
on-disk location doesn't have a 1:1 mapping with the inodes in
general. So while it could be done, it will be a more complicated
operation as it requires changing a lot more code paths.
Signed-off-by: Steven Whitehouse <swhiteho@redhat.com>

fs/gfs2/glops.c

@@ -133,7 +133,8 @@ void gfs2_ail_flush(struct gfs2_glock *gl, bool fsync)
 
 static void rgrp_go_sync(struct gfs2_glock *gl)
 {
-	struct address_space *metamapping = gfs2_glock2aspace(gl);
+	struct gfs2_sbd *sdp = gl->gl_sbd;
+	struct address_space *mapping = &sdp->sd_aspace;
 	struct gfs2_rgrpd *rgd;
 	int error;
 
@@ -141,10 +142,10 @@ static void rgrp_go_sync(struct gfs2_glock *gl)
 		return;
 	GLOCK_BUG_ON(gl, gl->gl_state != LM_ST_EXCLUSIVE);
 
-	gfs2_log_flush(gl->gl_sbd, gl);
-	filemap_fdatawrite_range(metamapping, gl->gl_vm.start, gl->gl_vm.end);
-	error = filemap_fdatawait_range(metamapping, gl->gl_vm.start, gl->gl_vm.end);
-        mapping_set_error(metamapping, error);
+	gfs2_log_flush(sdp, gl);
+	filemap_fdatawrite_range(mapping, gl->gl_vm.start, gl->gl_vm.end);
+	error = filemap_fdatawait_range(mapping, gl->gl_vm.start, gl->gl_vm.end);
+	mapping_set_error(mapping, error);
 	gfs2_ail_empty_gl(gl);
 
 	spin_lock(&gl->gl_spin);
@@ -166,10 +167,11 @@ static void rgrp_go_sync(struct gfs2_glock *gl)
 
 static void rgrp_go_inval(struct gfs2_glock *gl, int flags)
 {
-	struct address_space *mapping = gfs2_glock2aspace(gl);
+	struct gfs2_sbd *sdp = gl->gl_sbd;
+	struct address_space *mapping = &sdp->sd_aspace;
 
 	WARN_ON_ONCE(!(flags & DIO_METADATA));
-	gfs2_assert_withdraw(gl->gl_sbd, !atomic_read(&gl->gl_ail_count));
+	gfs2_assert_withdraw(sdp, !atomic_read(&gl->gl_ail_count));
 	truncate_inode_pages_range(mapping, gl->gl_vm.start, gl->gl_vm.end);
 
 	if (gl->gl_object) {
@@ -558,7 +560,7 @@ const struct gfs2_glock_operations gfs2_rgrp_glops = {
 	.go_unlock = gfs2_rgrp_go_unlock,
 	.go_dump = gfs2_rgrp_dump,
 	.go_type = LM_TYPE_RGRP,
-	.go_flags = GLOF_ASPACE | GLOF_LVB,
+	.go_flags = GLOF_LVB,
 };
 
 const struct gfs2_glock_operations gfs2_trans_glops = {

fs/gfs2/incore.h

@@ -736,6 +736,8 @@ struct gfs2_sbd {
 
 	/* Log stuff */
 
+	struct address_space sd_aspace;
+
 	spinlock_t sd_log_lock;
 
 	struct gfs2_trans *sd_log_tr;

fs/gfs2/lops.c

@@ -589,8 +589,12 @@ static int buf_lo_scan_elements(struct gfs2_jdesc *jd, unsigned int start,
 static void gfs2_meta_sync(struct gfs2_glock *gl)
 {
 	struct address_space *mapping = gfs2_glock2aspace(gl);
+	struct gfs2_sbd *sdp = gl->gl_sbd;
 	int error;
 
+	if (mapping == NULL)
+		mapping = &sdp->sd_aspace;
+
 	filemap_fdatawrite(mapping);
 	error = filemap_fdatawait(mapping);
 

fs/gfs2/meta_io.c

@@ -116,6 +116,9 @@ struct buffer_head *gfs2_getbuf(struct gfs2_glock *gl, u64 blkno, int create)
 	unsigned long index;
 	unsigned int bufnum;
 
+	if (mapping == NULL)
+		mapping = &sdp->sd_aspace;
+
 	shift = PAGE_CACHE_SHIFT - sdp->sd_sb.sb_bsize_shift;
 	index = blkno >> shift;             /* convert block to page */
 	bufnum = blkno - (index << shift);  /* block buf index within page */

fs/gfs2/ops_fstype.c

@@ -36,6 +36,7 @@
 #include "log.h"
 #include "quota.h"
 #include "dir.h"
+#include "meta_io.h"
 #include "trace_gfs2.h"
 
 #define DO 0
@@ -62,6 +63,7 @@ static void gfs2_tune_init(struct gfs2_tune *gt)
 static struct gfs2_sbd *init_sbd(struct super_block *sb)
 {
 	struct gfs2_sbd *sdp;
+	struct address_space *mapping;
 
 	sdp = kzalloc(sizeof(struct gfs2_sbd), GFP_KERNEL);
 	if (!sdp)
@@ -98,6 +100,16 @@ static struct gfs2_sbd *init_sbd(struct super_block *sb)
 	INIT_LIST_HEAD(&sdp->sd_trunc_list);
 	spin_lock_init(&sdp->sd_trunc_lock);
 
+	mapping = &sdp->sd_aspace;
+
+	mapping->a_ops = &gfs2_meta_aops;
+	mapping->host = sb->s_bdev->bd_inode;
+	mapping->flags = 0;
+	mapping_set_gfp_mask(mapping, GFP_NOFS);
+	mapping->private_data = NULL;
+	mapping->backing_dev_info = sb->s_bdi;
+	mapping->writeback_index = 0;
+
 	spin_lock_init(&sdp->sd_log_lock);
 	atomic_set(&sdp->sd_log_pinned, 0);
 	INIT_LIST_HEAD(&sdp->sd_log_le_buf);