GFS2: Use rbtree for resource groups and clean up bitmap buffer ref count scheme

Here is an update of Bob's original rbtree patch which, in addition, also
resolves the rather strange ref counting that was being done relating to
the bitmap blocks.

Originally we had a dual system for journaling resource groups. The metadata
blocks were journaled and also the rgrp itself was added to a list. The reason
for adding the rgrp to the list in the journal was so that the "repolish
clones" code could be run to update the free space, and potentially send any
discard requests when the log was flushed. This was done by comparing the
"cloned" bitmap with what had been written back on disk during the transaction
commit.

Due to this, there was a requirement to hang on to the rgrps' bitmap buffers
until the journal had been flushed. For that reason, there was a rather
complicated set up in the ->go_lock ->go_unlock functions for rgrps involving
both a mutex and a spinlock (the ->sd_rindex_spin) to maintain a reference
count on the buffers.

However, the journal maintains a reference count on the buffers anyway, since
they are being journaled as metadata buffers. So by moving the code which deals
with the post-journal accounting for bitmap blocks to the metadata journaling
code, we can entirely dispense with the rather strange buffer ref counting
scheme and also the requirement to journal the rgrps.

The net result of all this is that the ->sd_rindex_spin is left to do exactly
one job, and that is to look after the rbtree or rgrps.

This patch is designed to be a stepping stone towards using RCU for the rbtree
of resource groups, however the reduction in the number of uses of the
->sd_rindex_spin is likely to have benefits for multi-threaded workloads,
anyway.

The patch retains ->go_lock and ->go_unlock for rgrps, however these maybe also
be removed in future in favour of calling the functions directly where required
in the code. That will allow locking of resource groups without needing to
actually read them in - something that could be useful in speeding up statfs.

In the mean time though it is valid to dereference ->bi_bh only when the rgrp
is locked. This is basically the same rule as before, modulo the references not
being valid until the following journal flush.

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

1 files changed, 3 insertions, 8 deletions

diff --git a/fs/gfs2/incore.h b/fs/gfs2/incore.h
index be5801a75406..9e753fc9e6a5 100644
--- a/fs/gfs2/incore.h
+++ b/fs/gfs2/incore.h
@@ -18,6 +18,7 @@
 #include <linux/rcupdate.h>
 #include <linux/rculist_bl.h>
 #include <linux/completion.h>
+#include <linux/rbtree.h>
 
 #define DIO_WAIT	0x00000010
 #define DIO_METADATA	0x00000020
@@ -78,8 +79,7 @@ struct gfs2_bitmap {
 };
 
 struct gfs2_rgrpd {
-	struct list_head rd_list;	/* Link with superblock */
-	struct list_head rd_list_mru;
+	struct rb_node rd_node;		/* Link with superblock */
 	struct gfs2_glock *rd_gl;	/* Glock for this rgrp */
 	u64 rd_addr;			/* grp block disk address */
 	u64 rd_data0;			/* first data location */
@@ -91,10 +91,7 @@ struct gfs2_rgrpd {
 	u32 rd_dinodes;
 	u64 rd_igeneration;
 	struct gfs2_bitmap *rd_bits;
-	struct mutex rd_mutex;
-	struct gfs2_log_element rd_le;
 	struct gfs2_sbd *rd_sbd;
-	unsigned int rd_bh_count;
 	u32 rd_last_alloc;
 	u32 rd_flags;
 #define GFS2_RDF_CHECK		0x10000000 /* check for unlinked inodes */
@@ -575,9 +572,7 @@ struct gfs2_sbd {
 	int sd_rindex_uptodate;
 	spinlock_t sd_rindex_spin;
 	struct mutex sd_rindex_mutex;
-	struct list_head sd_rindex_list;
-	struct list_head sd_rindex_mru_list;
-	struct gfs2_rgrpd *sd_rindex_forward;
+	struct rb_root sd_rindex_tree;
 	unsigned int sd_rgrps;
 	unsigned int sd_max_rg_data;