[GFS2] Shrink gfs2_inode memory by half

Here is something I spotted (while looking for something entirely
different) the other day.

Rather than using a completion in each and every struct gfs2_holder,
this removes it in favour of hashed wait queues, thus saving a
considerable amount of memory both on the stack (where a number of
gfs2_holder structures are allocated) and in particular in the
gfs2_inode which has 8 gfs2_holder structures embedded within it.

As a result on x86_64 the gfs2_inode shrinks from 2488 bytes to
1912 bytes, a saving of 576 bytes per inode (no thats not a typo!).
In actual practice we get a much better result than that since
now that a gfs2_inode is under the 2048 byte barrier, we get two
per 4k slab page effectively halving the amount of memory required
to store gfs2_inodes.

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

1 files changed, 1 insertions, 1 deletions

diff --git a/fs/gfs2/incore.h b/fs/gfs2/incore.h
index 9114851ac53e..a24c4af09ce0 100644
--- a/fs/gfs2/incore.h
+++ b/fs/gfs2/incore.h
@@ -128,6 +128,7 @@ enum {
         HIF_HOLDER              = 6,
         HIF_FIRST               = 7,
         HIF_ABORTED             = 9,
+        HIF_WAIT                = 10,
 };
 
 struct gfs2_holder {
@@ -140,7 +141,6 @@ struct gfs2_holder {
 
         int gh_error;
         unsigned long gh_iflags;
-        struct completion gh_wait;
         unsigned long gh_ip;
 };