[GFS2] Reduce inode size by moving i_alloc out of line

It is possible to reduce the size of GFS2 inodes by taking the i_alloc
structure out of the gfs2_inode. This patch allocates the i_alloc
structure whenever its needed, and frees it afterward. This decreases
the amount of low memory we use at the expense of requiring a memory
allocation for each page or partial page that we write. A quick test
with postmark shows that the overhead is not measurable and I also note
that OCFS2 use the same approach.

In the future I'd like to solve the problem by shrinking down the size
of the members of the i_alloc structure, but for now, this reduces the
immediate problem of using too much low-memory on x86 and doesn't add
too much overhead.

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 745dada4085c..4cdda1a3e12c 100644
--- a/fs/gfs2/incore.h
+++ b/fs/gfs2/incore.h
@@ -264,7 +264,7 @@ struct gfs2_inode {
         struct gfs2_glock *i_gl; /* Move into i_gh? */
         struct gfs2_holder i_iopen_gh;
         struct gfs2_holder i_gh; /* for prepare/commit_write only */
-        struct gfs2_alloc i_alloc;
+        struct gfs2_alloc *i_alloc;
         u64 i_last_rg_alloc;
 
         spinlock_t i_spin;