[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, 4 insertions, 2 deletions

diff --git a/fs/gfs2/ops_file.c b/fs/gfs2/ops_file.c
index 597f7ff..d7f4726 100644
--- a/fs/gfs2/ops_file.c
+++ b/fs/gfs2/ops_file.c
@@ -364,9 +364,11 @@ static int gfs2_page_mkwrite(struct vm_area_struct *vma, struct page *page)
 	ret = gfs2_write_alloc_required(ip, pos, PAGE_CACHE_SIZE, &alloc_required);
 	if (ret || !alloc_required)
 		goto out_unlock;
-
-	ip->i_alloc.al_requested = 0;
+	ret = -ENOMEM;
 	al = gfs2_alloc_get(ip);
+	if (al == NULL)
+		goto out_unlock;
+
 	ret = gfs2_quota_lock(ip, NO_QUOTA_CHANGE, NO_QUOTA_CHANGE);
 	if (ret)
 		goto out_alloc_put;