[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, 9 insertions, 11 deletions

diff --git a/fs/gfs2/rgrp.c b/fs/gfs2/rgrp.c
index 68c4bf363c46..3552110b2e5f 100644
--- a/fs/gfs2/rgrp.c
+++ b/fs/gfs2/rgrp.c
@@ -819,11 +819,9 @@ void gfs2_rgrp_repolish_clones(struct gfs2_rgrpd *rgd)
 
 struct gfs2_alloc *gfs2_alloc_get(struct gfs2_inode *ip)
 {
-        struct gfs2_alloc *al = &ip->i_alloc;
-
-        /* FIXME: Should assert that the correct locks are held here... */
-        memset(al, 0, sizeof(*al));
-        return al;
+        BUG_ON(ip->i_alloc != NULL);
+        ip->i_alloc = kzalloc(sizeof(struct gfs2_alloc), GFP_KERNEL);
+        return ip->i_alloc;
 }
 
 /**
@@ -1061,7 +1059,7 @@ static struct inode *get_local_rgrp(struct gfs2_inode *ip, u64 *last_unlinked)
         struct inode *inode = NULL;
         struct gfs2_sbd *sdp = GFS2_SB(&ip->i_inode);
         struct gfs2_rgrpd *rgd, *begin = NULL;
-        struct gfs2_alloc *al = &ip->i_alloc;
+        struct gfs2_alloc *al = ip->i_alloc;
         int flags = LM_FLAG_TRY;
         int skipped = 0;
         int loops = 0;
@@ -1176,7 +1174,7 @@ out:
 int gfs2_inplace_reserve_i(struct gfs2_inode *ip, char *file, unsigned int line)
 {
         struct gfs2_sbd *sdp = GFS2_SB(&ip->i_inode);
-        struct gfs2_alloc *al = &ip->i_alloc;
+        struct gfs2_alloc *al = ip->i_alloc;
         struct inode *inode;
         int error = 0;
         u64 last_unlinked = NO_BLOCK;
@@ -1222,7 +1220,7 @@ try_again:
 void gfs2_inplace_release(struct gfs2_inode *ip)
 {
         struct gfs2_sbd *sdp = GFS2_SB(&ip->i_inode);
-        struct gfs2_alloc *al = &ip->i_alloc;
+        struct gfs2_alloc *al = ip->i_alloc;
 
         if (gfs2_assert_warn(sdp, al->al_alloced <= al->al_requested) == -1)
                 fs_warn(sdp, "al_alloced = %u, al_requested = %u "
@@ -1412,7 +1410,7 @@ static struct gfs2_rgrpd *rgblk_free(struct gfs2_sbd *sdp, u64 bstart,
 u64 gfs2_alloc_data(struct gfs2_inode *ip)
 {
         struct gfs2_sbd *sdp = GFS2_SB(&ip->i_inode);
-        struct gfs2_alloc *al = &ip->i_alloc;
+        struct gfs2_alloc *al = ip->i_alloc;
         struct gfs2_rgrpd *rgd = al->al_rgd;
         u32 goal, blk;
         u64 block;
@@ -1457,7 +1455,7 @@ u64 gfs2_alloc_data(struct gfs2_inode *ip)
 u64 gfs2_alloc_meta(struct gfs2_inode *ip)
 {
         struct gfs2_sbd *sdp = GFS2_SB(&ip->i_inode);
-        struct gfs2_alloc *al = &ip->i_alloc;
+        struct gfs2_alloc *al = ip->i_alloc;
         struct gfs2_rgrpd *rgd = al->al_rgd;
         u32 goal, blk;
         u64 block;
@@ -1503,7 +1501,7 @@ u64 gfs2_alloc_meta(struct gfs2_inode *ip)
 u64 gfs2_alloc_di(struct gfs2_inode *dip, u64 *generation)
 {
         struct gfs2_sbd *sdp = GFS2_SB(&dip->i_inode);
-        struct gfs2_alloc *al = &dip->i_alloc;
+        struct gfs2_alloc *al = dip->i_alloc;
         struct gfs2_rgrpd *rgd = al->al_rgd;
         u32 blk;
         u64 block;