[Cluster-devel] [PATCH 4/9] gfs2: Don't pack struct lm_lockname

[Bob Peterson <rpeterso@redhat.com>]

From: Andreas Gruenbacher <agruenba@redhat.com>

As per a suggestion by Linus, don't pack struct lm_lockname: we did that
because the struct is used as a rhashtable key, but packing tells the
compiler that the 64-bit fields in the struct may be unaligned, causing
it to generate worse code on some architectures.  Instead, rearrange the
fields in the struct so that there is no padding between fields, and
exclude any tail padding from the hash key size.

Signed-off-by: Andreas Gruenbacher <agruenba@redhat.com>
Signed-off-by: Bob Peterson <rpeterso@redhat.com>
---
 fs/gfs2/glock.c  | 2 +-
 fs/gfs2/incore.h | 8 ++++++--
 2 files changed, 7 insertions(+), 3 deletions(-)

diff --git a/fs/gfs2/glock.c b/fs/gfs2/glock.c
index b2638d8..35f3b0a 100644
--- a/fs/gfs2/glock.c
+++ b/fs/gfs2/glock.c
@@ -73,7 +73,7 @@ static DEFINE_SPINLOCK(lru_lock);
 
 static struct rhashtable_params ht_parms = {
 	.nelem_hint = GFS2_GL_HASH_SIZE * 3 / 4,
-	.key_len = sizeof(struct lm_lockname),
+	.key_len = offsetofend(struct lm_lockname, ln_type),
 	.key_offset = offsetof(struct gfs2_glock, gl_name),
 	.head_offset = offsetof(struct gfs2_glock, gl_node),
 };
diff --git a/fs/gfs2/incore.h b/fs/gfs2/incore.h
index 511e1ed..b7cf65d 100644
--- a/fs/gfs2/incore.h
+++ b/fs/gfs2/incore.h
@@ -203,11 +203,15 @@ enum {
 	DFL_DLM_RECOVERY	= 6,
 };
 
+/*
+ * We are using struct lm_lockname as an rhashtable key.  Avoid holes within
+ * the struct; padding at the end is fine.
+ */
 struct lm_lockname {
-	struct gfs2_sbd *ln_sbd;
 	u64 ln_number;
+	struct gfs2_sbd *ln_sbd;
 	unsigned int ln_type;
-} __packed __aligned(sizeof(int));
+};
 
 #define lm_name_equal(name1, name2) \
         (((name1)->ln_number == (name2)->ln_number) &&	\
-- 
2.9.3