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

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

[Andreas Gruenbacher]

As per a suggestion by Linus, don't pack struct lm_lockname: we did that
because the struct 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>
---
 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 ec0848f..903c853 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) &&	\
-- 
2.7.4

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

[Andrew Price]

On 15/03/17 18:48, Andreas Gruenbacher wrote:
> As per a suggestion by Linus, don't pack struct lm_lockname: we did that
> because the struct 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>

Tested-by: Andrew Price <anprice@redhat.com>

Andy

> ---
>  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 ec0848f..903c853 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) &&	\
>

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

[Bob Peterson]

----- Original Message -----
| As per a suggestion by Linus, don't pack struct lm_lockname: we did that
| because the struct 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>
| ---

Hi,

Thanks. This is now applied to the for-next branch of the linux-gfs2 tree:
https://git.kernel.org/pub/scm/linux/kernel/git/gfs2/linux-gfs2.git/commit/?h=for-next&id=972b044eeca582ef173d063773e292bd9e8633d6

Regards,

Bob Peterson
Red Hat File Systems