| Message ID | 559c9a70419846e0cfc319505d3d5fffd45b3358.1682618727.git.christophe.jaillet@wanadoo.fr |
|---|---|
| State | New |
| Headers | show |
| Series | ceph: Reorder fields in 'struct ceph_snapid_map' | expand |
On 4/28/23 02:05, Christophe JAILLET wrote: > Group some variables based on their sizes to reduce holes. > On x86_64, this shrinks the size of 'struct ceph_snapid_map' from 72 to 64 > bytes. > > When such a structure is allocated, because of the way memory allocation > works, when 72 bytes were requested, 96 bytes were allocated. > > So, on x86_64, this change saves 32 bytes per allocation and has the > structure fit in a single cacheline. > > Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr> > --- > Using pahole > > Before: > ====== > struct ceph_snapid_map { > struct rb_node node __attribute__((__aligned__(8))); /* 0 24 */ > struct list_head lru; /* 24 16 */ > atomic_t ref; /* 40 4 */ > > /* XXX 4 bytes hole, try to pack */ > > u64 snap; /* 48 8 */ > dev_t dev; /* 56 4 */ > > /* XXX 4 bytes hole, try to pack */ > > /* --- cacheline 1 boundary (64 bytes) --- */ > long unsigned int last_used; /* 64 8 */ > > /* size: 72, cachelines: 2, members: 6 */ > /* sum members: 64, holes: 2, sum holes: 8 */ > /* forced alignments: 1 */ > /* last cacheline: 8 bytes */ > } __attribute__((__aligned__(8))); > --- > fs/ceph/mds_client.h | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/fs/ceph/mds_client.h b/fs/ceph/mds_client.h > index 0598faa50e2e..2328dbda5ab6 100644 > --- a/fs/ceph/mds_client.h > +++ b/fs/ceph/mds_client.h > @@ -355,8 +355,8 @@ struct ceph_snapid_map { > struct rb_node node; > struct list_head lru; > atomic_t ref; > - u64 snap; > dev_t dev; > + u64 snap; > unsigned long last_used; > }; > This looks good to me. Thanks. Will apply it to the testing branch. - Xiubo
On Fri, 2023-04-28 at 08:53 +0800, Xiubo Li wrote: > On 4/28/23 02:05, Christophe JAILLET wrote: > > Group some variables based on their sizes to reduce holes. > > On x86_64, this shrinks the size of 'struct ceph_snapid_map' from 72 to 64 > > bytes. > > > > When such a structure is allocated, because of the way memory allocation > > works, when 72 bytes were requested, 96 bytes were allocated. > > > > So, on x86_64, this change saves 32 bytes per allocation and has the > > structure fit in a single cacheline. > > > > Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr> > > --- > > Using pahole > > > > Before: > > ====== > > struct ceph_snapid_map { > > struct rb_node node __attribute__((__aligned__(8))); /* 0 24 */ > > struct list_head lru; /* 24 16 */ > > atomic_t ref; /* 40 4 */ > > > > /* XXX 4 bytes hole, try to pack */ > > > > u64 snap; /* 48 8 */ > > dev_t dev; /* 56 4 */ > > > > /* XXX 4 bytes hole, try to pack */ > > > > /* --- cacheline 1 boundary (64 bytes) --- */ > > long unsigned int last_used; /* 64 8 */ > > > > /* size: 72, cachelines: 2, members: 6 */ > > /* sum members: 64, holes: 2, sum holes: 8 */ > > /* forced alignments: 1 */ > > /* last cacheline: 8 bytes */ > > } __attribute__((__aligned__(8))); > > --- > > fs/ceph/mds_client.h | 2 +- > > 1 file changed, 1 insertion(+), 1 deletion(-) > > > > diff --git a/fs/ceph/mds_client.h b/fs/ceph/mds_client.h > > index 0598faa50e2e..2328dbda5ab6 100644 > > --- a/fs/ceph/mds_client.h > > +++ b/fs/ceph/mds_client.h > > @@ -355,8 +355,8 @@ struct ceph_snapid_map { > > struct rb_node node; > > struct list_head lru; > > atomic_t ref; > > - u64 snap; > > dev_t dev; > > + u64 snap; > > unsigned long last_used; > > }; > > > > This looks good to me. Thanks. > > Will apply it to the testing branch. > > - Xiubo > > > Reviewed-by: Jeff Layton <jlayton@kernel.org>
diff --git a/fs/ceph/mds_client.h b/fs/ceph/mds_client.h index 0598faa50e2e..2328dbda5ab6 100644 --- a/fs/ceph/mds_client.h +++ b/fs/ceph/mds_client.h @@ -355,8 +355,8 @@ struct ceph_snapid_map { struct rb_node node; struct list_head lru; atomic_t ref; - u64 snap; dev_t dev; + u64 snap; unsigned long last_used; };
Group some variables based on their sizes to reduce holes. On x86_64, this shrinks the size of 'struct ceph_snapid_map' from 72 to 64 bytes. When such a structure is allocated, because of the way memory allocation works, when 72 bytes were requested, 96 bytes were allocated. So, on x86_64, this change saves 32 bytes per allocation and has the structure fit in a single cacheline. Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr> --- Using pahole Before: ====== struct ceph_snapid_map { struct rb_node node __attribute__((__aligned__(8))); /* 0 24 */ struct list_head lru; /* 24 16 */ atomic_t ref; /* 40 4 */ /* XXX 4 bytes hole, try to pack */ u64 snap; /* 48 8 */ dev_t dev; /* 56 4 */ /* XXX 4 bytes hole, try to pack */ /* --- cacheline 1 boundary (64 bytes) --- */ long unsigned int last_used; /* 64 8 */ /* size: 72, cachelines: 2, members: 6 */ /* sum members: 64, holes: 2, sum holes: 8 */ /* forced alignments: 1 */ /* last cacheline: 8 bytes */ } __attribute__((__aligned__(8))); --- fs/ceph/mds_client.h | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)