| Message ID | 20180905215816.4779-1-richard.weiyang@gmail.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | KVM: x86: adjust kvm_mmu_page member to save 8 bytes | expand |
On 05/09/2018 23:58, Wei Yang wrote: > On a 64bits machine, struct is naturally aligned with 8 bytes. Since > kvm_mmu_page member *unsync* and *role* are less then 4 bytes, we can > rearrange the sequence to compace the struct. > > As the comment shows, *role* and *gfn* are used to key the shadow page. In > order to keep the comment valid, this patch moves the *unsync* up and > exchange the position of *role* and *gfn*. > > From /proc/slabinfo, it shows the size of kvm_mmu_page is 8 bytes less and > with one more object per slap after applying this patch. > > # name <active_objs> <num_objs> <objsize> <objperslab> > kvm_mmu_page_header 0 0 168 24 > > kvm_mmu_page_header 0 0 160 25 > > Signed-off-by: Wei Yang <richard.weiyang@gmail.com> > --- > arch/x86/include/asm/kvm_host.h | 4 ++-- > 1 file changed, 2 insertions(+), 2 deletions(-) > > diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h > index 00ddb0c9e612..f1a4e520ef5c 100644 > --- a/arch/x86/include/asm/kvm_host.h > +++ b/arch/x86/include/asm/kvm_host.h > @@ -280,18 +280,18 @@ struct kvm_rmap_head { > struct kvm_mmu_page { > struct list_head link; > struct hlist_node hash_link; > + bool unsync; > > /* > * The following two entries are used to key the shadow page in the > * hash table. > */ > - gfn_t gfn; > union kvm_mmu_page_role role; > + gfn_t gfn; > > u64 *spt; > /* hold the gfn of each spte inside spt */ > gfn_t *gfns; > - bool unsync; > int root_count; /* Currently serving as active root */ > unsigned int unsync_children; > struct kvm_rmap_head parent_ptes; /* rmap pointers to parent sptes */ > Queued, thanks. Paolo
diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h index 00ddb0c9e612..f1a4e520ef5c 100644 --- a/arch/x86/include/asm/kvm_host.h +++ b/arch/x86/include/asm/kvm_host.h @@ -280,18 +280,18 @@ struct kvm_rmap_head { struct kvm_mmu_page { struct list_head link; struct hlist_node hash_link; + bool unsync; /* * The following two entries are used to key the shadow page in the * hash table. */ - gfn_t gfn; union kvm_mmu_page_role role; + gfn_t gfn; u64 *spt; /* hold the gfn of each spte inside spt */ gfn_t *gfns; - bool unsync; int root_count; /* Currently serving as active root */ unsigned int unsync_children; struct kvm_rmap_head parent_ptes; /* rmap pointers to parent sptes */
On a 64bits machine, struct is naturally aligned with 8 bytes. Since kvm_mmu_page member *unsync* and *role* are less then 4 bytes, we can rearrange the sequence to compace the struct. As the comment shows, *role* and *gfn* are used to key the shadow page. In order to keep the comment valid, this patch moves the *unsync* up and exchange the position of *role* and *gfn*. From /proc/slabinfo, it shows the size of kvm_mmu_page is 8 bytes less and with one more object per slap after applying this patch. # name <active_objs> <num_objs> <objsize> <objperslab> kvm_mmu_page_header 0 0 168 24 kvm_mmu_page_header 0 0 160 25 Signed-off-by: Wei Yang <richard.weiyang@gmail.com> --- arch/x86/include/asm/kvm_host.h | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-)