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KVM: x86: adjust kvm_mmu_page member to save 8 bytes 

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>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
hifive-unleashed-5.1
Wei Yang 2018-09-06 05:58:16 +08:00 committed by Paolo Bonzini
parent bd18bffca3
commit 3ff519f29d
1 changed files with 2 additions and 2 deletions
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4
arch/x86/include/asm/kvm_host.h
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@ -281,18 +281,18 @@ 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 */