[PATCH 2/2] KVM: MMU: Recover space used by rcu_head in struct kvm_mmu_page

[Avi Kivity <avi@redhat.com>]

By overlaying the field with 'link', we reduce the structure size by
16 bytes.

Changing call_rcu() to be per-page is not strictly necessary, but it
can help RCU estimate the amount of work pending.

Signed-off-by: Avi Kivity <avi@redhat.com>
---
 arch/x86/include/asm/kvm_host.h |    7 ++++---
 arch/x86/kvm/mmu.c              |   26 +++++++++-----------------
 2 files changed, 13 insertions(+), 20 deletions(-)

diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index b885445..ae02ff8 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -208,7 +208,10 @@ union kvm_mmu_page_role {
 };
 
 struct kvm_mmu_page {
-	struct list_head link;
+	union {
+		struct list_head link;
+		struct rcu_head rcu;
+	};
 	struct hlist_node hash_link;
 
 	/*
@@ -237,8 +240,6 @@ struct kvm_mmu_page {
 #endif
 
 	int write_flooding_count;
-
-	struct rcu_head rcu;
 };
 
 struct kvm_pio_request {
diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c
index c10f60b..26257d7 100644
--- a/arch/x86/kvm/mmu.c
+++ b/arch/x86/kvm/mmu.c
@@ -1338,7 +1338,6 @@ static void kvm_mmu_isolate_page(struct kvm_mmu_page *sp)
  */
 static void kvm_mmu_free_page(struct kvm_mmu_page *sp)
 {
-	list_del(&sp->link);
 	free_page((unsigned long)sp->spt);
 	kmem_cache_free(mmu_page_header_cache, sp);
 }
@@ -1980,20 +1979,12 @@ static void kvm_mmu_isolate_pages(struct list_head *invalid_list)
 		kvm_mmu_isolate_page(sp);
 }
 
-static void free_pages_rcu(struct rcu_head *head)
+static void free_page_rcu(struct rcu_head *head)
 {
-	struct kvm_mmu_page *next, *sp;
+	struct kvm_mmu_page *sp;
 
 	sp = container_of(head, struct kvm_mmu_page, rcu);
-	while (sp) {
-		if (!list_empty(&sp->link))
-			next = list_first_entry(&sp->link,
-				      struct kvm_mmu_page, link);
-		else
-			next = NULL;
-		kvm_mmu_free_page(sp);
-		sp = next;
-	}
+	kvm_mmu_free_page(sp);
 }
 
 static void kvm_mmu_commit_zap_page(struct kvm *kvm,
@@ -2007,11 +1998,12 @@ static void kvm_mmu_commit_zap_page(struct kvm *kvm,
 	kvm_flush_remote_tlbs(kvm);
 
 	kvm_mmu_isolate_pages(invalid_list);
-	sp = list_first_entry(invalid_list, struct kvm_mmu_page, link);
-	list_del_init(invalid_list);
-
-	trace_kvm_mmu_delay_free_pages(sp);
-	call_rcu(&sp->rcu, free_pages_rcu);
+	while (!list_empty(invalid_list)) {
+		sp = list_first_entry(invalid_list, struct kvm_mmu_page, link);
+		list_del(&sp->link);
+		trace_kvm_mmu_delay_free_pages(sp);
+		call_rcu(&sp->rcu, free_page_rcu);
+	}
 }
 
 /*
-- 
1.7.10