[Xen-devel] [Linux PATCH] Mark hugepages to the hypervisor to speed up mapping (with signoff this time)

[Dave McCracken <dcm@xxxxxxxx>]

Two new hypercalls were recently added to the Xen hypervisor to mark
and unmark hugepages as in use.  Once a hugepage has been marked,
actually mapping the hugepage is sped up by a significant amount (more
than 20 times faster).

This patch marks hugepages when they are added to the hugepage pool
and unmarks them when they are removed.  It also checks to make sure
each hugepage is contiguous at the machine level.

Signed-off-by: Dave McCracken <dave.mccracken@xxxxxxxxxx>

--------


--- next/arch/x86/xen/mmu.c     2010-06-01 11:41:54.000000000 -0500
+++ next-fh//arch/x86/xen/mmu.c 2010-06-02 08:45:01.000000000 -0500
@@ -2531,3 +2531,51 @@ static int __init xen_mmu_debugfs(void)
 fs_initcall(xen_mmu_debugfs);
 
 #endif /* CONFIG_XEN_DEBUG_FS */
+
+static int mark_ok = 1;
+
+int arch_prepare_hugepage(struct page *page)
+{
+       struct mmuext_op op;
+       unsigned long pfn, mfn, m;
+       int i;
+       int rc;
+
+       pfn = page_to_pfn(page);
+       mfn = pfn_to_mfn(pfn);
+       if (mfn & ((HPAGE_SIZE/PAGE_SIZE)-1)) {
+               printk("Guest pages are not properly aligned to use 
hugepages\n");
+               return 1;
+       }
+       for (i = 0, m = mfn; i < HPAGE_SIZE/PAGE_SIZE; i++, pfn++, m++) {
+               if (pfn_to_mfn(pfn) != m) {
+                       printk("Guest pages are not properly aligned to use 
hugepages\n");
+                       return 1;
+               }
+       }
+       /* It's ok if this fails.  We just fall back to the slow refcounting */
+       if (mark_ok) {
+               op.cmd = MMUEXT_MARK_SUPER;
+               op.arg1.mfn = mfn;
+               rc = HYPERVISOR_mmuext_op(&op, 1, NULL, DOMID_SELF);
+               if (rc) {
+                       if (rc == -ENOSYS) {
+                               mark_ok = 0;
+                               return 0;
+                       }
+                       return 1;
+               }
+       }
+       return 0;
+}
+
+void arch_release_hugepage(struct page *page)
+{
+       struct mmuext_op op;
+
+       if (mark_ok) {
+               op.cmd = MMUEXT_UNMARK_SUPER;
+               op.arg1.mfn = pfn_to_mfn(page_to_pfn(page));
+               HYPERVISOR_mmuext_op(&op, 1, NULL, DOMID_SELF);
+       }
+}
--- next/arch/x86/include/asm/hugetlb.h 2010-06-01 11:41:54.000000000 -0500
+++ next-fh//arch/x86/include/asm/hugetlb.h     2010-06-02 08:37:58.000000000 
-0500
@@ -95,6 +95,10 @@ static inline int huge_ptep_set_access_f
        return changed;
 }
 
+#ifdef CONFIG_XEN
+int arch_prepare_hugepage(struct page *page);
+void arch_release_hugepage(struct page *page);
+#else
 static inline int arch_prepare_hugepage(struct page *page)
 {
        return 0;
@@ -103,5 +107,6 @@ static inline int arch_prepare_hugepage(
 static inline void arch_release_hugepage(struct page *page)
 {
 }
+#endif
 
 #endif /* _ASM_X86_HUGETLB_H */
--- next/include/xen/interface/xen.h    2010-06-01 11:41:59.000000000 -0500
+++ next-fh//include/xen/interface/xen.h        2010-06-02 08:38:50.000000000 
-0500
@@ -167,6 +167,19 @@
  * cmd: MMUEXT_SET_LDT
  * linear_addr: Linear address of LDT base (NB. must be page-aligned).
  * nr_ents: Number of entries in LDT.
+ *
+ * cmd: MMUEXT_CLEAR_PAGE
+ * mfn: Machine frame number to be cleared.
+ *
+ * cmd: MMUEXT_COPY_PAGE
+ * mfn: Machine frame number of the destination page.
+ * src_mfn: Machine frame number of the source page.
+ *
+ * cmd: MMUEXT_MARK_SUPER
+ * mfn: Machine frame number of head of superpage to be marked.
+ *
+ * cmd: MMUEXT_UNMARK_SUPER
+ * mfn: Machine frame number of head of superpage to be cleared.
  */
 #define MMUEXT_PIN_L1_TABLE      0
 #define MMUEXT_PIN_L2_TABLE      1
@@ -183,6 +196,10 @@
 #define MMUEXT_FLUSH_CACHE      12
 #define MMUEXT_SET_LDT          13
 #define MMUEXT_NEW_USER_BASEPTR 15
+#define MMUEXT_CLEAR_PAGE       16
+#define MMUEXT_COPY_PAGE        17
+#define MMUEXT_MARK_SUPER       19
+#define MMUEXT_UNMARK_SUPER     20
 
 #ifndef __ASSEMBLY__
 #include <linux/types.h>

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