[Xen-devel] [PATCH] linux/i386: allow CONFIG_HIGHPTE on i386

["Jan Beulich" <jbeulich@xxxxxxxxxx>]

While, as discussed, the performance impact of this option is certainly higher
than on native Linux, the option should not be entirely disallowed if people
want to sacrifice performance for less lowmem pressure.

The patch at once does away with the use of PageForeign on pte pages, to match
x86-64 and to reduce the delta to native.

Signed-off-by: Jan Beulich <jbeulich@xxxxxxxxxx>

Index: sle10-sp1-2006-12-21/arch/i386/Kconfig
===================================================================
--- sle10-sp1-2006-12-21.orig/arch/i386/Kconfig 2007-01-09 14:39:13.000000000 
+0100
+++ sle10-sp1-2006-12-21/arch/i386/Kconfig      2007-01-09 11:47:18.000000000 
+0100
@@ -594,7 +594,7 @@ config HAVE_ARCH_EARLY_PFN_TO_NID
 
 config HIGHPTE
        bool "Allocate 3rd-level pagetables from highmem"
-       depends on (HIGHMEM4G || HIGHMEM64G) && !X86_XEN
+       depends on HIGHMEM4G || HIGHMEM64G
        help
          The VM uses one page table entry for each page of physical memory.
          For systems with a lot of RAM, this can be wasteful of precious
Index: sle10-sp1-2006-12-21/arch/i386/mm/highmem-xen.c
===================================================================
--- sle10-sp1-2006-12-21.orig/arch/i386/mm/highmem-xen.c        2007-01-09 
14:39:13.000000000 +0100
+++ sle10-sp1-2006-12-21/arch/i386/mm/highmem-xen.c     2007-01-09 
12:45:43.000000000 +0100
@@ -129,5 +129,6 @@ struct page *kmap_atomic_to_page(void *p
 EXPORT_SYMBOL(kmap);
 EXPORT_SYMBOL(kunmap);
 EXPORT_SYMBOL(kmap_atomic);
+EXPORT_SYMBOL(kmap_atomic_pte);
 EXPORT_SYMBOL(kunmap_atomic);
 EXPORT_SYMBOL(kmap_atomic_to_page);
Index: sle10-sp1-2006-12-21/arch/i386/mm/pgtable-xen.c
===================================================================
--- sle10-sp1-2006-12-21.orig/arch/i386/mm/pgtable-xen.c        2007-01-09 
14:39:13.000000000 +0100
+++ sle10-sp1-2006-12-21/arch/i386/mm/pgtable-xen.c     2007-01-09 
16:53:58.000000000 +0100
@@ -238,26 +238,37 @@ struct page *pte_alloc_one(struct mm_str
 
 #ifdef CONFIG_HIGHPTE
        pte = alloc_pages(GFP_KERNEL|__GFP_HIGHMEM|__GFP_REPEAT|__GFP_ZERO, 0);
+       if (pte && PageHighMem(pte)) {
+               struct mmuext_op op;
+
+               kmap_flush_unused();
+               op.cmd = MMUEXT_PIN_L1_TABLE;
+               op.arg1.mfn = pfn_to_mfn(page_to_pfn(pte));
+               BUG_ON(HYPERVISOR_mmuext_op(&op, 1, NULL, DOMID_SELF) < 0);
+       }
 #else
        pte = alloc_pages(GFP_KERNEL|__GFP_REPEAT|__GFP_ZERO, 0);
-       if (pte) {
-               SetPageForeign(pte, pte_free);
-               set_page_count(pte, 1);
-       }
 #endif
        return pte;
 }
 
 void pte_free(struct page *pte)
 {
-       unsigned long va = (unsigned long)__va(page_to_pfn(pte)<<PAGE_SHIFT);
+       unsigned long pfn = page_to_pfn(pte);
 
-       if (!pte_write(*virt_to_ptep(va)))
-               BUG_ON(HYPERVISOR_update_va_mapping(
-                       va, pfn_pte(page_to_pfn(pte), PAGE_KERNEL), 0));
+       if (!PageHighMem(pte)) {
+               unsigned long va = (unsigned long)__va(pfn << PAGE_SHIFT);
 
-       ClearPageForeign(pte);
-       set_page_count(pte, 1);
+               if (!pte_write(*virt_to_ptep(va)))
+                       BUG_ON(HYPERVISOR_update_va_mapping(
+                              va, pfn_pte(pfn, PAGE_KERNEL), 0));
+       } else {
+               struct mmuext_op op;
+
+               op.cmd = MMUEXT_UNPIN_TABLE;
+               op.arg1.mfn = pfn_to_mfn(pfn);
+               BUG_ON(HYPERVISOR_mmuext_op(&op, 1, NULL, DOMID_SELF) < 0);
+       }
 
        __free_page(pte);
 }
Index: sle10-sp1-2006-12-21/include/asm-i386/mach-xen/asm/pgalloc.h
===================================================================
--- sle10-sp1-2006-12-21.orig/include/asm-i386/mach-xen/asm/pgalloc.h   
2007-01-09 14:39:13.000000000 +0100
+++ sle10-sp1-2006-12-21/include/asm-i386/mach-xen/asm/pgalloc.h        
2007-01-09 11:11:54.000000000 +0100
@@ -42,12 +42,12 @@ extern struct page *pte_alloc_one(struct
 static inline void pte_free_kernel(pte_t *pte)
 {
        free_page((unsigned long)pte);
-       make_page_writable(pte, XENFEAT_writable_page_tables);
+       make_lowmem_page_writable(pte, XENFEAT_writable_page_tables);
 }
 
 extern void pte_free(struct page *pte);
 
-#define __pte_free_tlb(tlb,pte) tlb_remove_page((tlb),(pte))
+#define __pte_free_tlb(tlb,pte) pte_free(pte)
 
 #ifdef CONFIG_X86_PAE
 /*


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