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[Xen-devel] [PATCH 3/7] x86: map frame table sparsely

To: <xen-devel@xxxxxxxxxxxxxxxxxxx>
Subject: [Xen-devel] [PATCH 3/7] x86: map frame table sparsely
From: "Jan Beulich" <JBeulich@xxxxxxxxxx>
Date: Mon, 21 Sep 2009 13:06:38 +0100
Delivery-date: Mon, 21 Sep 2009 05:08:53 -0700
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Avoid backing frame table holes with memory, when those holes are large
enough to cover an exact multiple of large pages. This is based on the
introduction of a bit map, where each bit represents one such range,
thus allowing mfn_valid() checks to easily filter out those MFNs that
now shouldn't be used to index the frame table.

This allows for saving a couple of 2M pages even on "normal" systems.

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

--- 2009-09-21.orig/xen/arch/x86/mm.c   2009-09-21 11:13:02.000000000 +0200
+++ 2009-09-21/xen/arch/x86/mm.c        2009-09-21 11:14:51.000000000 +0200
@@ -141,6 +141,10 @@ struct domain *dom_xen, *dom_io;
 unsigned long max_page;
 unsigned long total_pages;
 
+unsigned long __read_mostly pdx_group_valid[BITS_TO_LONGS(
+    (FRAMETABLE_SIZE / sizeof(*frame_table) + PDX_GROUP_COUNT - 1)
+    / PDX_GROUP_COUNT)] = { [0] = 1 };
+
 #define PAGE_CACHE_ATTRS (_PAGE_PAT|_PAGE_PCD|_PAGE_PWT)
 
 int opt_allow_hugepage;
@@ -162,36 +166,58 @@ l2_pgentry_t *compat_idle_pg_table_l2 = 
 #define l3_disallow_mask(d) L3_DISALLOW_MASK
 #endif
 
+static void __init init_frametable_chunk(void *start, void *end)
+{
+    unsigned long s = (unsigned long)start;
+    unsigned long e = (unsigned long)end;
+    unsigned long step, mfn;
+
+    ASSERT(!(s & ((1 << L2_PAGETABLE_SHIFT) - 1)));
+    for ( ; s < e; s += step << PAGE_SHIFT )
+    {
+        step = 1UL << (cpu_has_page1gb &&
+                       !(s & ((1UL << L3_PAGETABLE_SHIFT) - 1)) ?
+                       L3_PAGETABLE_SHIFT - PAGE_SHIFT :
+                       L2_PAGETABLE_SHIFT - PAGE_SHIFT);
+        /*
+         * The hardcoded 4 below is arbitrary - just pick whatever you think
+         * is reasonable to waste as a trade-off for using a large page.
+         */
+        while ( step && s + (step << PAGE_SHIFT) > e + (4 << PAGE_SHIFT) )
+            step >>= PAGETABLE_ORDER;
+        do {
+            mfn = alloc_boot_pages(step, step);
+        } while ( !mfn && (step >>= PAGETABLE_ORDER) );
+        if ( !mfn )
+            panic("Not enough memory for frame table");
+        map_pages_to_xen(s, mfn, step, PAGE_HYPERVISOR);
+    }
+
+    memset(start, 0, end - start);
+    memset(end, -1, s - (unsigned long)end);
+}
+
 void __init init_frametable(void)
 {
-    unsigned long nr_pages, page_step, i, mfn;
+    unsigned int sidx, eidx, nidx;
+    unsigned int max_idx = (max_pdx + PDX_GROUP_COUNT - 1) / PDX_GROUP_COUNT;
 
 #ifdef __x86_64__
-    BUILD_BUG_ON(FRAMETABLE_VIRT_START & ((1UL << L3_PAGETABLE_SHIFT) - 1));
     BUILD_BUG_ON(XEN_VIRT_END > FRAMETABLE_VIRT_END);
-#else
-    BUILD_BUG_ON(FRAMETABLE_VIRT_START & ((1UL << L2_PAGETABLE_SHIFT) - 1));
 #endif
+    BUILD_BUG_ON(FRAMETABLE_VIRT_START & ((1UL << L2_PAGETABLE_SHIFT) - 1));
 
-    nr_pages  = PFN_UP(max_pdx * sizeof(*frame_table));
-    page_step = 1 << (cpu_has_page1gb ? L3_PAGETABLE_SHIFT - PAGE_SHIFT
-                                      : L2_PAGETABLE_SHIFT - PAGE_SHIFT);
-
-    for ( i = 0; i < nr_pages; i += page_step )
+    for ( sidx = 0; ; sidx = nidx )
     {
-        /*
-         * The hardcoded 4 below is arbitrary - just pick whatever you think
-         * is reasonable to waste as a trade-off for using a large page.
-         */
-        while (nr_pages + 4 - i < page_step)
-            page_step >>= PAGETABLE_ORDER;
-        mfn = alloc_boot_pages(page_step, page_step);
-        map_pages_to_xen(
-            FRAMETABLE_VIRT_START + (i << PAGE_SHIFT),
-            mfn, page_step, PAGE_HYPERVISOR);
+        eidx = find_next_zero_bit(pdx_group_valid, max_idx, sidx);
+        nidx = find_next_bit(pdx_group_valid, max_idx, eidx);
+        if ( nidx >= max_idx )
+            break;
+        init_frametable_chunk(pdx_to_page(sidx * PDX_GROUP_COUNT),
+                              pdx_to_page(eidx * PDX_GROUP_COUNT));
     }
-
-    memset(frame_table, 0, nr_pages << PAGE_SHIFT);
+    init_frametable_chunk(pdx_to_page(sidx * PDX_GROUP_COUNT),
+                          pdx_to_page(max_pdx - 1) + 1);
 }
 
 void __init arch_init_memory(void)
--- 2009-09-21.orig/xen/arch/x86/setup.c        2009-09-21 11:13:02.000000000 
+0200
+++ 2009-09-21/xen/arch/x86/setup.c     2009-09-21 11:14:51.000000000 +0200
@@ -312,6 +312,16 @@ static void __init setup_max_pdx(void)
 #endif
 }
 
+static void __init set_pdx_range(unsigned long smfn, unsigned long emfn)
+{
+    unsigned long idx, eidx;
+
+    idx = pfn_to_pdx(smfn) / PDX_GROUP_COUNT;
+    eidx = (pfn_to_pdx(emfn - 1) + PDX_GROUP_COUNT) / PDX_GROUP_COUNT;
+    for ( ; idx < eidx; ++idx )
+        __set_bit(idx, pdx_group_valid);
+}
+
 /* A temporary copy of the e820 map that we can mess with during bootstrap. */
 static struct e820map __initdata boot_e820;
 
@@ -657,6 +667,8 @@ void __init __start_xen(unsigned long mb
         if ( (boot_e820.map[i].type != E820_RAM) || (s >= e) )
             continue;
 
+        set_pdx_range(s >> PAGE_SHIFT, e >> PAGE_SHIFT);
+
         /* Map the chunk. No memory will need to be allocated to do this. */
         map_pages_to_xen(
             (unsigned long)maddr_to_bootstrap_virt(s),
@@ -853,6 +865,8 @@ void __init __start_xen(unsigned long mb
         }
 #endif
 
+        set_pdx_range(s >> PAGE_SHIFT, e >> PAGE_SHIFT);
+
         /* Need to create mappings above 16MB. */
         map_s = max_t(uint64_t, s, 16<<20);
         map_e = e;
--- 2009-09-21.orig/xen/arch/x86/x86_64/mm.c    2009-09-21 11:13:02.000000000 
+0200
+++ 2009-09-21/xen/arch/x86/x86_64/mm.c 2009-09-21 11:14:51.000000000 +0200
@@ -64,6 +64,14 @@ l3_pgentry_t __attribute__ ((__section__
 l2_pgentry_t __attribute__ ((__section__ (".bss.page_aligned")))
     l2_xenmap[L2_PAGETABLE_ENTRIES];
 
+int __mfn_valid(unsigned long mfn)
+{
+    return likely(mfn < max_page) &&
+           likely(!(mfn & pfn_hole_mask)) &&
+           likely(test_bit(pfn_to_pdx(mfn) / PDX_GROUP_COUNT,
+                           pdx_group_valid));
+}
+
 void *alloc_xen_pagetable(void)
 {
     extern int early_boot;
--- 2009-09-21.orig/xen/include/asm-x86/config.h        2009-09-21 
11:13:02.000000000 +0200
+++ 2009-09-21/xen/include/asm-x86/config.h     2009-09-21 11:14:51.000000000 
+0200
@@ -314,7 +314,8 @@ extern unsigned int video_mode, video_fl
 #define RDWR_MPT_VIRT_END      LINEAR_PT_VIRT_START
 #define RDWR_MPT_VIRT_START    (RDWR_MPT_VIRT_END - (MACHPHYS_MBYTES<<20))
 #define FRAMETABLE_VIRT_END    RDWR_MPT_VIRT_START
-#define FRAMETABLE_VIRT_START  (FRAMETABLE_VIRT_END - (FRAMETABLE_MBYTES<<20))
+#define FRAMETABLE_SIZE         (FRAMETABLE_MBYTES<<20)
+#define FRAMETABLE_VIRT_START  (FRAMETABLE_VIRT_END - FRAMETABLE_SIZE)
 #define RO_MPT_VIRT_END                FRAMETABLE_VIRT_START
 #define RO_MPT_VIRT_START      (RO_MPT_VIRT_END - (MACHPHYS_MBYTES<<20))
 
--- 2009-09-21.orig/xen/include/asm-x86/mm.h    2009-09-21 11:13:02.000000000 
+0200
+++ 2009-09-21/xen/include/asm-x86/mm.h 2009-09-21 11:14:51.000000000 +0200
@@ -263,6 +263,10 @@ extern unsigned long max_page;
 extern unsigned long total_pages;
 void init_frametable(void);
 
+#define PDX_GROUP_COUNT ((1 << L2_PAGETABLE_SHIFT) / \
+                         (sizeof(*frame_table) & -sizeof(*frame_table)))
+extern unsigned long pdx_group_valid[];
+
 /* Convert between Xen-heap virtual addresses and page-info structures. */
 static inline struct page_info *__virt_to_page(const void *v)
 {
--- 2009-09-21.orig/xen/include/asm-x86/x86_32/page.h   2009-09-21 
11:13:02.000000000 +0200
+++ 2009-09-21/xen/include/asm-x86/x86_32/page.h        2009-09-21 
11:14:51.000000000 +0200
@@ -41,7 +41,11 @@
 #include <xen/config.h>
 #include <asm/types.h>
 
-#define __mfn_valid(mfn)        ((mfn) < max_page)
+#define __mfn_valid(mfn)        ({                                            \
+    unsigned long __m_f_n = (mfn);                                            \
+    likely(__m_f_n < max_page) &&                                             \
+    likely(test_bit(pfn_to_pdx(__m_f_n) / PDX_GROUP_COUNT, pdx_group_valid)); \
+})
 
 #define max_pdx                 max_page
 #define pfn_to_pdx(pfn)         (pfn)
--- 2009-09-21.orig/xen/include/asm-x86/x86_64/page.h   2009-09-21 
11:13:02.000000000 +0200
+++ 2009-09-21/xen/include/asm-x86/x86_64/page.h        2009-09-21 
11:14:51.000000000 +0200
@@ -35,7 +35,7 @@
 /* Physical address where Xen was relocated to. */
 extern unsigned long xen_phys_start;
 
-extern unsigned long max_page, max_pdx;
+extern unsigned long max_pdx;
 extern unsigned long pfn_pdx_bottom_mask, ma_va_bottom_mask;
 extern unsigned int pfn_pdx_hole_shift;
 extern unsigned long pfn_hole_mask;
@@ -53,10 +53,7 @@ extern void pfn_pdx_hole_setup(unsigned 
 #define pdx_to_virt(pdx) ((void *)(DIRECTMAP_VIRT_START + \
                                    ((unsigned long)(pdx) << PAGE_SHIFT)))
 
-static inline int __mfn_valid(unsigned long mfn)
-{
-    return mfn < max_page && !(mfn & pfn_hole_mask);
-}
+extern int __mfn_valid(unsigned long mfn);
 
 static inline unsigned long pfn_to_pdx(unsigned long pfn)
 {



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