[Xen-devel] [PATCH 1/3] x86: calculate precisely the memory needed by init_memory_mapping

[<stefano.stabellini@xxxxxxxxxxxxx>]

From: Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>

- take into account the size of the initial pagetable;

- remove the extra PMD_SIZE added when use_pse, because the previously
allocated PMDs are always 2M aligned;

- remove the extra page added on x86_32 for the fixmap because is not
needed: the PMD entry is already allocated and contiguous for the whole
range (a PMD page covers 4G of virtual addresses) and the pte entry is
already allocated by early_ioremap_init.

Signed-off-by: Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>
Reviewed-by: Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>
---
 arch/x86/mm/init.c |   62 ++++++++++++++++++++++++++++++++++++++-------------
 1 files changed, 46 insertions(+), 16 deletions(-)

diff --git a/arch/x86/mm/init.c b/arch/x86/mm/init.c
index 3032644..0cfe8d4 100644
--- a/arch/x86/mm/init.c
+++ b/arch/x86/mm/init.c
@@ -28,22 +28,52 @@ int direct_gbpages
 #endif
 ;
 
-static void __init find_early_table_space(unsigned long end, int use_pse,
-                                         int use_gbpages)
+static void __init find_early_table_space(unsigned long start,
+               unsigned long end, int use_pse, int use_gbpages)
 {
-       unsigned long puds, pmds, ptes, tables, start = 0, good_end = end;
+       unsigned long pmds = 0, ptes = 0, tables = 0, good_end = end,
+                                 pud_mapped = 0, pmd_mapped = 0, size = end - 
start;
        phys_addr_t base;
 
-       puds = (end + PUD_SIZE - 1) >> PUD_SHIFT;
-       tables = roundup(puds * sizeof(pud_t), PAGE_SIZE);
+       pud_mapped = DIV_ROUND_UP(PFN_PHYS(max_pfn_mapped),
+                       (PUD_SIZE * PTRS_PER_PUD));
+       pud_mapped *= (PUD_SIZE * PTRS_PER_PUD);
+       pmd_mapped = DIV_ROUND_UP(PFN_PHYS(max_pfn_mapped),
+                       (PMD_SIZE * PTRS_PER_PMD));
+       pmd_mapped *= (PMD_SIZE * PTRS_PER_PMD);
+
+       if (start < PFN_PHYS(max_pfn_mapped)) {
+               if (PFN_PHYS(max_pfn_mapped) < end)
+                       size -= PFN_PHYS(max_pfn_mapped) - start;
+               else
+                       size = 0;
+       }
+
+#ifndef __PAGETABLE_PUD_FOLDED
+       if (end > pud_mapped) {
+               unsigned long puds;
+               if (start < pud_mapped)
+                       puds = (end - pud_mapped + PUD_SIZE - 1) >> PUD_SHIFT;
+               else
+                       puds = (end - start + PUD_SIZE - 1) >> PUD_SHIFT;
+               tables += roundup(puds * sizeof(pud_t), PAGE_SIZE);
+       }
+#endif
 
        if (use_gbpages) {
                unsigned long extra;
 
                extra = end - ((end>>PUD_SHIFT) << PUD_SHIFT);
                pmds = (extra + PMD_SIZE - 1) >> PMD_SHIFT;
-       } else
-               pmds = (end + PMD_SIZE - 1) >> PMD_SHIFT;
+       }
+#ifndef __PAGETABLE_PMD_FOLDED
+       else if (end > pmd_mapped) {
+               if (start < pmd_mapped)
+                       pmds = (end - pmd_mapped + PMD_SIZE - 1) >> PMD_SHIFT;
+               else
+                       pmds = (end - start + PMD_SIZE - 1) >> PMD_SHIFT;
+       }
+#endif
 
        tables += roundup(pmds * sizeof(pmd_t), PAGE_SIZE);
 
@@ -51,23 +81,20 @@ static void __init find_early_table_space(unsigned long 
end, int use_pse,
                unsigned long extra;
 
                extra = end - ((end>>PMD_SHIFT) << PMD_SHIFT);
-#ifdef CONFIG_X86_32
-               extra += PMD_SIZE;
-#endif
                ptes = (extra + PAGE_SIZE - 1) >> PAGE_SHIFT;
        } else
-               ptes = (end + PAGE_SIZE - 1) >> PAGE_SHIFT;
+               ptes = (size + PAGE_SIZE - 1) >> PAGE_SHIFT;
 
        tables += roundup(ptes * sizeof(pte_t), PAGE_SIZE);
 
-#ifdef CONFIG_X86_32
-       /* for fixmap */
-       tables += roundup(__end_of_fixed_addresses * sizeof(pte_t), PAGE_SIZE);
+       if (!tables)
+               return;
 
+#ifdef CONFIG_X86_32
        good_end = max_pfn_mapped << PAGE_SHIFT;
 #endif
 
-       base = memblock_find_in_range(start, good_end, tables, PAGE_SIZE);
+       base = memblock_find_in_range(0x00, good_end, tables, PAGE_SIZE);
        if (base == MEMBLOCK_ERROR)
                panic("Cannot find space for the kernel page tables");
 
@@ -261,7 +288,7 @@ unsigned long __init_refok init_memory_mapping(unsigned 
long start,
         * nodes are discovered.
         */
        if (!after_bootmem)
-               find_early_table_space(end, use_pse, use_gbpages);
+               find_early_table_space(start, end, use_pse, use_gbpages);
 
        for (i = 0; i < nr_range; i++)
                ret = kernel_physical_mapping_init(mr[i].start, mr[i].end,
@@ -275,6 +302,9 @@ unsigned long __init_refok init_memory_mapping(unsigned 
long start,
 
        __flush_tlb_all();
 
+       if (pgt_buf_end != pgt_buf_top)
+               printk(KERN_DEBUG "initial kernel pagetable allocation wasted 
%lx"
+                               " pages\n", pgt_buf_top - pgt_buf_end);
        /*
         * Reserve the kernel pagetable pages we used (pgt_buf_start -
         * pgt_buf_end) and free the other ones (pgt_buf_end - pgt_buf_top)
-- 
1.7.2.3


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