linux x86/64: No need to pre-allocate all fixmap pagetables:

just those for bt_ioremap().
Signed-off-by: Keir Fraser <keir@xensource.com>

diff --git a/linux-2.6-xen-sparse/arch/x86_64/mm/init-xen.c b/linux-2.6-xen-sparse/arch/x86_64/mm/init-xen.c
index dbaec6e1c93ef4d1abbec2846371bc44cf086a58..de7c80dfb843e6120cb0c95b94c87ab2701e6ea9 100644 (file)
--- a/linux-2.6-xen-sparse/arch/x86_64/mm/init-xen.c
+++ b/linux-2.6-xen-sparse/arch/x86_64/mm/init-xen.c
@@ -708,19 +708,22 @@ static void xen_finish_init_mapping(void)
                WARN_ON(HYPERVISOR_update_va_mapping(
                        start, __pte_ma(0), 0));
 
-       /* Initialise all fixmap pagetables. Use 'start_pfn' allocator. */
+       /* Allocate pte's for initial fixmaps from 'start_pfn' allocator. */
        table_end = ~0UL;
-       for (i = 0; i < __end_of_fixed_addresses; i++)
+
+       /*
+        * Prefetch pte's for the bt_ioremap() area. It gets used before the
+        * boot-time allocator is online, so allocate-on-demand would fail.
+        */
+       for (i = FIX_BTMAP_END; i <= FIX_BTMAP_BEGIN; i++)
                __set_fixmap(i, 0, __pgprot(0));
-       table_end = start_pfn;
 
-       /* Switch to the real shared_info page, and clear the
-        * dummy page. */
+       /* Switch to the real shared_info page, and clear the dummy page. */
        set_fixmap(FIX_SHARED_INFO, xen_start_info->shared_info);
        HYPERVISOR_shared_info = (shared_info_t *)fix_to_virt(FIX_SHARED_INFO);
        memset(empty_zero_page, 0, sizeof(empty_zero_page));
 
-       /* Setup mapping of lower 1st MB */
+       /* Set up mapping of lowest 1MB of physical memory. */
        for (i = 0; i < NR_FIX_ISAMAPS; i++)
                if (is_initial_xendomain())
                        set_fixmap(FIX_ISAMAP_BEGIN - i, i * PAGE_SIZE);
@@ -729,6 +732,9 @@ static void xen_finish_init_mapping(void)
                                     virt_to_mfn(empty_zero_page)
                                     << PAGE_SHIFT,
                                     PAGE_KERNEL_RO);
+
+       /* Disable the 'start_pfn' allocator. */
+       table_end = start_pfn;
 }
 
 /* Setup the direct mapping of the physical memory at PAGE_OFFSET.