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Message-Id: <20080103172705.2D78414DDD@wotan.suse.de>
Date: Thu, 3 Jan 2008 18:27:05 +0100 (CET)
From: Andi Kleen <ak@...e.de>
To: linux-kernel@...r.kernel.org
Subject: [PATCH] [8/8] GBPAGES: Do kernel direct mapping at boot using GB pages
This should decrease TLB pressure because the kernel will need
less TLB faults for its own data access.
Only done for 64bit because i386 does not support GB page tables.
This only applies to the data portion of the direct mapping; the
kernel text mapping stays with 2MB pages because the AMD Fam10h
microarchitecture does not support GB ITLBs and AMD recommends
against using GB mappings for code.
Can be disabled with direct_gbpages=off
Signed-off-by: Andi Kleen <ak@...e.de>
---
arch/x86/mm/init_64.c | 63 ++++++++++++++++++++++++++++++++++++++++++--------
1 file changed, 54 insertions(+), 9 deletions(-)
Index: linux/arch/x86/mm/init_64.c
===================================================================
--- linux.orig/arch/x86/mm/init_64.c
+++ linux/arch/x86/mm/init_64.c
@@ -264,13 +264,20 @@ __meminit void early_iounmap(void *addr,
__flush_tlb();
}
+static unsigned long direct_entry(unsigned long paddr)
+{
+ unsigned long entry;
+ entry = __PAGE_KERNEL_LARGE|_PAGE_GLOBAL|paddr;
+ entry &= __supported_pte_mask;
+ return entry;
+}
+
static void __meminit
phys_pmd_init(pmd_t *pmd_page, unsigned long address, unsigned long end)
{
int i = pmd_index(address);
for (; i < PTRS_PER_PMD; i++, address += PMD_SIZE) {
- unsigned long entry;
pmd_t *pmd = pmd_page + pmd_index(address);
if (address >= end) {
@@ -283,9 +290,7 @@ phys_pmd_init(pmd_t *pmd_page, unsigned
if (pmd_val(*pmd))
continue;
- entry = __PAGE_KERNEL_LARGE|_PAGE_GLOBAL|address;
- entry &= __supported_pte_mask;
- set_pmd(pmd, __pmd(entry));
+ set_pmd(pmd, __pmd(direct_entry(address)));
}
}
@@ -318,7 +323,13 @@ static void __meminit phys_pud_init(pud_
}
if (pud_val(*pud)) {
- phys_pmd_update(pud, addr, end);
+ if (!pud_large(*pud))
+ phys_pmd_update(pud, addr, end);
+ continue;
+ }
+
+ if (direct_gbpages > 0) {
+ set_pud(pud, __pud(direct_entry(addr)));
continue;
}
@@ -337,9 +348,11 @@ static void __init find_early_table_spac
unsigned long puds, pmds, tables, start;
puds = (end + PUD_SIZE - 1) >> PUD_SHIFT;
- pmds = (end + PMD_SIZE - 1) >> PMD_SHIFT;
- tables = round_up(puds * sizeof(pud_t), PAGE_SIZE) +
- round_up(pmds * sizeof(pmd_t), PAGE_SIZE);
+ tables = round_up(puds * sizeof(pud_t), PAGE_SIZE);
+ if (!direct_gbpages) {
+ pmds = (end + PMD_SIZE - 1) >> PMD_SHIFT;
+ tables += round_up(pmds * sizeof(pmd_t), PAGE_SIZE);
+ }
/* RED-PEN putting page tables only on node 0 could
cause a hotspot and fill up ZONE_DMA. The page tables
@@ -372,8 +385,15 @@ void __init_refok init_memory_mapping(un
* mapped. Unfortunately this is done currently before the nodes are
* discovered.
*/
- if (!after_bootmem)
+ if (!after_bootmem) {
+ if (direct_gbpages >= 0 && cpu_has_gbpages) {
+ printk(KERN_INFO "Using GB pages for direct mapping\n");
+ direct_gbpages = 1;
+ } else
+ direct_gbpages = 0;
+
find_early_table_space(end);
+ }
start = (unsigned long)__va(start);
end = (unsigned long)__va(end);
@@ -419,6 +439,27 @@ void __init paging_init(void)
}
#endif
+static void split_gb_page(pud_t *pud, unsigned long paddr)
+{
+ int i;
+ pmd_t *pmd;
+ struct page *p = alloc_page(GFP_KERNEL);
+ if (!p)
+ return;
+
+ Dprintk("split_gb_page %lx\n", paddr);
+
+ SetPagePrivate(p);
+ /* Set reference to 1 so that c_p_a() does not undo it */
+ page_private(p) = 1;
+
+ paddr &= PUD_PAGE_MASK;
+ pmd = page_address(p);
+ for (i = 0; i < PTRS_PER_PTE; i++, paddr += PMD_PAGE_SIZE)
+ pmd[i] = __pmd(direct_entry(paddr));
+ pud_populate(NULL, pud, pmd);
+}
+
/* Unmap a kernel mapping if it exists. This is useful to avoid prefetches
from the CPU leading to inconsistent cache lines. address and size
must be aligned to 2MB boundaries.
@@ -430,6 +471,8 @@ __clear_kernel_mapping(unsigned long add
BUG_ON(address & ~PMD_PAGE_MASK);
BUG_ON(size & ~PMD_PAGE_MASK);
+
+ Dprintk("clear_kernel_mapping %lx-%lx\n", address, address+size);
for (; address < end; address += PMD_PAGE_SIZE) {
pgd_t *pgd = pgd_offset_k(address);
@@ -438,6 +481,8 @@ __clear_kernel_mapping(unsigned long add
if (pgd_none(*pgd))
continue;
pud = pud_offset(pgd, address);
+ if (pud_large(*pud))
+ split_gb_page(pud, __pa(address));
if (pud_none(*pud))
continue;
pmd = pmd_offset(pud, address);
--
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