[PATCH v5 09/11] thp: lazy huge zero page allocation

Kirill A. Shutemov
2012-11-07T15:00:39Z

From: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>

Instead of allocating huge zero page on hugepage_init() we can postpone it
until first huge zero page map. It saves memory if THP is not in use.

cmpxchg() is used to avoid race on huge_zero_pfn initialization.

Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
---
mm/huge_memory.c | 20 ++++++++++----------
1 files changed, 10 insertions(+), 10 deletions(-)

diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index 41f05f1..52073c2 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -160,22 +160,24 @@ static int start_khugepaged(void)
return err;
}

-static int init_huge_zero_page(void)
+static int init_huge_zero_pfn(void)
{
struct page *hpage;
+ unsigned long pfn;

hpage = alloc_pages((GFP_TRANSHUGE | __GFP_ZERO) & ~__GFP_MOVABLE,
HPAGE_PMD_ORDER);
if (!hpage)
return -ENOMEM;
-
- huge_zero_pfn = page_to_pfn(hpage);
+ pfn = page_to_pfn(hpage);
+ if (cmpxchg(&huge_zero_pfn, 0, pfn))
+ __free_page(hpage);
return 0;
}

static inline bool is_huge_zero_pfn(unsigned long pfn)
{
- return pfn == huge_zero_pfn;
+ return huge_zero_pfn && pfn == huge_zero_pfn;
}

static inline bool is_huge_zero_pmd(pmd_t pmd)
@@ -564,10 +566,6 @@ static int __init hugepage_init(void)
if (err)
return err;

- err = init_huge_zero_page();
- if (err)
- goto out;
-
err = khugepaged_slab_init();
if (err)
goto out;
@@ -590,8 +588,6 @@ static int __init hugepage_init(void)

return 0;
out:
- if (huge_zero_pfn)
- __free_page(pfn_to_page(huge_zero_pfn));
hugepage_exit_sysfs(hugepage_kobj);
return err;
}
@@ -728,6 +724,10 @@ int do_huge_pmd_anonymous_page(struct mm_struct *mm, struct vm_area_struct *vma,
return VM_FAULT_OOM;
if (!(flags & FAULT_FLAG_WRITE)) {
pgtable_t pgtable;
+ if (unlikely(!huge_zero_pfn && init_huge_zero_pfn())) {
+ count_vm_event(THP_FAULT_FALLBACK);
+ goto out;
+ }
pgtable = pte_alloc_one(mm, haddr);
if (unlikely(!pgtable))
goto out;
--
1.7.7.6