[PATCH v5 01/11] thp: huge zero page: basic preparation

Kirill A. Shutemov
2012-11-07T15:00:13Z

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

Huge zero page (hzp) is a non-movable huge page (2M on x86-64) filled
with zeros.

For now let's allocate the page on hugepage_init(). We'll switch to lazy
allocation later.

We are not going to map the huge zero page until we can handle it
properly on all code paths.

is_huge_zero_{pfn,pmd}() functions will be used by following patches to
check whether the pfn/pmd is huge zero page.

Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
---
mm/huge_memory.c | 30 ++++++++++++++++++++++++++++++
1 files changed, 30 insertions(+), 0 deletions(-)

diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index 40f17c3..e5ce979 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -47,6 +47,7 @@ static unsigned int khugepaged_scan_sleep_millisecs __read_mostly = 10000;
/* during fragmentation poll the hugepage allocator once every minute */
static unsigned int khugepaged_alloc_sleep_millisecs __read_mostly = 60000;
static struct task_struct *khugepaged_thread __read_mostly;
+static unsigned long huge_zero_pfn __read_mostly;
static DEFINE_MUTEX(khugepaged_mutex);
static DEFINE_SPINLOCK(khugepaged_mm_lock);
static DECLARE_WAIT_QUEUE_HEAD(khugepaged_wait);
@@ -159,6 +160,29 @@ static int start_khugepaged(void)
return err;
}

+static int init_huge_zero_page(void)
+{
+ struct page *hpage;
+
+ hpage = alloc_pages((GFP_TRANSHUGE | __GFP_ZERO) & ~__GFP_MOVABLE,
+ HPAGE_PMD_ORDER);
+ if (!hpage)
+ return -ENOMEM;
+
+ huge_zero_pfn = page_to_pfn(hpage);
+ return 0;
+}
+
+static inline bool is_huge_zero_pfn(unsigned long pfn)
+{
+ return pfn == huge_zero_pfn;
+}
+
+static inline bool is_huge_zero_pmd(pmd_t pmd)
+{
+ return is_huge_zero_pfn(pmd_pfn(pmd));
+}
+
#ifdef CONFIG_SYSFS

static ssize_t double_flag_show(struct kobject *kobj,
@@ -540,6 +564,10 @@ 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;
@@ -562,6 +590,8 @@ 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;
}
--
1.7.7.6