thp: introduce sysfs knob to disable huge zero page

By default kernel tries to use huge zero page on read page fault.  It's
possible to disable huge zero page by writing 0 or enable it back by
writing 1:

echo 0 >/sys/kernel/mm/transparent_hugepage/khugepaged/use_zero_page
echo 1 >/sys/kernel/mm/transparent_hugepage/khugepaged/use_zero_page

Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Andi Kleen <ak@linux.intel.com>
Cc: "H. Peter Anvin" <hpa@linux.intel.com>
Cc: Mel Gorman <mel@csn.ul.ie>
Cc: David Rientjes <rientjes@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/Documentation/vm/transhuge.txt b/Documentation/vm/transhuge.txt
index 60aeedd54615328c00937691685066f9348c0fe5..8785fb87d9c79fe37f385bf3beb48e7ca72f4a41 100644 (file)
--- a/Documentation/vm/transhuge.txt
+++ b/Documentation/vm/transhuge.txt
@@ -116,6 +116,13 @@ echo always >/sys/kernel/mm/transparent_hugepage/defrag
 echo madvise >/sys/kernel/mm/transparent_hugepage/defrag
 echo never >/sys/kernel/mm/transparent_hugepage/defrag
 
+By default kernel tries to use huge zero page on read page fault.
+It's possible to disable huge zero page by writing 0 or enable it
+back by writing 1:
+
+echo 0 >/sys/kernel/mm/transparent_hugepage/khugepaged/use_zero_page
+echo 1 >/sys/kernel/mm/transparent_hugepage/khugepaged/use_zero_page
+
 khugepaged will be automatically started when
 transparent_hugepage/enabled is set to "always" or "madvise, and it'll
 be automatically shutdown if it's set to "never".

diff --git a/include/linux/huge_mm.h b/include/linux/huge_mm.h
index 5d50f6583085748a00d6a206eb55074a045cf4a4..b874015cbc78456b523f33e3ac9f15a22c05d09c 100644 (file)
--- a/include/linux/huge_mm.h
+++ b/include/linux/huge_mm.h
@@ -39,6 +39,7 @@ enum transparent_hugepage_flag {
        TRANSPARENT_HUGEPAGE_DEFRAG_FLAG,
        TRANSPARENT_HUGEPAGE_DEFRAG_REQ_MADV_FLAG,
        TRANSPARENT_HUGEPAGE_DEFRAG_KHUGEPAGED_FLAG,
+       TRANSPARENT_HUGEPAGE_USE_ZERO_PAGE_FLAG,
 #ifdef CONFIG_DEBUG_VM
        TRANSPARENT_HUGEPAGE_DEBUG_COW_FLAG,
 #endif
@@ -78,6 +79,9 @@ extern bool is_vma_temporary_stack(struct vm_area_struct *vma);
         (transparent_hugepage_flags &                                  \
          (1<<TRANSPARENT_HUGEPAGE_DEFRAG_REQ_MADV_FLAG) &&             \
          (__vma)->vm_flags & VM_HUGEPAGE))
+#define transparent_hugepage_use_zero_page()                           \
+       (transparent_hugepage_flags &                                   \
+        (1<<TRANSPARENT_HUGEPAGE_USE_ZERO_PAGE_FLAG))
 #ifdef CONFIG_DEBUG_VM
 #define transparent_hugepage_debug_cow()                               \
        (transparent_hugepage_flags &                                   \

diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index 95747f6445d353c1d51f98c53153cccb696b9e52..e0de3c9ca1dc07aea81ab588b5e8e888eb2d5c91 100644 (file)
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -40,7 +40,8 @@ unsigned long transparent_hugepage_flags __read_mostly =
        (1<<TRANSPARENT_HUGEPAGE_REQ_MADV_FLAG)|
 #endif
        (1<<TRANSPARENT_HUGEPAGE_DEFRAG_FLAG)|
-       (1<<TRANSPARENT_HUGEPAGE_DEFRAG_KHUGEPAGED_FLAG);
+       (1<<TRANSPARENT_HUGEPAGE_DEFRAG_KHUGEPAGED_FLAG)|
+       (1<<TRANSPARENT_HUGEPAGE_USE_ZERO_PAGE_FLAG);
 
 /* default scan 8*512 pte (or vmas) every 30 second */
 static unsigned int khugepaged_pages_to_scan __read_mostly = HPAGE_PMD_NR*8;
@@ -358,6 +359,20 @@ static ssize_t defrag_store(struct kobject *kobj,
 static struct kobj_attribute defrag_attr =
        __ATTR(defrag, 0644, defrag_show, defrag_store);
 
+static ssize_t use_zero_page_show(struct kobject *kobj,
+               struct kobj_attribute *attr, char *buf)
+{
+       return single_flag_show(kobj, attr, buf,
+                               TRANSPARENT_HUGEPAGE_USE_ZERO_PAGE_FLAG);
+}
+static ssize_t use_zero_page_store(struct kobject *kobj,
+               struct kobj_attribute *attr, const char *buf, size_t count)
+{
+       return single_flag_store(kobj, attr, buf, count,
+                                TRANSPARENT_HUGEPAGE_USE_ZERO_PAGE_FLAG);
+}
+static struct kobj_attribute use_zero_page_attr =
+       __ATTR(use_zero_page, 0644, use_zero_page_show, use_zero_page_store);
 #ifdef CONFIG_DEBUG_VM
 static ssize_t debug_cow_show(struct kobject *kobj,
                                struct kobj_attribute *attr, char *buf)
@@ -379,6 +394,7 @@ static struct kobj_attribute debug_cow_attr =
 static struct attribute *hugepage_attr[] = {
        &enabled_attr.attr,
        &defrag_attr.attr,
+       &use_zero_page_attr.attr,
 #ifdef CONFIG_DEBUG_VM
        &debug_cow_attr.attr,
 #endif
@@ -780,7 +796,8 @@ int do_huge_pmd_anonymous_page(struct mm_struct *mm, struct vm_area_struct *vma,
                        return VM_FAULT_OOM;
                if (unlikely(khugepaged_enter(vma)))
                        return VM_FAULT_OOM;
-               if (!(flags & FAULT_FLAG_WRITE)) {
+               if (!(flags & FAULT_FLAG_WRITE) &&
+                               transparent_hugepage_use_zero_page()) {
                        pgtable_t pgtable;
                        unsigned long zero_pfn;
                        pgtable = pte_alloc_one(mm, haddr);