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>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 19 insertions, 2 deletions

diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index 9a5d45dfad44..72835cea0b0f 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -39,7 +39,8 @@ 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;
@@ -357,6 +358,20 @@ 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)
@@ -378,6 +393,7 @@ 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
@@ -779,7 +795,8 @@ 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);