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thp: introduce sysfs knob to disable huge zero page

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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>
This commit is contained in:
Kirill A. Shutemov 2012-12-12 13:51:12 -08:00 committed by Linus Torvalds
parent d8a8e1f0da
commit 79da5407ee
3 changed files with 30 additions and 2 deletions
Show stats Download patch file Download diff file Expand all files Collapse all files

7
Documentation/vm/transhuge.txt
View file

@ -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".

4
include/linux/huge_mm.h
View file

@ -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 & \

21
mm/huge_memory.c
View file

@ -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);