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Date: Fri, 15 Nov 2013 14:55:53 -0800
From: Dave Hansen <dave@...1.net>
To: linux-mm@...ck.org
Cc: linux-kernel@...r.kernel.org, dave.jiang@...el.com,
akpm@...ux-foundation.org, dhillf@...il.com,
Naoya Horiguchi <n-horiguchi@...jp.nec.com>,
Mel Gorman <mgorman@...e.de>, Dave Hansen <dave@...1.net>
Subject: [v3][PATCH 2/2] mm: thp: give transparent hugepage code a separate copy_page
Changes from v2:
*
Changes from v1:
* removed explicit might_sleep() in favor of the one that we
get from the cond_resched();
--
From: Dave Hansen <dave.hansen@...ux.intel.com>
Right now, the migration code in migrate_page_copy() uses
copy_huge_page() for hugetlbfs and thp pages:
if (PageHuge(page) || PageTransHuge(page))
copy_huge_page(newpage, page);
So, yay for code reuse. But:
void copy_huge_page(struct page *dst, struct page *src)
{
struct hstate *h = page_hstate(src);
and a non-hugetlbfs page has no page_hstate(). This works 99% of
the time because page_hstate() determines the hstate from the
page order alone. Since the page order of a THP page matches the
default hugetlbfs page order, it works.
But, if you change the default huge page size on the boot
command-line (say default_hugepagesz=1G), then we might not even
*have* a 2MB hstate so page_hstate() returns null and
copy_huge_page() oopses pretty fast since copy_huge_page()
dereferences the hstate:
void copy_huge_page(struct page *dst, struct page *src)
{
struct hstate *h = page_hstate(src);
if (unlikely(pages_per_huge_page(h) > MAX_ORDER_NR_PAGES)) {
...
Mel noticed that the migration code is really the only user of
these functions. This moves all the copy code over to migrate.c
and makes copy_huge_page() work for THP by checking for it
explicitly.
I believe the bug was introduced in b32967ff101:
Author: Mel Gorman <mgorman@...e.de>
Date: Mon Nov 19 12:35:47 2012 +0000
mm: numa: Add THP migration for the NUMA working set scanning fault case.
Signed-off-by: Dave Hansen <dave.hansen@...ux.intel.com>
---
linux.git-davehans/include/linux/hugetlb.h | 4 --
linux.git-davehans/mm/hugetlb.c | 34 --------------------
linux.git-davehans/mm/migrate.c | 48 +++++++++++++++++++++++++++++
3 files changed, 48 insertions(+), 38 deletions(-)
diff -puN mm/migrate.c~copy-huge-separate-from-copy-transhuge mm/migrate.c
--- linux.git/mm/migrate.c~copy-huge-separate-from-copy-transhuge 2013-11-15 14:44:55.256970259 -0800
+++ linux.git-davehans/mm/migrate.c 2013-11-15 14:45:17.457963844 -0800
@@ -442,6 +442,54 @@ int migrate_huge_page_move_mapping(struc
}
/*
+ * Gigantic pages are so large that the we do not guarantee
+ * that page++ pointer arithmetic will work across the
+ * entire page. We need something more specialized.
+ */
+static void __copy_gigantic_page(struct page *dst, struct page *src,
+ int nr_pages)
+{
+ int i;
+ struct page *dst_base = dst;
+ struct page *src_base = src;
+
+ for (i = 0; i < nr_pages; ) {
+ cond_resched();
+ copy_highpage(dst, src);
+
+ i++;
+ dst = mem_map_next(dst, dst_base, i);
+ src = mem_map_next(src, src_base, i);
+ }
+}
+
+static void copy_huge_page(struct page *dst, struct page *src)
+{
+ int i;
+ int nr_pages;
+
+ if (PageHuge(src)) {
+ /* hugetlbfs page */
+ struct hstate *h = page_hstate(src);
+ nr_pages = pages_per_huge_page(h);
+
+ if (unlikely(nr_pages > MAX_ORDER_NR_PAGES)) {
+ __copy_gigantic_page(dst, src, nr_pages);
+ return;
+ }
+ } else {
+ /* thp page */
+ BUG_ON(!PageTransHuge(src));
+ nr_pages = hpage_nr_pages(src);
+ }
+
+ for (i = 0; i < nr_pages; i++ ) {
+ cond_resched();
+ copy_highpage(dst + i, src + i);
+ }
+}
+
+/*
* Copy the page to its new location
*/
void migrate_page_copy(struct page *newpage, struct page *page)
diff -puN mm/hugetlb.c~copy-huge-separate-from-copy-transhuge mm/hugetlb.c
--- linux.git/mm/hugetlb.c~copy-huge-separate-from-copy-transhuge 2013-11-15 14:44:55.261970484 -0800
+++ linux.git-davehans/mm/hugetlb.c 2013-11-15 14:44:55.389976227 -0800
@@ -476,40 +476,6 @@ static int vma_has_reserves(struct vm_ar
return 0;
}
-static void copy_gigantic_page(struct page *dst, struct page *src)
-{
- int i;
- struct hstate *h = page_hstate(src);
- struct page *dst_base = dst;
- struct page *src_base = src;
-
- for (i = 0; i < pages_per_huge_page(h); ) {
- cond_resched();
- copy_highpage(dst, src);
-
- i++;
- dst = mem_map_next(dst, dst_base, i);
- src = mem_map_next(src, src_base, i);
- }
-}
-
-void copy_huge_page(struct page *dst, struct page *src)
-{
- int i;
- struct hstate *h = page_hstate(src);
-
- if (unlikely(pages_per_huge_page(h) > MAX_ORDER_NR_PAGES)) {
- copy_gigantic_page(dst, src);
- return;
- }
-
- might_sleep();
- for (i = 0; i < pages_per_huge_page(h); i++) {
- cond_resched();
- copy_highpage(dst + i, src + i);
- }
-}
-
static void enqueue_huge_page(struct hstate *h, struct page *page)
{
int nid = page_to_nid(page);
diff -puN include/linux/hugetlb.h~copy-huge-separate-from-copy-transhuge include/linux/hugetlb.h
--- linux.git/include/linux/hugetlb.h~copy-huge-separate-from-copy-transhuge 2013-11-15 14:44:55.263970574 -0800
+++ linux.git-davehans/include/linux/hugetlb.h 2013-11-15 14:44:55.325973356 -0800
@@ -69,7 +69,6 @@ int dequeue_hwpoisoned_huge_page(struct
bool isolate_huge_page(struct page *page, struct list_head *list);
void putback_active_hugepage(struct page *page);
bool is_hugepage_active(struct page *page);
-void copy_huge_page(struct page *dst, struct page *src);
#ifdef CONFIG_ARCH_WANT_HUGE_PMD_SHARE
pte_t *huge_pmd_share(struct mm_struct *mm, unsigned long addr, pud_t *pud);
@@ -140,9 +139,6 @@ static inline int dequeue_hwpoisoned_hug
#define isolate_huge_page(p, l) false
#define putback_active_hugepage(p) do {} while (0)
#define is_hugepage_active(x) false
-static inline void copy_huge_page(struct page *dst, struct page *src)
-{
-}
static inline unsigned long hugetlb_change_protection(struct vm_area_struct *vma,
unsigned long address, unsigned long end, pgprot_t newprot)
_
--
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