[PATCH 0/2] v2: fix hugetlb vs. anon-thp copy page

[PATCH 0/2] v2: fix hugetlb vs. anon-thp copy page

[Dave Hansen]

There were only minor comments about this the last time around.
Any reason not not merge it?

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[PATCH 1/2] mm: hugetlbfs: Add some VM_BUG_ON()s to catch non-hugetlbfs pages

[Dave Hansen]

From: Dave Hansen <dave.hansen@linux.intel.com>

Dave Jiang reported that he was seeing oopses when running
NUMA systems and default_hugepagesz=1G.  I traced the issue down
to migrate_page_copy() trying to use the same code for hugetlb
pages and transparent hugepages.  It should not have been trying
to pass thp pages in there.

So, add some VM_BUG_ON()s for the next hapless VM developer that
tries the same thing.

Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com>
Reviewed-by: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>

---

 linux.git-davehans/include/linux/hugetlb.h |    1 +
 linux.git-davehans/mm/hugetlb.c            |    1 +
 2 files changed, 2 insertions(+)

diff -puN include/linux/hugetlb.h~bug-not-hugetlbfs-in-copy_huge_page include/linux/hugetlb.h
--- linux.git/include/linux/hugetlb.h~bug-not-hugetlbfs-in-copy_huge_page	2013-11-14 15:09:38.707180957 -0800
+++ linux.git-davehans/include/linux/hugetlb.h	2013-11-14 15:09:38.710181090 -0800
@@ -355,6 +355,7 @@ static inline pte_t arch_make_huge_pte(p
 
 static inline struct hstate *page_hstate(struct page *page)
 {
+	VM_BUG_ON(!PageHuge(page));
 	return size_to_hstate(PAGE_SIZE << compound_order(page));
 }
 
diff -puN mm/hugetlb.c~bug-not-hugetlbfs-in-copy_huge_page mm/hugetlb.c
--- linux.git/mm/hugetlb.c~bug-not-hugetlbfs-in-copy_huge_page	2013-11-14 15:09:38.708181001 -0800
+++ linux.git-davehans/mm/hugetlb.c	2013-11-14 15:09:38.711181135 -0800
@@ -498,6 +498,7 @@ void copy_huge_page(struct page *dst, st
 	int i;
 	struct hstate *h = page_hstate(src);
 
+	VM_BUG_ON(!h);
 	if (unlikely(pages_per_huge_page(h) > MAX_ORDER_NR_PAGES)) {
 		copy_gigantic_page(dst, src);
 		return;
_

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Re: [PATCH 1/2] mm: hugetlbfs: Add some VM_BUG_ON()s to catch non-hugetlbfs pages

[Mel Gorman]

On Thu, Nov 14, 2013 at 03:33:58PM -0800, Dave Hansen wrote:
> 
> From: Dave Hansen <dave.hansen@linux.intel.com>
> 
> Dave Jiang reported that he was seeing oopses when running
> NUMA systems and default_hugepagesz=1G.  I traced the issue down
> to migrate_page_copy() trying to use the same code for hugetlb
> pages and transparent hugepages.  It should not have been trying
> to pass thp pages in there.
> 
> So, add some VM_BUG_ON()s for the next hapless VM developer that
> tries the same thing.
> 
> Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com>
> Reviewed-by: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
> 

Acked-by: Mel Gorman <mgorman@suse.de>

-- 
Mel Gorman
SUSE Labs

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[PATCH 2/2] mm: thp: give transparent hugepage code a separate copy_page

[Dave Hansen]

Changes from v1:
 * removed explicit might_sleep() in favor of the one that we
   get from the cond_resched();

--

From: Dave Hansen <dave.hansen@linux.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)) {
...

This patch creates a copy_high_order_page() which can
be used on THP pages.

I believe the bug was introduced in b32967ff101:
Author: Mel Gorman <mgorman@suse.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@linux.intel.com>
---

 linux.git-davehans/include/linux/huge_mm.h |   16 ++++++++++++++++
 linux.git-davehans/mm/huge_memory.c        |   12 ++++++++++++
 linux.git-davehans/mm/migrate.c            |    6 ++++--
 3 files changed, 32 insertions(+), 2 deletions(-)

diff -puN include/linux/huge_mm.h~copy-huge-separate-from-copy-transhuge include/linux/huge_mm.h
--- linux.git/include/linux/huge_mm.h~copy-huge-separate-from-copy-transhuge	2013-11-14 15:09:38.869188202 -0800
+++ linux.git-davehans/include/linux/huge_mm.h	2013-11-14 15:09:38.873188379 -0800
@@ -177,6 +177,10 @@ static inline struct page *compound_tran
 extern int do_huge_pmd_numa_page(struct mm_struct *mm, struct vm_area_struct *vma,
 				unsigned long addr, pmd_t pmd, pmd_t *pmdp);
 
+extern void copy_high_order_page(struct page *newpage,
+				 struct page *oldpage,
+				 int order);
+
 #else /* CONFIG_TRANSPARENT_HUGEPAGE */
 #define HPAGE_PMD_SHIFT ({ BUILD_BUG(); 0; })
 #define HPAGE_PMD_MASK ({ BUILD_BUG(); 0; })
@@ -227,6 +231,18 @@ static inline int do_huge_pmd_numa_page(
 	return 0;
 }
 
+/*
+ * The non-stub version of this code is probably usable
+ * generically but its only user is thp at the moment,
+ * so enforce that with a BUG()
+ */
+static inline  void copy_high_order_page(struct page *newpage,
+					 struct page *oldpage,
+					 int order)
+{
+	BUG();
+}
+
 #endif /* CONFIG_TRANSPARENT_HUGEPAGE */
 
 #endif /* _LINUX_HUGE_MM_H */
diff -puN mm/huge_memory.c~copy-huge-separate-from-copy-transhuge mm/huge_memory.c
--- linux.git/mm/huge_memory.c~copy-huge-separate-from-copy-transhuge	2013-11-14 15:09:38.870188245 -0800
+++ linux.git-davehans/mm/huge_memory.c	2013-11-14 15:09:38.874188424 -0800
@@ -2890,3 +2890,15 @@ void __vma_adjust_trans_huge(struct vm_a
 			split_huge_page_address(next->vm_mm, nstart);
 	}
 }
+
+void copy_high_order_page(struct page *newpage,
+			  struct page *oldpage,
+			  int order)
+{
+	int i;
+
+	for (i = 0; i < (1<<order); i++) {
+		cond_resched();
+		copy_highpage(newpage + i, oldpage + i);
+	}
+}
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	2013-11-14 15:09:38.871188288 -0800
+++ linux.git-davehans/mm/migrate.c	2013-11-14 15:09:38.874188424 -0800
@@ -447,8 +447,10 @@ void migrate_page_copy(struct page *newp
 {
 	int cpupid;
 
-	if (PageHuge(page) || PageTransHuge(page))
-		copy_huge_page(newpage, page);
+	if (PageHuge(page))
+ 		copy_huge_page(newpage, page);
+	else if(PageTransHuge(page))
+		copy_high_order_page(newpage, page, HPAGE_PMD_ORDER);
 	else
 		copy_highpage(newpage, page);
 
_

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Re: [PATCH 2/2] mm: thp: give transparent hugepage code a separate copy_page

[Mel Gorman]

On Thu, Nov 14, 2013 at 03:34:00PM -0800, Dave Hansen wrote:
> 
> Changes from v1:
>  * removed explicit might_sleep() in favor of the one that we
>    get from the cond_resched();
> 
> --
> 
> From: Dave Hansen <dave.hansen@linux.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)) {
> ...
> 
> This patch creates a copy_high_order_page() which can
> be used on THP pages.
> 
> I believe the bug was introduced in b32967ff101:
> Author: Mel Gorman <mgorman@suse.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@linux.intel.com>

It is a mild pity that there are variants of this like copy_user_huge_page
for COW. They could be collapsed but the result API would not be pretty.

A rename of copy_huge_page to copy_hugetlbfs_page is justified to avoid
a repeat mistake. Alternatively, there seems to be little reason to add
hugetlbfs and thp specific apis when you could just do something like this
(untested)

diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index 0b7656e..784313a 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -476,40 +476,6 @@ static int vma_has_reserves(struct vm_area_struct *vma, long chg)
 	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 --git a/mm/migrate.c b/mm/migrate.c
index 9167b22..843b96d 100644
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -440,6 +440,49 @@ int migrate_huge_page_move_mapping(struct address_space *mapping,
 	return MIGRATEPAGE_SUCCESS;
 }
 
+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);
+	}
+}
+
+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_PMD_NR;
+	}
+
+	for (i = 0; i < nr_pages; i++) {
+		cond_resched();
+		copy_highpage(dst + i, src + i);
+	}
+}
+
 /*
  * Copy the page to its new location
  */

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[PATCH 1/2] mm: hugetlbfs: Add some VM_BUG_ON()s to catch non-hugetlbfs pages

[Dave Hansen]

Dave Jiang reported that he was seeing oopses when running
NUMA systems and default_hugepagesz=1G.  I traced the issue down
to migrate_page_copy() trying to use the same code for hugetlb
pages and transparent hugepages.  It should not have been trying
to pass thp pages in there.

So, add some VM_BUG_ON()s for the next hapless VM developer that
tries the same thing.

---

 linux.git-davehans/include/linux/hugetlb.h |    1 +
 linux.git-davehans/mm/hugetlb.c            |    1 +
 2 files changed, 2 insertions(+)

diff -puN include/linux/hugetlb.h~bug-not-hugetlbfs-in-copy_huge_page include/linux/hugetlb.h
--- linux.git/include/linux/hugetlb.h~bug-not-hugetlbfs-in-copy_huge_page	2013-10-28 15:06:12.888828815 -0700
+++ linux.git-davehans/include/linux/hugetlb.h	2013-10-28 15:06:12.893829038 -0700
@@ -355,6 +355,7 @@ static inline pte_t arch_make_huge_pte(p
 
 static inline struct hstate *page_hstate(struct page *page)
 {
+	VM_BUG_ON(!PageHuge(page));
 	return size_to_hstate(PAGE_SIZE << compound_order(page));
 }
 
diff -puN mm/hugetlb.c~bug-not-hugetlbfs-in-copy_huge_page mm/hugetlb.c
--- linux.git/mm/hugetlb.c~bug-not-hugetlbfs-in-copy_huge_page	2013-10-28 15:06:12.890828904 -0700
+++ linux.git-davehans/mm/hugetlb.c	2013-10-28 15:06:12.894829082 -0700
@@ -498,6 +498,7 @@ void copy_huge_page(struct page *dst, st
 	int i;
 	struct hstate *h = page_hstate(src);
 
+	VM_BUG_ON(!h);
 	if (unlikely(pages_per_huge_page(h) > MAX_ORDER_NR_PAGES)) {
 		copy_gigantic_page(dst, src);
 		return;
_

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