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Commit 30b0a105 authored by Dave Hansen's avatar Dave Hansen Committed by Linus Torvalds
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mm: thp: give transparent hugepage code a separate copy_page 



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 commit b32967ff ("mm: numa: Add
THP migration for the NUMA working set scanning fault case")

[akpm@linux-foundation.org: fix coding-style and comment text, per Naoya Horiguchi]
Signed-off-by: default avatarDave Hansen <dave.hansen@linux.intel.com>
Acked-by: default avatarMel Gorman <mgorman@suse.de>
Reviewed-by: default avatarNaoya Horiguchi <n-horiguchi@ah.jp.nec.com>
Cc: Hillf Danton <dhillf@gmail.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Tested-by: default avatarDave Jiang <dave.jiang@intel.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent c11230f4

include/linux/hugetlb.h

+0 −4
Original line number Diff line number Diff line
@@ -69,7 +69,6 @@ int dequeue_hwpoisoned_huge_page(struct page *page); 
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_huge_page(struct page *page) 
#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)

mm/hugetlb.c

+0 −34
Original line number Diff line number Diff line
@@ -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);

mm/migrate.c

+48 −0
Original line number Diff line number Diff line
@@ -441,6 +441,54 @@ int migrate_huge_page_move_mapping(struct address_space *mapping, 
	return MIGRATEPAGE_SUCCESS;

}



/*

 * Gigantic pages are so large that 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

 */