From: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>
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.
Signed-off-by: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>
---
linux.git-davehans/include/linux/huge_mm.h | 16 ++++++++++++++++
linux.git-davehans/mm/huge_memory.c | 13 +++++++++++++
linux.git-davehans/mm/migrate.c | 4 +++-
3 files changed, 32 insertions(+), 1 deletion(-)
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 2013-10-28 15:10:28.294220490 -0700
+++ linux.git-davehans/include/linux/huge_mm.h 2013-10-28 15:10:28.301220803 -0700
@@ -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 2013-10-28 15:10:28.296220580 -0700
+++ linux.git-davehans/mm/huge_memory.c 2013-10-28 15:10:28.302220848 -0700
@@ -2789,3 +2789,16 @@ 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;
+
+ might_sleep();
+ 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 2013-10-28 15:10:28.298220669 -0700
+++ linux.git-davehans/mm/migrate.c 2013-10-28 15:10:28.303220893 -0700
@@ -443,8 +443,10 @@ int migrate_huge_page_move_mapping(struc
*/
void migrate_page_copy(struct page *newpage, struct page *page)
{
- if (PageHuge(page) || PageTransHuge(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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