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Groups > linux.kernel > #1510867

[PATCH -v4 RESEND 7/9] mm, THP: Add can_split_huge_page()

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From: Huang Ying <ying.huang@intel.com>

Separates checking whether we can split the huge page from
split_huge_page_to_list() into a function.  This will help to check that
before splitting the THP (Transparent Huge Page) really.

This will be used for delaying splitting THP during swapping out.  Where
for a THP, we will allocate a swap cluster, add the THP into the swap
cache, then split the THP.  To avoid the unnecessary operations for the
un-splittable THP, we will check that firstly.

There is no functionality change in this patch.

Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Cc: Ebru Akagunduz <ebru.akagunduz@gmail.com>
Signed-off-by: "Huang, Ying" <ying.huang@intel.com>
---
 include/linux/huge_mm.h |  7 +++++++
 mm/huge_memory.c        | 13 ++++++++++++-
 2 files changed, 19 insertions(+), 1 deletion(-)

diff --git a/include/linux/huge_mm.h b/include/linux/huge_mm.h
index 9b9f65d..14ffa3f 100644
--- a/include/linux/huge_mm.h
+++ b/include/linux/huge_mm.h
@@ -94,6 +94,7 @@ extern unsigned long thp_get_unmapped_area(struct file *filp,
 extern void prep_transhuge_page(struct page *page);
 extern void free_transhuge_page(struct page *page);
 
+bool can_split_huge_page(struct page *page);
 int split_huge_page_to_list(struct page *page, struct list_head *list);
 static inline int split_huge_page(struct page *page)
 {
@@ -176,6 +177,12 @@ static inline void prep_transhuge_page(struct page *page) {}
 
 #define thp_get_unmapped_area	NULL
 
+static inline bool
+can_split_huge_page(struct page *page)
+{
+	BUILD_BUG();
+	return false;
+}
 static inline int
 split_huge_page_to_list(struct page *page, struct list_head *list)
 {
diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index cdcd25c..326b145 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -2013,6 +2013,17 @@ int page_trans_huge_mapcount(struct page *page, int *total_mapcount)
 	return ret;
 }
 
+/* Racy check whether the huge page can be split */
+bool can_split_huge_page(struct page *page)
+{
+	int extra_pins = 0;
+
+	/* Additional pins from radix tree */
+	if (!PageAnon(page))
+		extra_pins = HPAGE_PMD_NR;
+	return total_mapcount(page) == page_count(page) - extra_pins - 1;
+}
+
 /*
  * This function splits huge page into normal pages. @page can point to any
  * subpage of huge page to split. Split doesn't change the position of @page.
@@ -2083,7 +2094,7 @@ int split_huge_page_to_list(struct page *page, struct list_head *list)
 	 * Racy check if we can split the page, before freeze_page() will
 	 * split PMDs
 	 */
-	if (total_mapcount(head) != page_count(head) - extra_pins - 1) {
+	if (!can_split_huge_page(head)) {
 		ret = -EBUSY;
 		goto out_unlock;
 	}
-- 
2.9.3

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Thread

[PATCH -v4 RESEND 0/9] THP swap: Delay splitting THP during swapping out "Huang, Ying" <ying.huang@intel.com> - 2016-10-28 08:00 +0200
  [PATCH -v4 RESEND 5/9] mm, THP, swap: Support to clear SWAP_HAS_CACHE for huge page "Huang, Ying" <ying.huang@intel.com> - 2016-10-28 08:00 +0200
  [PATCH -v4 RESEND 9/9] mm, THP, swap: Delay splitting THP during swap out "Huang, Ying" <ying.huang@intel.com> - 2016-10-28 08:00 +0200
  [PATCH -v4 RESEND 6/9] mm, THP, swap: Support to add/delete THP to/from swap cache "Huang, Ying" <ying.huang@intel.com> - 2016-10-28 08:00 +0200
    Re: [PATCH -v4 RESEND 6/9] mm, THP, swap: Support to add/delete THP to/from swap cache "Hillf Danton" <hillf.zj@alibaba-inc.com> - 2016-10-28 10:20 +0200
      Re: [PATCH -v4 RESEND 6/9] mm, THP, swap: Support to add/delete THP to/from swap cache "Huang\, Ying" <ying.huang@intel.com> - 2016-10-28 10:40 +0200
  [PATCH -v4 RESEND 8/9] mm, THP, swap: Support to split THP in swap cache "Huang, Ying" <ying.huang@intel.com> - 2016-10-28 08:00 +0200
    Re: [PATCH -v4 RESEND 8/9] mm, THP, swap: Support to split THP in swap cache "Hillf Danton" <hillf.zj@alibaba-inc.com> - 2016-10-28 12:20 +0200
      Re: [PATCH -v4 RESEND 8/9] mm, THP, swap: Support to split THP in swap cache "Huang\, Ying" <ying.huang@intel.com> - 2016-10-31 02:30 +0100
  [PATCH -v4 RESEND 4/9] mm, THP, swap: Add get_huge_swap_page() "Huang, Ying" <ying.huang@intel.com> - 2016-10-28 08:00 +0200
  [PATCH -v4 RESEND 1/9] mm, swap: Make swap cluster size same of THP size on x86_64 "Huang, Ying" <ying.huang@intel.com> - 2016-10-28 08:00 +0200
  [PATCH -v4 RESEND 3/9] mm, THP, swap: Add swap cluster allocate/free functions "Huang, Ying" <ying.huang@intel.com> - 2016-10-28 08:00 +0200
  [PATCH -v4 RESEND 7/9] mm, THP: Add can_split_huge_page() "Huang, Ying" <ying.huang@intel.com> - 2016-10-28 08:00 +0200
  [PATCH -v4 RESEND 2/9] mm, memcg: Support to charge/uncharge multiple swap entries "Huang, Ying" <ying.huang@intel.com> - 2016-10-28 08:10 +0200

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