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Message-Id: <20161028055608.1736-8-ying.huang@intel.com>
Date: Fri, 28 Oct 2016 13:56:06 +0800
From: "Huang, Ying" <ying.huang@...el.com>
To: Andrew Morton <akpm@...ux-foundation.org>
Cc: tim.c.chen@...el.com, dave.hansen@...el.com, andi.kleen@...el.com,
aaron.lu@...el.com, linux-mm@...ck.org,
linux-kernel@...r.kernel.org, Huang Ying <ying.huang@...el.com>,
Andrea Arcangeli <aarcange@...hat.com>,
"Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>,
Ebru Akagunduz <ebru.akagunduz@...il.com>
Subject: [PATCH -v4 RESEND 7/9] mm, THP: Add can_split_huge_page()
From: Huang Ying <ying.huang@...el.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@...hat.com>
Cc: Kirill A. Shutemov <kirill.shutemov@...ux.intel.com>
Cc: Ebru Akagunduz <ebru.akagunduz@...il.com>
Signed-off-by: "Huang, Ying" <ying.huang@...el.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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