The patch titled
Subject: mm, THP: add can_split_huge_page()
has been added to the -mm tree. Its filename is
mm-thp-add-can_split_huge_page.patch
This patch should soon appear at
http://ozlabs.org/~akpm/mmots/broken-out/mm-thp-add-can_split_huge_page.patch
and later at
http://ozlabs.org/~akpm/mmotm/broken-out/mm-thp-add-can_split_huge_page.patch
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------------------------------------------------------
From: Huang Ying <ying.huang@xxxxxxxxx>
Subject: mm, THP: add can_split_huge_page()
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.
Link: http://lkml.kernel.org/r/20170328053209.25876-8-ying.huang@xxxxxxxxx
Signed-off-by: "Huang, Ying" <ying.huang@xxxxxxxxx>
Acked-by: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
Cc: Andrea Arcangeli <aarcange@xxxxxxxxxx>
Cc: Ebru Akagunduz <ebru.akagunduz@xxxxxxxxx>
Cc: Hugh Dickins <hughd@xxxxxxxxxx>
Cc: Johannes Weiner <hannes@xxxxxxxxxxx>
Cc: Michal Hocko <mhocko@xxxxxxxxxx>
Cc: Minchan Kim <minchan@xxxxxxxxxx>
Cc: Rik van Riel <riel@xxxxxxxxxx>
Cc: Shaohua Li <shli@xxxxxxxxxx>
Cc: Tejun Heo <tj@xxxxxxxxxx>
Cc: Vladimir Davydov <vdavydov@xxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
include/linux/huge_mm.h | 7 +++++++
mm/huge_memory.c | 17 ++++++++++++++---
2 files changed, 21 insertions(+), 3 deletions(-)
diff -puN include/linux/huge_mm.h~mm-thp-add-can_split_huge_page include/linux/huge_mm.h
--- a/include/linux/huge_mm.h~mm-thp-add-can_split_huge_page
+++ a/include/linux/huge_mm.h
@@ -113,6 +113,7 @@ extern unsigned long thp_get_unmapped_ar
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 *pextra_pins);
int split_huge_page_to_list(struct page *page, struct list_head *list);
static inline int split_huge_page(struct page *page)
{
@@ -231,6 +232,12 @@ static inline void prep_transhuge_page(s
#define thp_get_unmapped_area NULL
+static inline bool
+can_split_huge_page(struct page *page, int *pextra_pins)
+{
+ BUILD_BUG();
+ return false;
+}
static inline int
split_huge_page_to_list(struct page *page, struct list_head *list)
{
diff -puN mm/huge_memory.c~mm-thp-add-can_split_huge_page mm/huge_memory.c
--- a/mm/huge_memory.c~mm-thp-add-can_split_huge_page
+++ a/mm/huge_memory.c
@@ -2367,6 +2367,19 @@ int page_trans_huge_mapcount(struct page
return ret;
}
+/* Racy check whether the huge page can be split */
+bool can_split_huge_page(struct page *page, int *pextra_pins)
+{
+ int extra_pins = 0;
+
+ /* Additional pins from radix tree */
+ if (!PageAnon(page))
+ extra_pins = HPAGE_PMD_NR;
+ if (pextra_pins)
+ *pextra_pins = extra_pins;
+ 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.
@@ -2426,8 +2439,6 @@ int split_huge_page_to_list(struct page
goto out;
}
- /* Addidional pins from radix tree */
- extra_pins = HPAGE_PMD_NR;
anon_vma = NULL;
i_mmap_lock_read(mapping);
}
@@ -2436,7 +2447,7 @@ int split_huge_page_to_list(struct page
* 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, &extra_pins)) {
ret = -EBUSY;
goto out_unlock;
}
_
Patches currently in -mm which might be from ying.huang@xxxxxxxxx are
mm-swap-fix-a-race-in-free_swap_and_cache.patch
mm-swap-fix-comment-in-__read_swap_cache_async.patch
mm-swap-improve-readability-via-make-spin_lock-unlock-balanced.patch
mm-swap-avoid-lock-swap_avail_lock-when-held-cluster-lock.patch
mm-swap-make-swap-cluster-size-same-of-thp-size-on-x86_64.patch
mm-memcg-support-to-charge-uncharge-multiple-swap-entries.patch
mm-thp-swap-add-swap-cluster-allocate-free-functions.patch
mm-thp-swap-add-get_huge_swap_page.patch
mm-thp-swap-support-to-clear-swap_has_cache-for-huge-page.patch
mm-thp-swap-support-to-add-delete-thp-to-from-swap-cache.patch
mm-thp-add-can_split_huge_page.patch
mm-thp-swap-support-to-split-thp-in-swap-cache.patch
mm-thp-swap-delay-splitting-thp-during-swap-out.patch
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