On Fri, 6 May 2016 17:03:58 +0200 Andrea Arcangeli <[email protected]> wrote:
> This will provide fully accuracy to the mapcount calculation in the
> write protect faults, so page pinning will not get broken by false
> positive copy-on-writes.
>
> total_mapcount() isn't the right calculation needed in
> reuse_swap_page(), so this introduces a page_trans_huge_mapcount()
> that is effectively the full accurate return value for page_mapcount()
> if dealing with Transparent Hugepages, however we only use the
> page_trans_huge_mapcount() during COW faults where it strictly needed,
> due to its higher runtime cost.
>
> This also provide at practical zero cost the total_mapcount
> information which is needed to know if we can still relocate the page
> anon_vma to the local vma. If page_trans_huge_mapcount() returns 1 we
> can reuse the page no matter if it's a pte or a pmd_trans_huge
> triggering the fault, but we can only relocate the page anon_vma to
> the local vma->anon_vma if we're sure it's only this "vma" mapping the
> whole THP physical range.
>
> Kirill A. Shutemov discovered the problem with moving the page
> anon_vma to the local vma->anon_vma in a previous version of this
> patch and another problem in the way page_move_anon_rmap() was called.
x86_64 allnoconfig:
include/linux/swap.h: In function 'reuse_swap_page':
include/linux/swap.h:518: error: implicit declaration of function
'page_trans_huge_mapcount'
In file included from include/linux/suspend.h:8,
from arch/x86/kernel/asm-offsets.c:12:
include/linux/mm.h: At top level:
include/linux/mm.h:509: error: static declaration of 'page_trans_huge_mapcount'
follows non-static declaration
include/linux/swap.h:518: note: previous implicit declaration of
'page_trans_huge_mapcount' was here
include ordering I assume. mm.h vs swap.h.
I did the below (whcih is a bit dumb) but got
mm/built-in.o: In function `do_wp_page':
memory.c:(.text+0x194b3): undefined reference to `page_trans_huge_mapcount'
and gave up.
From: Andrew Morton <[email protected]>
Subject:
mm-thp-calculate-the-mapcount-correctly-for-thp-pages-during-wp-faults-fix
Cc: "Kirill A. Shutemov" <[email protected]>
Cc: <[email protected]> [4.5]
Cc: Alex Williamson <[email protected]>
Cc: Andrea Arcangeli <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
---
include/linux/mm.h | 10 +---------
include/linux/swap.h | 2 ++
mm/huge_memory.c | 12 ++++++++++++
3 files changed, 15 insertions(+), 9 deletions(-)
---
a/include/linux/mm.h~mm-thp-calculate-the-mapcount-correctly-for-thp-pages-during-wp-faults-fix
+++ a/include/linux/mm.h
@@ -500,21 +500,13 @@ static inline int page_mapcount(struct p
#ifdef CONFIG_TRANSPARENT_HUGEPAGE
int total_mapcount(struct page *page);
-int page_trans_huge_mapcount(struct page *page, int *total_mapcount);
#else
static inline int total_mapcount(struct page *page)
{
return page_mapcount(page);
}
-static inline int page_trans_huge_mapcount(struct page *page,
- int *total_mapcount)
-{
- int mapcount = page_mapcount(page);
- if (total_mapcount)
- *total_mapcount = mapcount;
- return mapcount;
-}
#endif
+int page_trans_huge_mapcount(struct page *page, int *total_mapcount);
static inline struct page *virt_to_head_page(const void *x)
{
---
a/include/linux/swap.h~mm-thp-calculate-the-mapcount-correctly-for-thp-pages-during-wp-faults-fix
+++ a/include/linux/swap.h
@@ -248,6 +248,8 @@ struct swap_info_struct {
struct swap_cluster_info discard_cluster_tail; /* list tail of discard
clusters */
};
+int page_trans_huge_mapcount(struct page *page, int *total_mapcount);
+
/* linux/mm/workingset.c */
void *workingset_eviction(struct address_space *mapping, struct page *page);
bool workingset_refault(void *shadow);
---
a/mm/huge_memory.c~mm-thp-calculate-the-mapcount-correctly-for-thp-pages-during-wp-faults-fix
+++ a/mm/huge_memory.c
@@ -3217,6 +3217,7 @@ int total_mapcount(struct page *page)
return ret;
}
+#ifdef CONFIG_TRANSPARENT_HUGEPAGE
/*
* This calculates accurately how many mappings a transparent hugepage
* has (unlike page_mapcount() which isn't fully accurate). This full
@@ -3271,6 +3272,17 @@ int page_trans_huge_mapcount(struct page
return ret;
}
+#else
+
+int page_trans_huge_mapcount(struct page *page, int *total_mapcount)
+{
+ int mapcount = page_mapcount(page);
+ if (total_mapcount)
+ *total_mapcount = mapcount;
+ return mapcount;
+}
+#endif
+
/*
* 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.
