Re: [PATCH] mm:add VM_BUG_ON() for page_mapcount()

Re: [PATCH] mm:add VM_BUG_ON() for page_mapcount()

[Hillf Danton]

> 
> This patch add VM_BUG_ON() for slab page,
> because _mapcount is an union with slab struct in struct page,
> avoid access _mapcount if this page is a slab page.
> Also remove the unneeded bracket.
> 
> Signed-off-by: Yalin Wang <yalin.wang@sonymobile.com>
> ---
>  include/linux/mm.h | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/include/linux/mm.h b/include/linux/mm.h
> index 11b65cf..34124c4 100644
> --- a/include/linux/mm.h
> +++ b/include/linux/mm.h
> @@ -373,7 +373,8 @@ static inline void reset_page_mapcount(struct page *page)
> 
>  static inline int page_mapcount(struct page *page)
>  {
> -	return atomic_read(&(page)->_mapcount) + 1;
> +	VM_BUG_ON(PageSlab(page));

s/ VM_BUG_ON/ VM_BUG_ON_PAGE/ ?

> +	return atomic_read(&page->_mapcount) + 1;
>  }
> 

RE: [PATCH] mm:add VM_BUG_ON() for page_mapcount()

[Wang, Yalin]

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> -----Original Message-----
> From: Hillf Danton [mailto:hillf.zj@alibaba-inc.com]
> Sent: Monday, December 08, 2014 5:33 PM
> To: Wang, Yalin
> Cc: linux-kernel; linux-mm@kvack.org; linux-arm-kernel@lists.infradead.org;
> Andrew Morton; Hillf Danton
> Subject: Re: [PATCH] mm:add VM_BUG_ON() for page_mapcount()
> 
> >
> > This patch add VM_BUG_ON() for slab page, because _mapcount is an
> > union with slab struct in struct page, avoid access _mapcount if this
> > page is a slab page.
> > Also remove the unneeded bracket.
> >
> > Signed-off-by: Yalin Wang <yalin.wang@sonymobile.com>
> > ---
> >  include/linux/mm.h | 3 ++-
> >  1 file changed, 2 insertions(+), 1 deletion(-)
> >
> > diff --git a/include/linux/mm.h b/include/linux/mm.h index
> > 11b65cf..34124c4 100644
> > --- a/include/linux/mm.h
> > +++ b/include/linux/mm.h
> > @@ -373,7 +373,8 @@ static inline void reset_page_mapcount(struct page
> > *page)
> >
> >  static inline int page_mapcount(struct page *page)  {
> > -	return atomic_read(&(page)->_mapcount) + 1;
> > +	VM_BUG_ON(PageSlab(page));
> 
> s/ VM_BUG_ON/ VM_BUG_ON_PAGE/ ?
Yes, I will send again .
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[PATCH V2] mm:add VM_BUG_ON() for page_mapcount()

[Wang, Yalin]

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This patch add VM_BUG_ON_PAGE() for slab page,
because _mapcount is an union with slab struct in struct page,
avoid access _mapcount if this page is a slab page.
Also remove the unneeded bracket.

Signed-off-by: Yalin Wang <yalin.wang@sonymobile.com>
---
 include/linux/mm.h | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/include/linux/mm.h b/include/linux/mm.h
index b464611..a117527 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -449,7 +449,8 @@ static inline void page_mapcount_reset(struct page *page)
 
 static inline int page_mapcount(struct page *page)
 {
-	return atomic_read(&(page)->_mapcount) + 1;
+	VM_BUG_ON_PAGE(PageSlab(page), page);
+	return atomic_read(&page->_mapcount) + 1;
 }
 
 static inline int page_count(struct page *page)
-- 
2.1.3
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[PATCH V3] mm:add VM_BUG_ON_PAGE() for page_mapcount()

[Wang, Yalin]

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This patch add VM_BUG_ON_PAGE() for slab page,
because _mapcount is an union with slab struct in struct page,
avoid access _mapcount if this page is a slab page.
Also remove the unneeded bracket.

Signed-off-by: Yalin Wang <yalin.wang@sonymobile.com>
---
 include/linux/mm.h | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/include/linux/mm.h b/include/linux/mm.h
index b464611..a117527 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -449,7 +449,8 @@ static inline void page_mapcount_reset(struct page *page)
 
 static inline int page_mapcount(struct page *page)
 {
-	return atomic_read(&(page)->_mapcount) + 1;
+	VM_BUG_ON_PAGE(PageSlab(page), page);
+	return atomic_read(&page->_mapcount) + 1;
 }
 
 static inline int page_count(struct page *page)
-- 
2.1.3
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Re: [PATCH V3] mm:add VM_BUG_ON_PAGE() for page_mapcount()

[Kirill A. Shutemov]

On Mon, Dec 08, 2014 at 05:59:46PM +0800, Wang, Yalin wrote:
> This patch add VM_BUG_ON_PAGE() for slab page,
> because _mapcount is an union with slab struct in struct page,
> avoid access _mapcount if this page is a slab page.
> Also remove the unneeded bracket.
> 
> Signed-off-by: Yalin Wang <yalin.wang@sonymobile.com>

Acked-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
-- 
 Kirill A. Shutemov

Re: [PATCH V3] mm:add VM_BUG_ON_PAGE() for page_mapcount()

[Hillf Danton]

> 
> This patch add VM_BUG_ON_PAGE() for slab page,
> because _mapcount is an union with slab struct in struct page,
> avoid access _mapcount if this page is a slab page.
> Also remove the unneeded bracket.
> 
> Signed-off-by: Yalin Wang <yalin.wang@sonymobile.com>
> ---
Acked-by: Hillf Danton <hillf.zj@alibaba-inc.com>

>  include/linux/mm.h | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/include/linux/mm.h b/include/linux/mm.h
> index b464611..a117527 100644
> --- a/include/linux/mm.h
> +++ b/include/linux/mm.h
> @@ -449,7 +449,8 @@ static inline void page_mapcount_reset(struct page *page)
> 
>  static inline int page_mapcount(struct page *page)
>  {
> -	return atomic_read(&(page)->_mapcount) + 1;
> +	VM_BUG_ON_PAGE(PageSlab(page), page);
> +	return atomic_read(&page->_mapcount) + 1;
>  }
> 
>  static inline int page_count(struct page *page)
> --
> 2.1.3

Re: [PATCH V3] mm:add VM_BUG_ON_PAGE() for page_mapcount()

[Vlastimil Babka]

On 12/08/2014 10:59 AM, Wang, Yalin wrote:
> This patch add VM_BUG_ON_PAGE() for slab page,
> because _mapcount is an union with slab struct in struct page,
> avoid access _mapcount if this page is a slab page.
> Also remove the unneeded bracket.
>
> Signed-off-by: Yalin Wang <yalin.wang@sonymobile.com>
> ---
>   include/linux/mm.h | 3 ++-
>   1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/include/linux/mm.h b/include/linux/mm.h
> index b464611..a117527 100644
> --- a/include/linux/mm.h
> +++ b/include/linux/mm.h
> @@ -449,7 +449,8 @@ static inline void page_mapcount_reset(struct page *page)
>
>   static inline int page_mapcount(struct page *page)
>   {
> -	return atomic_read(&(page)->_mapcount) + 1;
> +	VM_BUG_ON_PAGE(PageSlab(page), page);
> +	return atomic_read(&page->_mapcount) + 1;
>   }
>

I think this might theoretically trigger on the following code in 
compaction's isolate_migratepages_block():

/*
   * Migration will fail if an anonymous page is pinned in memory,
   * so avoid taking lru_lock and isolating it unnecessarily in an
   * admittedly racy check.
   */
if (!page_mapping(page) &&
     page_count(page) > page_mapcount(page))
	continue;

This is done after PageLRU() was positive, but the lru_lock might be not 
taken yet. So, there's some time window during which the page might have 
been reclaimed from LRU and become a PageSlab(page). !page_mapping(page) 
will be true in that case so it will proceed with page_mapcount(page) 
test and trigger the VM_BUG_ON.

(That test was added by DavidR year ago in commit 
119d6d59dcc0980dcd581fdadb6b2033b512a473)

Vlastimil





>   static inline int page_count(struct page *page)
>

[RFC] mm:add KPF_ZERO_PAGE flag for /proc/kpageflags

[Wang, Yalin]

This patch add KPF_ZERO_PAGE flag for zero_page,
so that userspace process can notice zero_page from
/proc/kpageflags, and then do memory analysis more accurately.

Signed-off-by: Yalin Wang <yalin.wang@sonymobile.com>
---
 fs/proc/page.c                         | 3 +++
 include/uapi/linux/kernel-page-flags.h | 1 +
 2 files changed, 4 insertions(+)

diff --git a/fs/proc/page.c b/fs/proc/page.c
index 1e3187d..120dbf7 100644
--- a/fs/proc/page.c
+++ b/fs/proc/page.c
@@ -136,6 +136,9 @@ u64 stable_page_flags(struct page *page)
 	if (PageBalloon(page))
 		u |= 1 << KPF_BALLOON;
 
+	if (is_zero_pfn(page_to_pfn(page)))
+		u |= 1 << KPF_ZERO_PAGE;
+
 	u |= kpf_copy_bit(k, KPF_LOCKED,	PG_locked);
 
 	u |= kpf_copy_bit(k, KPF_SLAB,		PG_slab);
diff --git a/include/uapi/linux/kernel-page-flags.h b/include/uapi/linux/kernel-page-flags.h
index 2f96d23..a6c4962 100644
--- a/include/uapi/linux/kernel-page-flags.h
+++ b/include/uapi/linux/kernel-page-flags.h
@@ -32,6 +32,7 @@
 #define KPF_KSM			21
 #define KPF_THP			22
 #define KPF_BALLOON		23
+#define KPF_ZERO_PAGE		24
 
 
 #endif /* _UAPILINUX_KERNEL_PAGE_FLAGS_H */
-- 
2.1.3

[RFC V2] mm:add KPF_ZERO_PAGE flag for /proc/kpageflags

[Wang, Yalin]

This patch add KPF_ZERO_PAGE flag for zero_page,
so that userspace process can notice zero_page from
/proc/kpageflags, and then do memory analysis more accurately.

Signed-off-by: Yalin Wang <yalin.wang@sonymobile.com>
---
 fs/proc/page.c                         | 14 +++++++++++---
 include/linux/huge_mm.h                | 12 ++++++++++++
 include/uapi/linux/kernel-page-flags.h |  1 +
 mm/huge_memory.c                       |  7 +------
 4 files changed, 25 insertions(+), 9 deletions(-)

diff --git a/fs/proc/page.c b/fs/proc/page.c
index 1e3187d..dbe5630 100644
--- a/fs/proc/page.c
+++ b/fs/proc/page.c
@@ -5,6 +5,7 @@
 #include <linux/ksm.h>
 #include <linux/mm.h>
 #include <linux/mmzone.h>
+#include <linux/huge_mm.h>
 #include <linux/proc_fs.h>
 #include <linux/seq_file.h>
 #include <linux/hugetlb.h>
@@ -121,9 +122,16 @@ u64 stable_page_flags(struct page *page)
 	 * just checks PG_head/PG_tail, so we need to check PageLRU/PageAnon
 	 * to make sure a given page is a thp, not a non-huge compound page.
 	 */
-	else if (PageTransCompound(page) && (PageLRU(compound_head(page)) ||
-					     PageAnon(compound_head(page))))
-		u |= 1 << KPF_THP;
+	else if (PageTransCompound(page)) {
+		struct page *head = compound_head(page);
+
+		if (PageLRU(head) || PageAnon(head))
+			u |= 1 << KPF_THP;
+		else if (is_huge_zero_page(head))
+			u |= 1 << KPF_ZERO_PAGE;
+	} else if (is_zero_pfn(page_to_pfn(page)))
+		u |= 1 << KPF_ZERO_PAGE;
+
 
 	/*
 	 * Caveats on high order pages: page->_count will only be set
diff --git a/include/linux/huge_mm.h b/include/linux/huge_mm.h
index ad9051b..f10b20f 100644
--- a/include/linux/huge_mm.h
+++ b/include/linux/huge_mm.h
@@ -157,6 +157,13 @@ static inline int hpage_nr_pages(struct page *page)
 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 struct page *huge_zero_page;
+
+static inline bool is_huge_zero_page(struct page *page)
+{
+	return ACCESS_ONCE(huge_zero_page) == page;
+}
+
 #else /* CONFIG_TRANSPARENT_HUGEPAGE */
 #define HPAGE_PMD_SHIFT ({ BUILD_BUG(); 0; })
 #define HPAGE_PMD_MASK ({ BUILD_BUG(); 0; })
@@ -206,6 +213,11 @@ static inline int do_huge_pmd_numa_page(struct mm_struct *mm, struct vm_area_str
 	return 0;
 }
 
+static inline bool is_huge_zero_page(struct page *page)
+{
+	return false;
+}
+
 #endif /* CONFIG_TRANSPARENT_HUGEPAGE */
 
 #endif /* _LINUX_HUGE_MM_H */
diff --git a/include/uapi/linux/kernel-page-flags.h b/include/uapi/linux/kernel-page-flags.h
index 2f96d23..a6c4962 100644
--- a/include/uapi/linux/kernel-page-flags.h
+++ b/include/uapi/linux/kernel-page-flags.h
@@ -32,6 +32,7 @@
 #define KPF_KSM			21
 #define KPF_THP			22
 #define KPF_BALLOON		23
+#define KPF_ZERO_PAGE		24
 
 
 #endif /* _UAPILINUX_KERNEL_PAGE_FLAGS_H */
diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index de98415..d7bc7a5 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -171,12 +171,7 @@ static int start_khugepaged(void)
 }
 
 static atomic_t huge_zero_refcount;
-static struct page *huge_zero_page __read_mostly;
-
-static inline bool is_huge_zero_page(struct page *page)
-{
-	return ACCESS_ONCE(huge_zero_page) == page;
-}
+struct page *huge_zero_page __read_mostly;
 
 static inline bool is_huge_zero_pmd(pmd_t pmd)
 {
-- 
2.1.3

[PATCH] mm:add VM_BUG_ON() for page_mapcount()

[Wang, Yalin]

This patch add VM_BUG_ON() for slab page,
because _mapcount is an union with slab struct in struct page,
avoid access _mapcount if this page is a slab page.
Also remove the unneeded bracket.

Signed-off-by: Yalin Wang <yalin.wang@sonymobile.com>
---
 include/linux/mm.h | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/include/linux/mm.h b/include/linux/mm.h
index 11b65cf..34124c4 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -373,7 +373,8 @@ static inline void reset_page_mapcount(struct page *page)
 
 static inline int page_mapcount(struct page *page)
 {
-	return atomic_read(&(page)->_mapcount) + 1;
+	VM_BUG_ON(PageSlab(page));
+	return atomic_read(&page->_mapcount) + 1;
 }
 
 static inline int page_count(struct page *page)
-- 
2.1.3

Re: [PATCH] mm:add VM_BUG_ON() for page_mapcount()

[Kirill A. Shutemov]

On Mon, Dec 08, 2014 at 03:47:47PM +0800, Wang, Yalin wrote:
> This patch add VM_BUG_ON() for slab page,
> because _mapcount is an union with slab struct in struct page,
> avoid access _mapcount if this page is a slab page.
> Also remove the unneeded bracket.
> 
> Signed-off-by: Yalin Wang <yalin.wang@sonymobile.com>
> ---
>  include/linux/mm.h | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/include/linux/mm.h b/include/linux/mm.h
> index 11b65cf..34124c4 100644
> --- a/include/linux/mm.h
> +++ b/include/linux/mm.h
> @@ -373,7 +373,8 @@ static inline void reset_page_mapcount(struct page *page)
>  
>  static inline int page_mapcount(struct page *page)
>  {
> -	return atomic_read(&(page)->_mapcount) + 1;
> +	VM_BUG_ON(PageSlab(page));

VM_BUG_ON_PAGE(), please.

-- 
 Kirill A. Shutemov