[HMM 02/15] mm/put_page: move ZONE_DEVICE page reference decrement v2

[Jérôme Glisse]

Move page reference decrement of ZONE_DEVICE from put_page()
to put_zone_device_page() this does not affect non ZONE_DEVICE
page.

Doing this allow to catch when a ZONE_DEVICE page refcount reach
1 which means the device is no longer reference by any one (unlike
page from other zone, ZONE_DEVICE page refcount never reach 0).

This patch is just a preparatory patch for HMM.

Changes since v1:
  - commit message

Signed-off-by: Jérôme Glisse 
Reviewed-by: Dan Williams 
Cc: Ross Zwisler 
---
 include/linux/mm.h | 14 +++---
 kernel/memremap.c  |  6 ++
 2 files changed, 17 insertions(+), 3 deletions(-)

diff --git a/include/linux/mm.h b/include/linux/mm.h
index c82e8db..022423c 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -821,11 +821,19 @@ static inline void put_page(struct page *page)
 {
page = compound_head(page);
 
+   /*
+* ZONE_DEVICE pages should never have their refcount reach 0 (this
+* would be a bug), so call page_ref_dec() in put_zone_device_page()
+* to decrement page refcount and skip __put_page() here, as this
+* would worsen things if a ZONE_DEVICE had a refcount bug.
+*/
+   if (unlikely(is_zone_device_page(page))) {
+   put_zone_device_page(page);
+   return;
+   }
+
if (put_page_testzero(page))
__put_page(page);
-
-   if (unlikely(is_zone_device_page(page)))
-   put_zone_device_page(page);
 }
 
 #if defined(CONFIG_SPARSEMEM) && !defined(CONFIG_SPARSEMEM_VMEMMAP)
diff --git a/kernel/memremap.c b/kernel/memremap.c
index ea714ee..97ef676 100644
--- a/kernel/memremap.c
+++ b/kernel/memremap.c
@@ -190,6 +190,12 @@ EXPORT_SYMBOL(get_zone_device_page);
 
 void put_zone_device_page(struct page *page)
 {
+   /*
+* ZONE_DEVICE page refcount should never reach 0 and never be freed
+* to kernel memory allocator.
+*/
+   page_ref_dec(page);
+
put_dev_pagemap(page->pgmap);
 }
 EXPORT_SYMBOL(put_zone_device_page);
-- 
2.9.3

[HMM 02/15] mm/put_page: move ZONE_DEVICE page reference decrement v2

[Jérôme Glisse]

Move page reference decrement of ZONE_DEVICE from put_page()
to put_zone_device_page() this does not affect non ZONE_DEVICE
page.

Doing this allow to catch when a ZONE_DEVICE page refcount reach
1 which means the device is no longer reference by any one (unlike
page from other zone, ZONE_DEVICE page refcount never reach 0).

This patch is just a preparatory patch for HMM.

Changes since v1:
  - commit message

Signed-off-by: Jérôme Glisse 
Reviewed-by: Dan Williams 
Cc: Ross Zwisler 
---
 include/linux/mm.h | 14 +++---
 kernel/memremap.c  |  6 ++
 2 files changed, 17 insertions(+), 3 deletions(-)

diff --git a/include/linux/mm.h b/include/linux/mm.h
index c82e8db..022423c 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -821,11 +821,19 @@ static inline void put_page(struct page *page)
 {
page = compound_head(page);
 
+   /*
+* ZONE_DEVICE pages should never have their refcount reach 0 (this
+* would be a bug), so call page_ref_dec() in put_zone_device_page()
+* to decrement page refcount and skip __put_page() here, as this
+* would worsen things if a ZONE_DEVICE had a refcount bug.
+*/
+   if (unlikely(is_zone_device_page(page))) {
+   put_zone_device_page(page);
+   return;
+   }
+
if (put_page_testzero(page))
__put_page(page);
-
-   if (unlikely(is_zone_device_page(page)))
-   put_zone_device_page(page);
 }
 
 #if defined(CONFIG_SPARSEMEM) && !defined(CONFIG_SPARSEMEM_VMEMMAP)
diff --git a/kernel/memremap.c b/kernel/memremap.c
index ea714ee..97ef676 100644
--- a/kernel/memremap.c
+++ b/kernel/memremap.c
@@ -190,6 +190,12 @@ EXPORT_SYMBOL(get_zone_device_page);
 
 void put_zone_device_page(struct page *page)
 {
+   /*
+* ZONE_DEVICE page refcount should never reach 0 and never be freed
+* to kernel memory allocator.
+*/
+   page_ref_dec(page);
+
put_dev_pagemap(page->pgmap);
 }
 EXPORT_SYMBOL(put_zone_device_page);
-- 
2.9.3

Re: [HMM 02/15] mm/put_page: move ZONE_DEVICE page reference decrement v2

[Dan Williams]

On Fri, Apr 21, 2017 at 8:30 PM, Jérôme Glisse  wrote:
> Move page reference decrement of ZONE_DEVICE from put_page()
> to put_zone_device_page() this does not affect non ZONE_DEVICE
> page.
>
> Doing this allow to catch when a ZONE_DEVICE page refcount reach
> 1 which means the device is no longer reference by any one (unlike
> page from other zone, ZONE_DEVICE page refcount never reach 0).
>
> This patch is just a preparatory patch for HMM.
>
> Changes since v1:
>   - commit message
>
> Signed-off-by: Jérôme Glisse 
> Cc: Dan Williams 
> Cc: Ross Zwisler 

Reviewed-by: Dan Williams 

Re: [HMM 02/15] mm/put_page: move ZONE_DEVICE page reference decrement v2

[Dan Williams]

On Fri, Apr 21, 2017 at 8:30 PM, Jérôme Glisse  wrote:
> Move page reference decrement of ZONE_DEVICE from put_page()
> to put_zone_device_page() this does not affect non ZONE_DEVICE
> page.
>
> Doing this allow to catch when a ZONE_DEVICE page refcount reach
> 1 which means the device is no longer reference by any one (unlike
> page from other zone, ZONE_DEVICE page refcount never reach 0).
>
> This patch is just a preparatory patch for HMM.
>
> Changes since v1:
>   - commit message
>
> Signed-off-by: Jérôme Glisse 
> Cc: Dan Williams 
> Cc: Ross Zwisler 

Reviewed-by: Dan Williams 

[HMM 02/15] mm/put_page: move ZONE_DEVICE page reference decrement v2

[Jérôme Glisse]

Move page reference decrement of ZONE_DEVICE from put_page()
to put_zone_device_page() this does not affect non ZONE_DEVICE
page.

Doing this allow to catch when a ZONE_DEVICE page refcount reach
1 which means the device is no longer reference by any one (unlike
page from other zone, ZONE_DEVICE page refcount never reach 0).

This patch is just a preparatory patch for HMM.

Changes since v1:
  - commit message

Signed-off-by: Jérôme Glisse 
Cc: Dan Williams 
Cc: Ross Zwisler 
---
 include/linux/mm.h | 14 +++---
 kernel/memremap.c  |  6 ++
 2 files changed, 17 insertions(+), 3 deletions(-)

diff --git a/include/linux/mm.h b/include/linux/mm.h
index c82e8db..022423c 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -821,11 +821,19 @@ static inline void put_page(struct page *page)
 {
page = compound_head(page);
 
+   /*
+* ZONE_DEVICE pages should never have their refcount reach 0 (this
+* would be a bug), so call page_ref_dec() in put_zone_device_page()
+* to decrement page refcount and skip __put_page() here, as this
+* would worsen things if a ZONE_DEVICE had a refcount bug.
+*/
+   if (unlikely(is_zone_device_page(page))) {
+   put_zone_device_page(page);
+   return;
+   }
+
if (put_page_testzero(page))
__put_page(page);
-
-   if (unlikely(is_zone_device_page(page)))
-   put_zone_device_page(page);
 }
 
 #if defined(CONFIG_SPARSEMEM) && !defined(CONFIG_SPARSEMEM_VMEMMAP)
diff --git a/kernel/memremap.c b/kernel/memremap.c
index ea714ee..97ef676 100644
--- a/kernel/memremap.c
+++ b/kernel/memremap.c
@@ -190,6 +190,12 @@ EXPORT_SYMBOL(get_zone_device_page);
 
 void put_zone_device_page(struct page *page)
 {
+   /*
+* ZONE_DEVICE page refcount should never reach 0 and never be freed
+* to kernel memory allocator.
+*/
+   page_ref_dec(page);
+
put_dev_pagemap(page->pgmap);
 }
 EXPORT_SYMBOL(put_zone_device_page);
-- 
2.9.3

[HMM 02/15] mm/put_page: move ZONE_DEVICE page reference decrement v2

[Jérôme Glisse]

Move page reference decrement of ZONE_DEVICE from put_page()
to put_zone_device_page() this does not affect non ZONE_DEVICE
page.

Doing this allow to catch when a ZONE_DEVICE page refcount reach
1 which means the device is no longer reference by any one (unlike
page from other zone, ZONE_DEVICE page refcount never reach 0).

This patch is just a preparatory patch for HMM.

Changes since v1:
  - commit message

Signed-off-by: Jérôme Glisse 
Cc: Dan Williams 
Cc: Ross Zwisler 
---
 include/linux/mm.h | 14 +++---
 kernel/memremap.c  |  6 ++
 2 files changed, 17 insertions(+), 3 deletions(-)

diff --git a/include/linux/mm.h b/include/linux/mm.h
index c82e8db..022423c 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -821,11 +821,19 @@ static inline void put_page(struct page *page)
 {
page = compound_head(page);
 
+   /*
+* ZONE_DEVICE pages should never have their refcount reach 0 (this
+* would be a bug), so call page_ref_dec() in put_zone_device_page()
+* to decrement page refcount and skip __put_page() here, as this
+* would worsen things if a ZONE_DEVICE had a refcount bug.
+*/
+   if (unlikely(is_zone_device_page(page))) {
+   put_zone_device_page(page);
+   return;
+   }
+
if (put_page_testzero(page))
__put_page(page);
-
-   if (unlikely(is_zone_device_page(page)))
-   put_zone_device_page(page);
 }
 
 #if defined(CONFIG_SPARSEMEM) && !defined(CONFIG_SPARSEMEM_VMEMMAP)
diff --git a/kernel/memremap.c b/kernel/memremap.c
index ea714ee..97ef676 100644
--- a/kernel/memremap.c
+++ b/kernel/memremap.c
@@ -190,6 +190,12 @@ EXPORT_SYMBOL(get_zone_device_page);
 
 void put_zone_device_page(struct page *page)
 {
+   /*
+* ZONE_DEVICE page refcount should never reach 0 and never be freed
+* to kernel memory allocator.
+*/
+   page_ref_dec(page);
+
put_dev_pagemap(page->pgmap);
 }
 EXPORT_SYMBOL(put_zone_device_page);
-- 
2.9.3