Re: [PATCH 5/8] mm: simplify freeing of devmap managed pages

[Chaitanya Kulkarni]

> -static inline bool page_is_devmap_managed(struct page *page)
> +bool __put_devmap_managed_page(struct page *page);
> +static inline bool put_devmap_managed_page(struct page *page)
>   {
>   if (!static_branch_unlikely(_managed_key))
>   return false;
>   if (!is_zone_device_page(page))
>   return false;
> - switch (page->pgmap->type) {
> - case MEMORY_DEVICE_PRIVATE:
> - case MEMORY_DEVICE_FS_DAX:
> - return true;
> - default:
> - break;
> - }

nit:- how some variant of following to makes all cases evident
without having to look into memremap.h for other enum values ?

 switch (page->pgmap->type) {
 case MEMORY_DEVICE_PRIVATE:
 case MEMORY_DEVICE_FS_DAX:
 return __put_devmap_managed_page(page);
 case MEMORY_DEVICE_GENERIC:
 case MEMORY_DEVICE_PCI_P2PDMA:
 return false;
 default:
 WARN_ON_ONCE(1);
 return false;
 }


> - return false;
> + if (page->pgmap->type != MEMORY_DEVICE_PRIVATE &&
> + page->pgmap->type != MEMORY_DEVICE_FS_DAX)
> + return false;
> + return __put_devmap_managed_page(page);

nit:- we are only returning true value from __put_devmap_managed_page()
in this patch. Perhaps make it __put_dev_map_managed_page()
return void and return true from above ?

or maybe someone can send a cleanup once this is merged.

>   }
>   

Irrespective of above comment(s), looks good.

Reviewed-by: Chaitanya Kulkarni 

Re: [PATCH 5/8] mm: simplify freeing of devmap managed pages

[Dan Williams]

On Sun, Feb 6, 2022 at 10:33 PM Christoph Hellwig  wrote:
>
> Make put_devmap_managed_page return if it took charge of the page
> or not and remove the separate page_is_devmap_managed helper.

Looks good to me:

Reviewed-by: Dan Williams 

Re: [PATCH 5/8] mm: simplify freeing of devmap managed pages

[Jason Gunthorpe]

On Mon, Feb 07, 2022 at 07:32:46AM +0100, Christoph Hellwig wrote:
> Make put_devmap_managed_page return if it took charge of the page
> or not and remove the separate page_is_devmap_managed helper.
> 
> Signed-off-by: Christoph Hellwig 
> ---
>  include/linux/mm.h | 34 ++
>  mm/memremap.c  | 20 +---
>  mm/swap.c  | 10 +-
>  3 files changed, 20 insertions(+), 44 deletions(-)

Reviewed-by: Jason Gunthorpe 

Jason

[PATCH 5/8] mm: simplify freeing of devmap managed pages

[Christoph Hellwig]

Make put_devmap_managed_page return if it took charge of the page
or not and remove the separate page_is_devmap_managed helper.

Signed-off-by: Christoph Hellwig 
---
 include/linux/mm.h | 34 ++
 mm/memremap.c  | 20 +---
 mm/swap.c  | 10 +-
 3 files changed, 20 insertions(+), 44 deletions(-)

diff --git a/include/linux/mm.h b/include/linux/mm.h
index 91dd0bc786a9ec..26baadcef4556b 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -1094,33 +1094,24 @@ static inline bool is_zone_movable_page(const struct 
page *page)
 #ifdef CONFIG_DEV_PAGEMAP_OPS
 DECLARE_STATIC_KEY_FALSE(devmap_managed_key);
 
-static inline bool page_is_devmap_managed(struct page *page)
+bool __put_devmap_managed_page(struct page *page);
+static inline bool put_devmap_managed_page(struct page *page)
 {
if (!static_branch_unlikely(_managed_key))
return false;
if (!is_zone_device_page(page))
return false;
-   switch (page->pgmap->type) {
-   case MEMORY_DEVICE_PRIVATE:
-   case MEMORY_DEVICE_FS_DAX:
-   return true;
-   default:
-   break;
-   }
-   return false;
+   if (page->pgmap->type != MEMORY_DEVICE_PRIVATE &&
+   page->pgmap->type != MEMORY_DEVICE_FS_DAX)
+   return false;
+   return __put_devmap_managed_page(page);
 }
 
-void put_devmap_managed_page(struct page *page);
-
 #else /* CONFIG_DEV_PAGEMAP_OPS */
-static inline bool page_is_devmap_managed(struct page *page)
+static inline bool put_devmap_managed_page(struct page *page)
 {
return false;
 }
-
-static inline void put_devmap_managed_page(struct page *page)
-{
-}
 #endif /* CONFIG_DEV_PAGEMAP_OPS */
 
 static inline bool is_device_private_page(const struct page *page)
@@ -1220,16 +1211,11 @@ static inline void put_page(struct page *page)
struct folio *folio = page_folio(page);
 
/*
-* For devmap managed pages we need to catch refcount transition from
-* 2 to 1, when refcount reach one it means the page is free and we
-* need to inform the device driver through callback. See
-* include/linux/memremap.h and HMM for details.
+* For some devmap managed pages we need to catch refcount transition
+* from 2 to 1:
 */
-   if (page_is_devmap_managed(>page)) {
-   put_devmap_managed_page(>page);
+   if (put_devmap_managed_page(>page))
return;
-   }
-
folio_put(folio);
 }
 
diff --git a/mm/memremap.c b/mm/memremap.c
index 55d23e9f5c04ec..f41233a67edb12 100644
--- a/mm/memremap.c
+++ b/mm/memremap.c
@@ -502,24 +502,22 @@ void free_devmap_managed_page(struct page *page)
page->pgmap->ops->page_free(page);
 }
 
-void put_devmap_managed_page(struct page *page)
+bool __put_devmap_managed_page(struct page *page)
 {
-   int count;
-
-   if (WARN_ON_ONCE(!page_is_devmap_managed(page)))
-   return;
-
-   count = page_ref_dec_return(page);
-
/*
 * devmap page refcounts are 1-based, rather than 0-based: if
 * refcount is 1, then the page is free and the refcount is
 * stable because nobody holds a reference on the page.
 */
-   if (count == 1)
+   switch (page_ref_dec_return(page)) {
+   case 1:
free_devmap_managed_page(page);
-   else if (!count)
+   break;
+   case 0:
__put_page(page);
+   break;
+   }
+   return true;
 }
-EXPORT_SYMBOL(put_devmap_managed_page);
+EXPORT_SYMBOL(__put_devmap_managed_page);
 #endif /* CONFIG_DEV_PAGEMAP_OPS */
diff --git a/mm/swap.c b/mm/swap.c
index 08058f74cae23e..25b55c56614311 100644
--- a/mm/swap.c
+++ b/mm/swap.c
@@ -930,16 +930,8 @@ void release_pages(struct page **pages, int nr)
unlock_page_lruvec_irqrestore(lruvec, flags);
lruvec = NULL;
}
-   /*
-* ZONE_DEVICE pages that return 'false' from
-* page_is_devmap_managed() do not require special
-* processing, and instead, expect a call to
-* put_page_testzero().
-*/
-   if (page_is_devmap_managed(page)) {
-   put_devmap_managed_page(page);
+   if (put_devmap_managed_page(page))
continue;
-   }
if (put_page_testzero(page))
put_dev_pagemap(page->pgmap);
continue;
-- 
2.30.2