diff mbox series

[1/2] ext4/xfs: add page refcount helper

Message ID 20200925204442.31348-2-rcampbell@nvidia.com (mailing list archive)
State New, archived
Headers show
Series mm: remove extra ZONE_DEVICE struct page refcount | expand

Commit Message

Ralph Campbell Sept. 25, 2020, 8:44 p.m. UTC
There are several places where ZONE_DEVICE struct pages assume a reference
count == 1 means the page is idle and free. Instead of open coding this,
add a helper function to hide this detail.

Signed-off-by: Ralph Campbell <rcampbell@nvidia.com>
---
 fs/dax.c            | 8 ++++----
 fs/ext4/inode.c     | 2 +-
 fs/xfs/xfs_file.c   | 2 +-
 include/linux/dax.h | 5 +++++
 4 files changed, 11 insertions(+), 6 deletions(-)

Comments

Dan Williams Sept. 25, 2020, 8:51 p.m. UTC | #1
On Fri, Sep 25, 2020 at 1:45 PM Ralph Campbell <rcampbell@nvidia.com> wrote:
>
> There are several places where ZONE_DEVICE struct pages assume a reference
> count == 1 means the page is idle and free. Instead of open coding this,
> add a helper function to hide this detail.
>
> Signed-off-by: Ralph Campbell <rcampbell@nvidia.com>
> ---
>  fs/dax.c            | 8 ++++----
>  fs/ext4/inode.c     | 2 +-
>  fs/xfs/xfs_file.c   | 2 +-
>  include/linux/dax.h | 5 +++++
>  4 files changed, 11 insertions(+), 6 deletions(-)
>
> diff --git a/fs/dax.c b/fs/dax.c
> index 994ab66a9907..8eddbcc0e149 100644
> --- a/fs/dax.c
> +++ b/fs/dax.c
> @@ -358,7 +358,7 @@ static void dax_disassociate_entry(void *entry, struct address_space *mapping,
>         for_each_mapped_pfn(entry, pfn) {
>                 struct page *page = pfn_to_page(pfn);
>
> -               WARN_ON_ONCE(trunc && page_ref_count(page) > 1);
> +               WARN_ON_ONCE(trunc && !dax_layout_is_idle_page(page));
>                 WARN_ON_ONCE(page->mapping && page->mapping != mapping);
>                 page->mapping = NULL;
>                 page->index = 0;
> @@ -372,7 +372,7 @@ static struct page *dax_busy_page(void *entry)
>         for_each_mapped_pfn(entry, pfn) {
>                 struct page *page = pfn_to_page(pfn);
>
> -               if (page_ref_count(page) > 1)
> +               if (!dax_layout_is_idle_page(page))
>                         return page;
>         }
>         return NULL;
> @@ -560,11 +560,11 @@ static void *grab_mapping_entry(struct xa_state *xas,
>
>  /**
>   * dax_layout_busy_page - find first pinned page in @mapping
> - * @mapping: address space to scan for a page with ref count > 1
> + * @mapping: address space to scan for a page with ref count > 0
>   *
>   * DAX requires ZONE_DEVICE mapped pages. These pages are never
>   * 'onlined' to the page allocator so they are considered idle when
> - * page->count == 1. A filesystem uses this interface to determine if
> + * page->count == 0. A filesystem uses this interface to determine if
>   * any page in the mapping is busy, i.e. for DMA, or other
>   * get_user_pages() usages.
>   *
> diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
> index bf596467c234..d9f8ad55523a 100644
> --- a/fs/ext4/inode.c
> +++ b/fs/ext4/inode.c
> @@ -3927,7 +3927,7 @@ int ext4_break_layouts(struct inode *inode)
>                         return 0;
>
>                 error = ___wait_var_event(&page->_refcount,
> -                               atomic_read(&page->_refcount) == 1,
> +                               dax_layout_is_idle_page(page),
>                                 TASK_INTERRUPTIBLE, 0, 0,
>                                 ext4_wait_dax_page(ei));
>         } while (error == 0);
> diff --git a/fs/xfs/xfs_file.c b/fs/xfs/xfs_file.c
> index a29f78a663ca..29ab96541bc1 100644
> --- a/fs/xfs/xfs_file.c
> +++ b/fs/xfs/xfs_file.c
> @@ -750,7 +750,7 @@ xfs_break_dax_layouts(
>
>         *retry = true;
>         return ___wait_var_event(&page->_refcount,
> -                       atomic_read(&page->_refcount) == 1, TASK_INTERRUPTIBLE,
> +                       dax_layout_is_idle_page(page), TASK_INTERRUPTIBLE,
>                         0, 0, xfs_wait_dax_page(inode));
>  }
>
> diff --git a/include/linux/dax.h b/include/linux/dax.h
> index 43b39ab9de1a..3f78ed78d1d6 100644
> --- a/include/linux/dax.h
> +++ b/include/linux/dax.h
> @@ -238,4 +238,9 @@ static inline bool dax_mapping(struct address_space *mapping)
>         return mapping->host && IS_DAX(mapping->host);
>  }
>
> +static inline bool dax_layout_is_idle_page(struct page *page)
> +{
> +       return page_ref_count(page) <= 1;

Why convert the check from "== 1" to "<= 1" and then back to the ==
operator in the next patch? A refcount < 1 in this path before your
other change is a bug.
Ralph Campbell Sept. 25, 2020, 9:17 p.m. UTC | #2
On 9/25/20 1:51 PM, Dan Williams wrote:
> On Fri, Sep 25, 2020 at 1:45 PM Ralph Campbell <rcampbell@nvidia.com> wrote:
>>
>> There are several places where ZONE_DEVICE struct pages assume a reference
>> count == 1 means the page is idle and free. Instead of open coding this,
>> add a helper function to hide this detail.
>>
>> Signed-off-by: Ralph Campbell <rcampbell@nvidia.com>
>> ---
>>   fs/dax.c            | 8 ++++----
>>   fs/ext4/inode.c     | 2 +-
>>   fs/xfs/xfs_file.c   | 2 +-
>>   include/linux/dax.h | 5 +++++
>>   4 files changed, 11 insertions(+), 6 deletions(-)
>>
>> diff --git a/fs/dax.c b/fs/dax.c
>> index 994ab66a9907..8eddbcc0e149 100644
>> --- a/fs/dax.c
>> +++ b/fs/dax.c
>> @@ -358,7 +358,7 @@ static void dax_disassociate_entry(void *entry, struct address_space *mapping,
>>          for_each_mapped_pfn(entry, pfn) {
>>                  struct page *page = pfn_to_page(pfn);
>>
>> -               WARN_ON_ONCE(trunc && page_ref_count(page) > 1);
>> +               WARN_ON_ONCE(trunc && !dax_layout_is_idle_page(page));
>>                  WARN_ON_ONCE(page->mapping && page->mapping != mapping);
>>                  page->mapping = NULL;
>>                  page->index = 0;
>> @@ -372,7 +372,7 @@ static struct page *dax_busy_page(void *entry)
>>          for_each_mapped_pfn(entry, pfn) {
>>                  struct page *page = pfn_to_page(pfn);
>>
>> -               if (page_ref_count(page) > 1)
>> +               if (!dax_layout_is_idle_page(page))
>>                          return page;
>>          }
>>          return NULL;
>> @@ -560,11 +560,11 @@ static void *grab_mapping_entry(struct xa_state *xas,
>>
>>   /**
>>    * dax_layout_busy_page - find first pinned page in @mapping
>> - * @mapping: address space to scan for a page with ref count > 1
>> + * @mapping: address space to scan for a page with ref count > 0
>>    *
>>    * DAX requires ZONE_DEVICE mapped pages. These pages are never
>>    * 'onlined' to the page allocator so they are considered idle when
>> - * page->count == 1. A filesystem uses this interface to determine if
>> + * page->count == 0. A filesystem uses this interface to determine if
>>    * any page in the mapping is busy, i.e. for DMA, or other
>>    * get_user_pages() usages.
>>    *
>> diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
>> index bf596467c234..d9f8ad55523a 100644
>> --- a/fs/ext4/inode.c
>> +++ b/fs/ext4/inode.c
>> @@ -3927,7 +3927,7 @@ int ext4_break_layouts(struct inode *inode)
>>                          return 0;
>>
>>                  error = ___wait_var_event(&page->_refcount,
>> -                               atomic_read(&page->_refcount) == 1,
>> +                               dax_layout_is_idle_page(page),
>>                                  TASK_INTERRUPTIBLE, 0, 0,
>>                                  ext4_wait_dax_page(ei));
>>          } while (error == 0);
>> diff --git a/fs/xfs/xfs_file.c b/fs/xfs/xfs_file.c
>> index a29f78a663ca..29ab96541bc1 100644
>> --- a/fs/xfs/xfs_file.c
>> +++ b/fs/xfs/xfs_file.c
>> @@ -750,7 +750,7 @@ xfs_break_dax_layouts(
>>
>>          *retry = true;
>>          return ___wait_var_event(&page->_refcount,
>> -                       atomic_read(&page->_refcount) == 1, TASK_INTERRUPTIBLE,
>> +                       dax_layout_is_idle_page(page), TASK_INTERRUPTIBLE,
>>                          0, 0, xfs_wait_dax_page(inode));
>>   }
>>
>> diff --git a/include/linux/dax.h b/include/linux/dax.h
>> index 43b39ab9de1a..3f78ed78d1d6 100644
>> --- a/include/linux/dax.h
>> +++ b/include/linux/dax.h
>> @@ -238,4 +238,9 @@ static inline bool dax_mapping(struct address_space *mapping)
>>          return mapping->host && IS_DAX(mapping->host);
>>   }
>>
>> +static inline bool dax_layout_is_idle_page(struct page *page)
>> +{
>> +       return page_ref_count(page) <= 1;
> 
> Why convert the check from "== 1" to "<= 1" and then back to the ==
> operator in the next patch? A refcount < 1 in this path before your
> other change is a bug.
> 
Mostly I was thinking > 1 was busy so <= 1 is idle. And yes, <=0 is never
supposed to happen. Checking for == 1 is probably better though.
Christoph Hellwig Sept. 26, 2020, 6:35 a.m. UTC | #3
On Fri, Sep 25, 2020 at 01:44:41PM -0700, Ralph Campbell wrote:
>  		error = ___wait_var_event(&page->_refcount,
> -				atomic_read(&page->_refcount) == 1,
> +				dax_layout_is_idle_page(page),
>  				TASK_INTERRUPTIBLE, 0, 0,
>  				ext4_wait_dax_page(ei));

> +++ b/fs/xfs/xfs_file.c
> @@ -750,7 +750,7 @@ xfs_break_dax_layouts(
>  
>  	*retry = true;
>  	return ___wait_var_event(&page->_refcount,
> -			atomic_read(&page->_refcount) == 1, TASK_INTERRUPTIBLE,
> +			dax_layout_is_idle_page(page), TASK_INTERRUPTIBLE,
>  			0, 0, xfs_wait_dax_page(inode));
>  }

I still think a litte helper macro would be nice here:

#define dax_wait_page(_inode, _page, _wait_cb)				\
  	___wait_var_event(&(_page)->_refcount,				\
		atomic_read(&(_page)->_refcount) == 1,			\
		TASK_INTERRUPTIBLE, dax_layout_is_idle_page(_page),	\
		TASK_INTERRUPTIBLE, 0, 0, _wait_cb(_inode));
Ralph Campbell Sept. 28, 2020, 10:20 p.m. UTC | #4
On 9/25/20 11:35 PM, Christoph Hellwig wrote:
> On Fri, Sep 25, 2020 at 01:44:41PM -0700, Ralph Campbell wrote:
>>   		error = ___wait_var_event(&page->_refcount,
>> -				atomic_read(&page->_refcount) == 1,
>> +				dax_layout_is_idle_page(page),
>>   				TASK_INTERRUPTIBLE, 0, 0,
>>   				ext4_wait_dax_page(ei));
> 
>> +++ b/fs/xfs/xfs_file.c
>> @@ -750,7 +750,7 @@ xfs_break_dax_layouts(
>>   
>>   	*retry = true;
>>   	return ___wait_var_event(&page->_refcount,
>> -			atomic_read(&page->_refcount) == 1, TASK_INTERRUPTIBLE,
>> +			dax_layout_is_idle_page(page), TASK_INTERRUPTIBLE,
>>   			0, 0, xfs_wait_dax_page(inode));
>>   }
> 
> I still think a litte helper macro would be nice here:
> 
> #define dax_wait_page(_inode, _page, _wait_cb)				\
>    	___wait_var_event(&(_page)->_refcount,				\
> 		atomic_read(&(_page)->_refcount) == 1,			\
> 		TASK_INTERRUPTIBLE, dax_layout_is_idle_page(_page),	\
> 		TASK_INTERRUPTIBLE, 0, 0, _wait_cb(_inode));

OK, I'll add it in v3.
diff mbox series

Patch

diff --git a/fs/dax.c b/fs/dax.c
index 994ab66a9907..8eddbcc0e149 100644
--- a/fs/dax.c
+++ b/fs/dax.c
@@ -358,7 +358,7 @@  static void dax_disassociate_entry(void *entry, struct address_space *mapping,
 	for_each_mapped_pfn(entry, pfn) {
 		struct page *page = pfn_to_page(pfn);
 
-		WARN_ON_ONCE(trunc && page_ref_count(page) > 1);
+		WARN_ON_ONCE(trunc && !dax_layout_is_idle_page(page));
 		WARN_ON_ONCE(page->mapping && page->mapping != mapping);
 		page->mapping = NULL;
 		page->index = 0;
@@ -372,7 +372,7 @@  static struct page *dax_busy_page(void *entry)
 	for_each_mapped_pfn(entry, pfn) {
 		struct page *page = pfn_to_page(pfn);
 
-		if (page_ref_count(page) > 1)
+		if (!dax_layout_is_idle_page(page))
 			return page;
 	}
 	return NULL;
@@ -560,11 +560,11 @@  static void *grab_mapping_entry(struct xa_state *xas,
 
 /**
  * dax_layout_busy_page - find first pinned page in @mapping
- * @mapping: address space to scan for a page with ref count > 1
+ * @mapping: address space to scan for a page with ref count > 0
  *
  * DAX requires ZONE_DEVICE mapped pages. These pages are never
  * 'onlined' to the page allocator so they are considered idle when
- * page->count == 1. A filesystem uses this interface to determine if
+ * page->count == 0. A filesystem uses this interface to determine if
  * any page in the mapping is busy, i.e. for DMA, or other
  * get_user_pages() usages.
  *
diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
index bf596467c234..d9f8ad55523a 100644
--- a/fs/ext4/inode.c
+++ b/fs/ext4/inode.c
@@ -3927,7 +3927,7 @@  int ext4_break_layouts(struct inode *inode)
 			return 0;
 
 		error = ___wait_var_event(&page->_refcount,
-				atomic_read(&page->_refcount) == 1,
+				dax_layout_is_idle_page(page),
 				TASK_INTERRUPTIBLE, 0, 0,
 				ext4_wait_dax_page(ei));
 	} while (error == 0);
diff --git a/fs/xfs/xfs_file.c b/fs/xfs/xfs_file.c
index a29f78a663ca..29ab96541bc1 100644
--- a/fs/xfs/xfs_file.c
+++ b/fs/xfs/xfs_file.c
@@ -750,7 +750,7 @@  xfs_break_dax_layouts(
 
 	*retry = true;
 	return ___wait_var_event(&page->_refcount,
-			atomic_read(&page->_refcount) == 1, TASK_INTERRUPTIBLE,
+			dax_layout_is_idle_page(page), TASK_INTERRUPTIBLE,
 			0, 0, xfs_wait_dax_page(inode));
 }
 
diff --git a/include/linux/dax.h b/include/linux/dax.h
index 43b39ab9de1a..3f78ed78d1d6 100644
--- a/include/linux/dax.h
+++ b/include/linux/dax.h
@@ -238,4 +238,9 @@  static inline bool dax_mapping(struct address_space *mapping)
 	return mapping->host && IS_DAX(mapping->host);
 }
 
+static inline bool dax_layout_is_idle_page(struct page *page)
+{
+	return page_ref_count(page) <= 1;
+}
+
 #endif