[1/4] mm/page_alloc.c: extract commom part to check page
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Message ID 20200119131408.23247-2-richardw.yang@linux.intel.com
State New
Headers show
Series
  • mm/page_alloc.c: cleanup on check page
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Commit Message

Wei Yang Jan. 19, 2020, 1:14 p.m. UTC
During free and new page, we did some check on the status of page
struct.

There is some common part, just extract them.

Signed-off-by: Wei Yang <richardw.yang@linux.intel.com>
---
 mm/page_alloc.c | 36 ++++++++++++++++--------------------
 1 file changed, 16 insertions(+), 20 deletions(-)

Comments

David Rientjes Jan. 19, 2020, 10:06 p.m. UTC | #1
On Sun, 19 Jan 2020, Wei Yang wrote:

> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index d047bf7d8fd4..8cd06729169f 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -1025,13 +1025,9 @@ static inline bool page_expected_state(struct page *page,
>  	return true;
>  }
>  
> -static void free_pages_check_bad(struct page *page)
> +static inline const char *__check_page(struct page *page)
>  {
> -	const char *bad_reason;
> -	unsigned long bad_flags;
> -
> -	bad_reason = NULL;
> -	bad_flags = 0;
> +	const char *bad_reason = NULL;
>  
>  	if (unlikely(atomic_read(&page->_mapcount) != -1))
>  		bad_reason = "nonzero mapcount";
> @@ -1039,14 +1035,23 @@ static void free_pages_check_bad(struct page *page)
>  		bad_reason = "non-NULL mapping";
>  	if (unlikely(page_ref_count(page) != 0))
>  		bad_reason = "nonzero _refcount";
> -	if (unlikely(page->flags & PAGE_FLAGS_CHECK_AT_FREE)) {
> -		bad_reason = "PAGE_FLAGS_CHECK_AT_FREE flag(s) set";
> -		bad_flags = PAGE_FLAGS_CHECK_AT_FREE;
> -	}
>  #ifdef CONFIG_MEMCG
>  	if (unlikely(page->mem_cgroup))
>  		bad_reason = "page still charged to cgroup";
>  #endif
> +	return bad_reason;
> +}
> +
> +static void free_pages_check_bad(struct page *page)
> +{
> +	const char *bad_reason = NULL;
> +	unsigned long bad_flags = 0;
> +
> +	bad_reason = __check_page(page);
> +	if (unlikely(page->flags & PAGE_FLAGS_CHECK_AT_FREE)) {
> +		bad_reason = "PAGE_FLAGS_CHECK_AT_FREE flag(s) set";
> +		bad_flags = PAGE_FLAGS_CHECK_AT_FREE;
> +	}
>  	bad_page(page, bad_reason, bad_flags);
>  }
>  
> @@ -2044,12 +2049,7 @@ static void check_new_page_bad(struct page *page)
>  	const char *bad_reason = NULL;
>  	unsigned long bad_flags = 0;
>  
> -	if (unlikely(atomic_read(&page->_mapcount) != -1))
> -		bad_reason = "nonzero mapcount";
> -	if (unlikely(page->mapping != NULL))
> -		bad_reason = "non-NULL mapping";
> -	if (unlikely(page_ref_count(page) != 0))
> -		bad_reason = "nonzero _refcount";
> +	bad_reason = __check_page(page);
>  	if (unlikely(page->flags & __PG_HWPOISON)) {
>  		bad_reason = "HWPoisoned (hardware-corrupted)";
>  		bad_flags = __PG_HWPOISON;
> @@ -2061,10 +2061,6 @@ static void check_new_page_bad(struct page *page)
>  		bad_reason = "PAGE_FLAGS_CHECK_AT_PREP flag set";
>  		bad_flags = PAGE_FLAGS_CHECK_AT_PREP;
>  	}
> -#ifdef CONFIG_MEMCG
> -	if (unlikely(page->mem_cgroup))
> -		bad_reason = "page still charged to cgroup";
> -#endif
>  	bad_page(page, bad_reason, bad_flags);
>  }
>  

I think this is compounding a previous problem in these functions: these 
are all "if" clauses, not "else if" clauses so they are presumably ordered 
based on least significant to most significant (we only see the last 
bad_reason that we find).  For the page->mem_cgroup check, this leaves 
bad_flags set but it doesn't match bad_reason.

Could you instead fix the problem with these functions so that we actually 
list *all* the problems with the page rather than only the last 
conditional that is true?
Wei Yang Jan. 20, 2020, 12:33 a.m. UTC | #2
On Sun, Jan 19, 2020 at 02:06:18PM -0800, David Rientjes wrote:
>On Sun, 19 Jan 2020, Wei Yang wrote:
>
>> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
>> index d047bf7d8fd4..8cd06729169f 100644
>> --- a/mm/page_alloc.c
>> +++ b/mm/page_alloc.c
>> @@ -1025,13 +1025,9 @@ static inline bool page_expected_state(struct page *page,
>>  	return true;
>>  }
>>  
>> -static void free_pages_check_bad(struct page *page)
>> +static inline const char *__check_page(struct page *page)
>>  {
>> -	const char *bad_reason;
>> -	unsigned long bad_flags;
>> -
>> -	bad_reason = NULL;
>> -	bad_flags = 0;
>> +	const char *bad_reason = NULL;
>>  
>>  	if (unlikely(atomic_read(&page->_mapcount) != -1))
>>  		bad_reason = "nonzero mapcount";
>> @@ -1039,14 +1035,23 @@ static void free_pages_check_bad(struct page *page)
>>  		bad_reason = "non-NULL mapping";
>>  	if (unlikely(page_ref_count(page) != 0))
>>  		bad_reason = "nonzero _refcount";
>> -	if (unlikely(page->flags & PAGE_FLAGS_CHECK_AT_FREE)) {
>> -		bad_reason = "PAGE_FLAGS_CHECK_AT_FREE flag(s) set";
>> -		bad_flags = PAGE_FLAGS_CHECK_AT_FREE;
>> -	}
>>  #ifdef CONFIG_MEMCG
>>  	if (unlikely(page->mem_cgroup))
>>  		bad_reason = "page still charged to cgroup";
>>  #endif
>> +	return bad_reason;
>> +}
>> +
>> +static void free_pages_check_bad(struct page *page)
>> +{
>> +	const char *bad_reason = NULL;
>> +	unsigned long bad_flags = 0;
>> +
>> +	bad_reason = __check_page(page);
>> +	if (unlikely(page->flags & PAGE_FLAGS_CHECK_AT_FREE)) {
>> +		bad_reason = "PAGE_FLAGS_CHECK_AT_FREE flag(s) set";
>> +		bad_flags = PAGE_FLAGS_CHECK_AT_FREE;
>> +	}
>>  	bad_page(page, bad_reason, bad_flags);
>>  }
>>  
>> @@ -2044,12 +2049,7 @@ static void check_new_page_bad(struct page *page)
>>  	const char *bad_reason = NULL;
>>  	unsigned long bad_flags = 0;
>>  
>> -	if (unlikely(atomic_read(&page->_mapcount) != -1))
>> -		bad_reason = "nonzero mapcount";
>> -	if (unlikely(page->mapping != NULL))
>> -		bad_reason = "non-NULL mapping";
>> -	if (unlikely(page_ref_count(page) != 0))
>> -		bad_reason = "nonzero _refcount";
>> +	bad_reason = __check_page(page);
>>  	if (unlikely(page->flags & __PG_HWPOISON)) {
>>  		bad_reason = "HWPoisoned (hardware-corrupted)";
>>  		bad_flags = __PG_HWPOISON;
>> @@ -2061,10 +2061,6 @@ static void check_new_page_bad(struct page *page)
>>  		bad_reason = "PAGE_FLAGS_CHECK_AT_PREP flag set";
>>  		bad_flags = PAGE_FLAGS_CHECK_AT_PREP;
>>  	}
>> -#ifdef CONFIG_MEMCG
>> -	if (unlikely(page->mem_cgroup))
>> -		bad_reason = "page still charged to cgroup";
>> -#endif
>>  	bad_page(page, bad_reason, bad_flags);
>>  }
>>  
>
>I think this is compounding a previous problem in these functions: these 
>are all "if" clauses, not "else if" clauses so they are presumably ordered 
>based on least significant to most significant (we only see the last 
>bad_reason that we find).  For the page->mem_cgroup check, this leaves 
>bad_flags set but it doesn't match bad_reason.
>

I have thought about this. And curious about the order of those reasons.

>Could you instead fix the problem with these functions so that we actually 
>list *all* the problems with the page rather than only the last 
>conditional that is true?

Sure, thanks for the suggestion.

Patch
diff mbox series

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index d047bf7d8fd4..8cd06729169f 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -1025,13 +1025,9 @@  static inline bool page_expected_state(struct page *page,
 	return true;
 }
 
-static void free_pages_check_bad(struct page *page)
+static inline const char *__check_page(struct page *page)
 {
-	const char *bad_reason;
-	unsigned long bad_flags;
-
-	bad_reason = NULL;
-	bad_flags = 0;
+	const char *bad_reason = NULL;
 
 	if (unlikely(atomic_read(&page->_mapcount) != -1))
 		bad_reason = "nonzero mapcount";
@@ -1039,14 +1035,23 @@  static void free_pages_check_bad(struct page *page)
 		bad_reason = "non-NULL mapping";
 	if (unlikely(page_ref_count(page) != 0))
 		bad_reason = "nonzero _refcount";
-	if (unlikely(page->flags & PAGE_FLAGS_CHECK_AT_FREE)) {
-		bad_reason = "PAGE_FLAGS_CHECK_AT_FREE flag(s) set";
-		bad_flags = PAGE_FLAGS_CHECK_AT_FREE;
-	}
 #ifdef CONFIG_MEMCG
 	if (unlikely(page->mem_cgroup))
 		bad_reason = "page still charged to cgroup";
 #endif
+	return bad_reason;
+}
+
+static void free_pages_check_bad(struct page *page)
+{
+	const char *bad_reason = NULL;
+	unsigned long bad_flags = 0;
+
+	bad_reason = __check_page(page);
+	if (unlikely(page->flags & PAGE_FLAGS_CHECK_AT_FREE)) {
+		bad_reason = "PAGE_FLAGS_CHECK_AT_FREE flag(s) set";
+		bad_flags = PAGE_FLAGS_CHECK_AT_FREE;
+	}
 	bad_page(page, bad_reason, bad_flags);
 }
 
@@ -2044,12 +2049,7 @@  static void check_new_page_bad(struct page *page)
 	const char *bad_reason = NULL;
 	unsigned long bad_flags = 0;
 
-	if (unlikely(atomic_read(&page->_mapcount) != -1))
-		bad_reason = "nonzero mapcount";
-	if (unlikely(page->mapping != NULL))
-		bad_reason = "non-NULL mapping";
-	if (unlikely(page_ref_count(page) != 0))
-		bad_reason = "nonzero _refcount";
+	bad_reason = __check_page(page);
 	if (unlikely(page->flags & __PG_HWPOISON)) {
 		bad_reason = "HWPoisoned (hardware-corrupted)";
 		bad_flags = __PG_HWPOISON;
@@ -2061,10 +2061,6 @@  static void check_new_page_bad(struct page *page)
 		bad_reason = "PAGE_FLAGS_CHECK_AT_PREP flag set";
 		bad_flags = PAGE_FLAGS_CHECK_AT_PREP;
 	}
-#ifdef CONFIG_MEMCG
-	if (unlikely(page->mem_cgroup))
-		bad_reason = "page still charged to cgroup";
-#endif
 	bad_page(page, bad_reason, bad_flags);
 }