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[PATCH 1/5] mm/debug_pagealloc: clean-up guard page handling code

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  [PATCH 1/5] mm/debug_pagealloc: clean-up guard page handling code js1304@gmail.com - 2016-08-10 21:20 +0200
    Re: [PATCH 1/5] mm/debug_pagealloc: clean-up guard page handling code Sergey Senozhatsky <sergey.senozhatsky@gmail.com> - 2016-08-10 23:10 +0200
      Re: [PATCH 1/5] mm/debug_pagealloc: clean-up guard page handling code Vlastimil Babka <vbabka@suse.cz> - 2016-08-11 11:50 +0200
        Re: [PATCH 1/5] mm/debug_pagealloc: clean-up guard page handling code Sergey Senozhatsky <sergey.senozhatsky@gmail.com> - 2016-08-12 14:30 +0200
          Re: [PATCH 1/5] mm/debug_pagealloc: clean-up guard page handling code Joonsoo Kim <iamjoonsoo.kim@lge.com> - 2016-08-16 05:00 +0200
    Re: [PATCH 1/5] mm/debug_pagealloc: clean-up guard page handling code Vlastimil Babka <vbabka@suse.cz> - 2016-08-11 11:40 +0200

#1459629 — [PATCH 1/5] mm/debug_pagealloc: clean-up guard page handling code

From: Joonsoo Kim <iamjoonsoo.kim@lge.com>

We can make code clean by moving decision condition
for set_page_guard() into set_page_guard() itself. It will
help code readability. There is no functional change.

Signed-off-by: Joonsoo Kim <iamjoonsoo.kim@lge.com>
---
 mm/page_alloc.c | 34 ++++++++++++++++++----------------
 1 file changed, 18 insertions(+), 16 deletions(-)

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 277c3d0..5e7944b 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -638,17 +638,20 @@ static int __init debug_guardpage_minorder_setup(char *buf)
 }
 __setup("debug_guardpage_minorder=", debug_guardpage_minorder_setup);
 
-static inline void set_page_guard(struct zone *zone, struct page *page,
+static inline bool set_page_guard(struct zone *zone, struct page *page,
 				unsigned int order, int migratetype)
 {
 	struct page_ext *page_ext;
 
 	if (!debug_guardpage_enabled())
-		return;
+		return false;
+
+	if (order >= debug_guardpage_minorder())
+		return false;
 
 	page_ext = lookup_page_ext(page);
 	if (unlikely(!page_ext))
-		return;
+		return false;
 
 	__set_bit(PAGE_EXT_DEBUG_GUARD, &page_ext->flags);
 
@@ -656,6 +659,8 @@ static inline void set_page_guard(struct zone *zone, struct page *page,
 	set_page_private(page, order);
 	/* Guard pages are not available for any usage */
 	__mod_zone_freepage_state(zone, -(1 << order), migratetype);
+
+	return true;
 }
 
 static inline void clear_page_guard(struct zone *zone, struct page *page,
@@ -678,8 +683,8 @@ static inline void clear_page_guard(struct zone *zone, struct page *page,
 }
 #else
 struct page_ext_operations debug_guardpage_ops = { NULL, };
-static inline void set_page_guard(struct zone *zone, struct page *page,
-				unsigned int order, int migratetype) {}
+static inline bool set_page_guard(struct zone *zone, struct page *page,
+			unsigned int order, int migratetype) { return false; }
 static inline void clear_page_guard(struct zone *zone, struct page *page,
 				unsigned int order, int migratetype) {}
 #endif
@@ -1650,18 +1655,15 @@ static inline void expand(struct zone *zone, struct page *page,
 		size >>= 1;
 		VM_BUG_ON_PAGE(bad_range(zone, &page[size]), &page[size]);
 
-		if (IS_ENABLED(CONFIG_DEBUG_PAGEALLOC) &&
-			debug_guardpage_enabled() &&
-			high < debug_guardpage_minorder()) {
-			/*
-			 * Mark as guard pages (or page), that will allow to
-			 * merge back to allocator when buddy will be freed.
-			 * Corresponding page table entries will not be touched,
-			 * pages will stay not present in virtual address space
-			 */
-			set_page_guard(zone, &page[size], high, migratetype);
+		/*
+		 * Mark as guard pages (or page), that will allow to
+		 * merge back to allocator when buddy will be freed.
+		 * Corresponding page table entries will not be touched,
+		 * pages will stay not present in virtual address space
+		 */
+		if (set_page_guard(zone, &page[size], high, migratetype))
 			continue;
-		}
+
 		list_add(&page[size].lru, &area->free_list[migratetype]);
 		area->nr_free++;
 		set_page_order(&page[size], high);
-- 
1.9.1

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#1459940

Hello,

On (08/10/16 15:16), js1304@gmail.com wrote:
[..]
> -static inline void set_page_guard(struct zone *zone, struct page *page,
> +static inline bool set_page_guard(struct zone *zone, struct page *page,
>  				unsigned int order, int migratetype)
>  {
>  	struct page_ext *page_ext;
>  
>  	if (!debug_guardpage_enabled())
> -		return;
> +		return false;
> +
> +	if (order >= debug_guardpage_minorder())
> +		return false;
>  
>  	page_ext = lookup_page_ext(page);
>  	if (unlikely(!page_ext))
> -		return;
> +		return false;
>  
>  	__set_bit(PAGE_EXT_DEBUG_GUARD, &page_ext->flags);
>  
> @@ -656,6 +659,8 @@ static inline void set_page_guard(struct zone *zone, struct page *page,
>  	set_page_private(page, order);
>  	/* Guard pages are not available for any usage */
>  	__mod_zone_freepage_state(zone, -(1 << order), migratetype);
> +
> +	return true;
>  }
>  
>  static inline void clear_page_guard(struct zone *zone, struct page *page,
> @@ -678,8 +683,8 @@ static inline void clear_page_guard(struct zone *zone, struct page *page,
>  }
>  #else
>  struct page_ext_operations debug_guardpage_ops = { NULL, };
> -static inline void set_page_guard(struct zone *zone, struct page *page,
> -				unsigned int order, int migratetype) {}
> +static inline bool set_page_guard(struct zone *zone, struct page *page,
> +			unsigned int order, int migratetype) { return false; }
>  static inline void clear_page_guard(struct zone *zone, struct page *page,
>  				unsigned int order, int migratetype) {}
>  #endif
> @@ -1650,18 +1655,15 @@ static inline void expand(struct zone *zone, struct page *page,
>  		size >>= 1;
>  		VM_BUG_ON_PAGE(bad_range(zone, &page[size]), &page[size]);
>  
> -		if (IS_ENABLED(CONFIG_DEBUG_PAGEALLOC) &&
> -			debug_guardpage_enabled() &&
> -			high < debug_guardpage_minorder()) {
> -			/*
> -			 * Mark as guard pages (or page), that will allow to
> -			 * merge back to allocator when buddy will be freed.
> -			 * Corresponding page table entries will not be touched,
> -			 * pages will stay not present in virtual address space
> -			 */
> -			set_page_guard(zone, &page[size], high, migratetype);
> +		/*
> +		 * Mark as guard pages (or page), that will allow to
> +		 * merge back to allocator when buddy will be freed.
> +		 * Corresponding page table entries will not be touched,
> +		 * pages will stay not present in virtual address space
> +		 */
> +		if (set_page_guard(zone, &page[size], high, migratetype))
>  			continue;
> -		}

so previously IS_ENABLED(CONFIG_DEBUG_PAGEALLOC) could have optimized out
the entire branch -- no set_page_guard() invocation and checks, right? but
now we would call set_page_guard() every time?

	-ss

> +
>  		list_add(&page[size].lru, &area->free_list[migratetype]);
>  		area->nr_free++;
>  		set_page_order(&page[size], high);

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#1460344

On 08/10/2016 10:14 AM, Sergey Senozhatsky wrote:
>> @@ -1650,18 +1655,15 @@ static inline void expand(struct zone *zone, struct page *page,
>>  		size >>= 1;
>>  		VM_BUG_ON_PAGE(bad_range(zone, &page[size]), &page[size]);
>>
>> -		if (IS_ENABLED(CONFIG_DEBUG_PAGEALLOC) &&
>> -			debug_guardpage_enabled() &&
>> -			high < debug_guardpage_minorder()) {
>> -			/*
>> -			 * Mark as guard pages (or page), that will allow to
>> -			 * merge back to allocator when buddy will be freed.
>> -			 * Corresponding page table entries will not be touched,
>> -			 * pages will stay not present in virtual address space
>> -			 */
>> -			set_page_guard(zone, &page[size], high, migratetype);
>> +		/*
>> +		 * Mark as guard pages (or page), that will allow to
>> +		 * merge back to allocator when buddy will be freed.
>> +		 * Corresponding page table entries will not be touched,
>> +		 * pages will stay not present in virtual address space
>> +		 */
>> +		if (set_page_guard(zone, &page[size], high, migratetype))
>>  			continue;
>> -		}
>
> so previously IS_ENABLED(CONFIG_DEBUG_PAGEALLOC) could have optimized out
> the entire branch -- no set_page_guard() invocation and checks, right? but
> now we would call set_page_guard() every time?

No, there's a !CONFIG_DEBUG_PAGEALLOC version of set_page_guard() that 
returns false (static inline), so this whole if will be eliminated by 
the compiler, same as before.

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#1461141

On (08/11/16 11:41), Vlastimil Babka wrote:
> On 08/10/2016 10:14 AM, Sergey Senozhatsky wrote:
> > > @@ -1650,18 +1655,15 @@ static inline void expand(struct zone *zone, struct page *page,
> > >  		size >>= 1;
> > >  		VM_BUG_ON_PAGE(bad_range(zone, &page[size]), &page[size]);
> > > 
> > > -		if (IS_ENABLED(CONFIG_DEBUG_PAGEALLOC) &&
> > > -			debug_guardpage_enabled() &&
> > > -			high < debug_guardpage_minorder()) {
> > > -			/*
> > > -			 * Mark as guard pages (or page), that will allow to
> > > -			 * merge back to allocator when buddy will be freed.
> > > -			 * Corresponding page table entries will not be touched,
> > > -			 * pages will stay not present in virtual address space
> > > -			 */
> > > -			set_page_guard(zone, &page[size], high, migratetype);
> > > +		/*
> > > +		 * Mark as guard pages (or page), that will allow to
> > > +		 * merge back to allocator when buddy will be freed.
> > > +		 * Corresponding page table entries will not be touched,
> > > +		 * pages will stay not present in virtual address space
> > > +		 */
> > > +		if (set_page_guard(zone, &page[size], high, migratetype))
> > >  			continue;
> > > -		}
> > 
> > so previously IS_ENABLED(CONFIG_DEBUG_PAGEALLOC) could have optimized out
> > the entire branch -- no set_page_guard() invocation and checks, right? but
> > now we would call set_page_guard() every time?
> 
> No, there's a !CONFIG_DEBUG_PAGEALLOC version of set_page_guard() that
> returns false (static inline), so this whole if will be eliminated by the
> compiler, same as before.

ah, indeed. didn't notice it.

	-ss

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#1463361

On Fri, Aug 12, 2016 at 09:25:37PM +0900, Sergey Senozhatsky wrote:
> On (08/11/16 11:41), Vlastimil Babka wrote:
> > On 08/10/2016 10:14 AM, Sergey Senozhatsky wrote:
> > > > @@ -1650,18 +1655,15 @@ static inline void expand(struct zone *zone, struct page *page,
> > > >  		size >>= 1;
> > > >  		VM_BUG_ON_PAGE(bad_range(zone, &page[size]), &page[size]);
> > > > 
> > > > -		if (IS_ENABLED(CONFIG_DEBUG_PAGEALLOC) &&
> > > > -			debug_guardpage_enabled() &&
> > > > -			high < debug_guardpage_minorder()) {
> > > > -			/*
> > > > -			 * Mark as guard pages (or page), that will allow to
> > > > -			 * merge back to allocator when buddy will be freed.
> > > > -			 * Corresponding page table entries will not be touched,
> > > > -			 * pages will stay not present in virtual address space
> > > > -			 */
> > > > -			set_page_guard(zone, &page[size], high, migratetype);
> > > > +		/*
> > > > +		 * Mark as guard pages (or page), that will allow to
> > > > +		 * merge back to allocator when buddy will be freed.
> > > > +		 * Corresponding page table entries will not be touched,
> > > > +		 * pages will stay not present in virtual address space
> > > > +		 */
> > > > +		if (set_page_guard(zone, &page[size], high, migratetype))
> > > >  			continue;
> > > > -		}
> > > 
> > > so previously IS_ENABLED(CONFIG_DEBUG_PAGEALLOC) could have optimized out
> > > the entire branch -- no set_page_guard() invocation and checks, right? but
> > > now we would call set_page_guard() every time?
> > 
> > No, there's a !CONFIG_DEBUG_PAGEALLOC version of set_page_guard() that
> > returns false (static inline), so this whole if will be eliminated by the
> > compiler, same as before.
> 
> ah, indeed. didn't notice it.

Hello, Sergey and Vlastimil.

I fixed all you commented and sent v2.

Thanks.

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#1460324

On 08/10/2016 08:16 AM, js1304@gmail.com wrote:
> From: Joonsoo Kim <iamjoonsoo.kim@lge.com>
>
> We can make code clean by moving decision condition
> for set_page_guard() into set_page_guard() itself. It will
> help code readability. There is no functional change.
>
> Signed-off-by: Joonsoo Kim <iamjoonsoo.kim@lge.com>

Acked-by: Vlastimil Babka <vbabka@suse.cz>

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