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* [PATCH 0/1] mm/page_ext: remove unnecessary stack_trace field
@ 2015-01-26 21:52 Sergei Rogachev
  2015-01-26 21:52 ` [PATCH 1/1] " Sergei Rogachev
  0 siblings, 1 reply; 5+ messages in thread
From: Sergei Rogachev @ 2015-01-26 21:52 UTC (permalink / raw)
  To: akpm, iamjoonsoo.kim; +Cc: LKML, Sergei Rogachev

The functionality named "page owner" has resurrected the structure page_ext
which is used for keeping additional page-related information. Every page in
the system has its own corresponding page_ext structure.

Page owner uses this structure to keep allocation order, gfp_mask and backtrace
entries; moreover page_ext includes a field of type "struct stack_trace". And
this field is used for collecting backtraces: a pointer to struct stack_trace is
passed to save_stack_trace in the function __set_page_owner. But it is really
not necessary to keep dedicated stack_trace structures for all physical pages in
the system, only an amount of saved backtrace entries is needed to be saved.

The stack_trace structure can be allocated on the stack (it is relatively small)
and used for save_stack_trace invocation. Such change can save 12 bytes of
memory per page if page owner functionality is enabled.

Sergei Rogachev (1):
  mm/page_ext: remove unnecessary stack_trace field

 include/linux/page_ext.h |  2 +-
 mm/page_owner.c          | 21 ++++++++++++---------
 2 files changed, 13 insertions(+), 10 deletions(-)

-- 
1.9.1


^ permalink raw reply	[flat|nested] 5+ messages in thread
* [PATCH 1/1] mm/page_ext: remove unnecessary stack_trace field
  2015-01-26 21:52 [PATCH 0/1] mm/page_ext: remove unnecessary stack_trace field Sergei Rogachev
@ 2015-01-26 21:52 ` Sergei Rogachev
  2015-01-27  8:36   ` Joonsoo Kim
  2015-01-27 22:43   ` Andrew Morton
  0 siblings, 2 replies; 5+ messages in thread
From: Sergei Rogachev @ 2015-01-26 21:52 UTC (permalink / raw)
  To: akpm, iamjoonsoo.kim; +Cc: LKML, Sergei Rogachev

Page owner uses the page_ext structure to keep meta-information
for every page in the system. The structure also contains a field
of type 'struct stack_trace', page owner uses this field during
invocation of the function save_stack_trace. It is easy to notice
that keeping a copy of this structure for every page in the system
is very inefficiently in terms of memory.

The patch removes this unnecessary field of page_ext and forces
page owner to use a stack_trace structure allocated on the stack.

Signed-off-by: Sergei Rogachev <rogachevsergei@gmail.com>
---
 include/linux/page_ext.h |  2 +-
 mm/page_owner.c          | 21 ++++++++++++---------
 2 files changed, 13 insertions(+), 10 deletions(-)

diff --git a/include/linux/page_ext.h b/include/linux/page_ext.h
index d2a2c84..c42981c 100644
--- a/include/linux/page_ext.h
+++ b/include/linux/page_ext.h
@@ -40,7 +40,7 @@ struct page_ext {
 #ifdef CONFIG_PAGE_OWNER
 	unsigned int order;
 	gfp_t gfp_mask;
-	struct stack_trace trace;
+	unsigned int nr_entries;
 	unsigned long trace_entries[8];
 #endif
 };
diff --git a/mm/page_owner.c b/mm/page_owner.c
index 9ab4a9b..f7f3318 100644
--- a/mm/page_owner.c
+++ b/mm/page_owner.c
@@ -60,19 +60,19 @@ void __reset_page_owner(struct page *page, unsigned int order)
 void __set_page_owner(struct page *page, unsigned int order, gfp_t gfp_mask)
 {
 	struct page_ext *page_ext;
-	struct stack_trace *trace;
+	struct stack_trace trace;
 
 	page_ext = lookup_page_ext(page);
 
-	trace = &page_ext->trace;
-	trace->nr_entries = 0;
-	trace->max_entries = ARRAY_SIZE(page_ext->trace_entries);
-	trace->entries = &page_ext->trace_entries[0];
-	trace->skip = 3;
-	save_stack_trace(&page_ext->trace);
+	trace.nr_entries = 0;
+	trace.max_entries = ARRAY_SIZE(page_ext->trace_entries);
+	trace.entries = &page_ext->trace_entries[0];
+	trace.skip = 3;
+	save_stack_trace(&trace);
 
 	page_ext->order = order;
 	page_ext->gfp_mask = gfp_mask;
+	page_ext->nr_entries = trace.nr_entries;
 
 	__set_bit(PAGE_EXT_OWNER, &page_ext->flags);
 }
@@ -83,6 +83,7 @@ print_page_owner(char __user *buf, size_t count, unsigned long pfn,
 {
 	int ret;
 	int pageblock_mt, page_mt;
+	struct stack_trace trace;
 	char *kbuf;
 
 	kbuf = kmalloc(count, GFP_KERNEL);
@@ -121,8 +122,10 @@ print_page_owner(char __user *buf, size_t count, unsigned long pfn,
 	if (ret >= count)
 		goto err;
 
-	ret += snprint_stack_trace(kbuf + ret, count - ret,
-					&page_ext->trace, 0);
+	trace.nr_entries = page_ext->nr_entries;
+	trace.entries = &page_ext->trace_entries[0];
+
+	ret += snprint_stack_trace(kbuf + ret, count - ret, &trace, 0);
 	if (ret >= count)
 		goto err;
 
-- 
1.9.1


^ permalink raw reply related	[flat|nested] 5+ messages in thread
* Re: [PATCH 1/1] mm/page_ext: remove unnecessary stack_trace field
  2015-01-26 21:52 ` [PATCH 1/1] " Sergei Rogachev
@ 2015-01-27  8:36   ` Joonsoo Kim
  2015-01-27 22:43   ` Andrew Morton
  1 sibling, 0 replies; 5+ messages in thread
From: Joonsoo Kim @ 2015-01-27  8:36 UTC (permalink / raw)
  To: Sergei Rogachev; +Cc: akpm, LKML

On Tue, Jan 27, 2015 at 12:52:12AM +0300, Sergei Rogachev wrote:
> Page owner uses the page_ext structure to keep meta-information
> for every page in the system. The structure also contains a field
> of type 'struct stack_trace', page owner uses this field during
> invocation of the function save_stack_trace. It is easy to notice
> that keeping a copy of this structure for every page in the system
> is very inefficiently in terms of memory.
> 
> The patch removes this unnecessary field of page_ext and forces
> page owner to use a stack_trace structure allocated on the stack.
> 
> Signed-off-by: Sergei Rogachev <rogachevsergei@gmail.com>
> ---
>  include/linux/page_ext.h |  2 +-
>  mm/page_owner.c          | 21 ++++++++++++---------
>  2 files changed, 13 insertions(+), 10 deletions(-)
> 
> diff --git a/include/linux/page_ext.h b/include/linux/page_ext.h
> index d2a2c84..c42981c 100644
> --- a/include/linux/page_ext.h
> +++ b/include/linux/page_ext.h
> @@ -40,7 +40,7 @@ struct page_ext {
>  #ifdef CONFIG_PAGE_OWNER
>  	unsigned int order;
>  	gfp_t gfp_mask;
> -	struct stack_trace trace;
> +	unsigned int nr_entries;
>  	unsigned long trace_entries[8];
>  #endif
>  };
> diff --git a/mm/page_owner.c b/mm/page_owner.c
> index 9ab4a9b..f7f3318 100644
> --- a/mm/page_owner.c
> +++ b/mm/page_owner.c
> @@ -60,19 +60,19 @@ void __reset_page_owner(struct page *page, unsigned int order)
>  void __set_page_owner(struct page *page, unsigned int order, gfp_t gfp_mask)
>  {
>  	struct page_ext *page_ext;
> -	struct stack_trace *trace;
> +	struct stack_trace trace;
>  
>  	page_ext = lookup_page_ext(page);
>  
> -	trace = &page_ext->trace;
> -	trace->nr_entries = 0;
> -	trace->max_entries = ARRAY_SIZE(page_ext->trace_entries);
> -	trace->entries = &page_ext->trace_entries[0];
> -	trace->skip = 3;
> -	save_stack_trace(&page_ext->trace);
> +	trace.nr_entries = 0;
> +	trace.max_entries = ARRAY_SIZE(page_ext->trace_entries);
> +	trace.entries = &page_ext->trace_entries[0];
> +	trace.skip = 3;
> +	save_stack_trace(&trace);
>  
>  	page_ext->order = order;
>  	page_ext->gfp_mask = gfp_mask;
> +	page_ext->nr_entries = trace.nr_entries;
>  
>  	__set_bit(PAGE_EXT_OWNER, &page_ext->flags);
>  }
> @@ -83,6 +83,7 @@ print_page_owner(char __user *buf, size_t count, unsigned long pfn,
>  {
>  	int ret;
>  	int pageblock_mt, page_mt;
> +	struct stack_trace trace;
>  	char *kbuf;
>  
>  	kbuf = kmalloc(count, GFP_KERNEL);
> @@ -121,8 +122,10 @@ print_page_owner(char __user *buf, size_t count, unsigned long pfn,
>  	if (ret >= count)
>  		goto err;
>  
> -	ret += snprint_stack_trace(kbuf + ret, count - ret,
> -					&page_ext->trace, 0);
> +	trace.nr_entries = page_ext->nr_entries;
> +	trace.entries = &page_ext->trace_entries[0];
> +
> +	ret += snprint_stack_trace(kbuf + ret, count - ret, &trace, 0);
>  	if (ret >= count)
>  		goto err;


Acked-by: Joonsoo Kim <iamjoonsoo.kim@lge.com>

Thanks.

^ permalink raw reply	[flat|nested] 5+ messages in thread
* Re: [PATCH 1/1] mm/page_ext: remove unnecessary stack_trace field
  2015-01-26 21:52 ` [PATCH 1/1] " Sergei Rogachev
  2015-01-27  8:36   ` Joonsoo Kim
@ 2015-01-27 22:43   ` Andrew Morton
  2015-01-28 19:08     ` Sergei Rogachev
  1 sibling, 1 reply; 5+ messages in thread
From: Andrew Morton @ 2015-01-27 22:43 UTC (permalink / raw)
  To: Sergei Rogachev; +Cc: iamjoonsoo.kim, LKML

On Tue, 27 Jan 2015 00:52:12 +0300 Sergei Rogachev <rogachevsergei@gmail.com> wrote:

> Page owner uses the page_ext structure to keep meta-information
> for every page in the system. The structure also contains a field
> of type 'struct stack_trace', page owner uses this field during
> invocation of the function save_stack_trace. It is easy to notice
> that keeping a copy of this structure for every page in the system
> is very inefficiently in terms of memory.
> 
> The patch removes this unnecessary field of page_ext and forces
> page owner to use a stack_trace structure allocated on the stack.
> 

Fair enough.

What do you think of the below tweaks?  Seems a bit neater, and it will
cause all unmentioned fields to be zeroed out.  It's not a bug to leave
.max_entries uninitialised in print_page_owner(), but it's nice not to
leave loose ends.

--- a/mm/page_owner.c~mm-page_ext-remove-unnecessary-stack_trace-field-fix
+++ a/mm/page_owner.c
@@ -59,15 +59,14 @@ void __reset_page_owner(struct page *pag
 
 void __set_page_owner(struct page *page, unsigned int order, gfp_t gfp_mask)
 {
-	struct page_ext *page_ext;
-	struct stack_trace trace;
+	struct page_ext *page_ext = lookup_page_ext(page);
+	struct stack_trace trace = {
+		.nr_entries = 0,
+		.max_entries = ARRAY_SIZE(page_ext->trace_entries),
+		.entries = &page_ext->trace_entries[0],
+		.skip = 3,
+	};
 
-	page_ext = lookup_page_ext(page);
-
-	trace.nr_entries = 0;
-	trace.max_entries = ARRAY_SIZE(page_ext->trace_entries);
-	trace.entries = &page_ext->trace_entries[0];
-	trace.skip = 3;
 	save_stack_trace(&trace);
 
 	page_ext->order = order;
@@ -83,8 +82,11 @@ print_page_owner(char __user *buf, size_
 {
 	int ret;
 	int pageblock_mt, page_mt;
-	struct stack_trace trace;
 	char *kbuf;
+	struct stack_trace trace = {
+		.nr_entries = page_ext->nr_entries,
+		.entries = &page_ext->trace_entries[0],
+	};
 
 	kbuf = kmalloc(count, GFP_KERNEL);
 	if (!kbuf)
@@ -122,9 +124,6 @@ print_page_owner(char __user *buf, size_
 	if (ret >= count)
 		goto err;
 
-	trace.nr_entries = page_ext->nr_entries;
-	trace.entries = &page_ext->trace_entries[0];
-
 	ret += snprint_stack_trace(kbuf + ret, count - ret, &trace, 0);
 	if (ret >= count)
 		goto err;
_


^ permalink raw reply	[flat|nested] 5+ messages in thread
* Re: [PATCH 1/1] mm/page_ext: remove unnecessary stack_trace field
  2015-01-27 22:43   ` Andrew Morton
@ 2015-01-28 19:08     ` Sergei Rogachev
  0 siblings, 0 replies; 5+ messages in thread
From: Sergei Rogachev @ 2015-01-28 19:08 UTC (permalink / raw)
  To: Andrew Morton; +Cc: iamjoonsoo.kim, LKML

On Tue, 27 Jan 2015 14:43:19 -0800
Andrew Morton <akpm@linux-foundation.org> wrote:

> On Tue, 27 Jan 2015 00:52:12 +0300 Sergei Rogachev <rogachevsergei@gmail.com> wrote:
> 
> > Page owner uses the page_ext structure to keep meta-information
> > for every page in the system. The structure also contains a field
> > of type 'struct stack_trace', page owner uses this field during
> > invocation of the function save_stack_trace. It is easy to notice
> > that keeping a copy of this structure for every page in the system
> > is very inefficiently in terms of memory.
> > 
> > The patch removes this unnecessary field of page_ext and forces
> > page owner to use a stack_trace structure allocated on the stack.
> > 
> 
> Fair enough.
> 
> What do you think of the below tweaks?  Seems a bit neater, and it will
> cause all unmentioned fields to be zeroed out.  It's not a bug to leave
> .max_entries uninitialised in print_page_owner(), but it's nice not to
> leave loose ends.

Yes, with your fix the code looks much better!

> 
> --- a/mm/page_owner.c~mm-page_ext-remove-unnecessary-stack_trace-field-fix
> +++ a/mm/page_owner.c
> @@ -59,15 +59,14 @@ void __reset_page_owner(struct page *pag
>  
>  void __set_page_owner(struct page *page, unsigned int order, gfp_t gfp_mask)
>  {
> -	struct page_ext *page_ext;
> -	struct stack_trace trace;
> +	struct page_ext *page_ext = lookup_page_ext(page);
> +	struct stack_trace trace = {
> +		.nr_entries = 0,
> +		.max_entries = ARRAY_SIZE(page_ext->trace_entries),
> +		.entries = &page_ext->trace_entries[0],
> +		.skip = 3,
> +	};
>  
> -	page_ext = lookup_page_ext(page);
> -
> -	trace.nr_entries = 0;
> -	trace.max_entries = ARRAY_SIZE(page_ext->trace_entries);
> -	trace.entries = &page_ext->trace_entries[0];
> -	trace.skip = 3;
>  	save_stack_trace(&trace);
>  
>  	page_ext->order = order;
> @@ -83,8 +82,11 @@ print_page_owner(char __user *buf, size_
>  {
>  	int ret;
>  	int pageblock_mt, page_mt;
> -	struct stack_trace trace;
>  	char *kbuf;
> +	struct stack_trace trace = {
> +		.nr_entries = page_ext->nr_entries,
> +		.entries = &page_ext->trace_entries[0],
> +	};
>  
>  	kbuf = kmalloc(count, GFP_KERNEL);
>  	if (!kbuf)
> @@ -122,9 +124,6 @@ print_page_owner(char __user *buf, size_
>  	if (ret >= count)
>  		goto err;
>  
> -	trace.nr_entries = page_ext->nr_entries;
> -	trace.entries = &page_ext->trace_entries[0];
> -
>  	ret += snprint_stack_trace(kbuf + ret, count - ret, &trace, 0);
>  	if (ret >= count)
>  		goto err;
> _
> 

^ permalink raw reply	[flat|nested] 5+ messages in thread
end of thread, other threads:[~2015-01-28 20:58 UTC | newest]

Thread overview: 5+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2015-01-26 21:52 [PATCH 0/1] mm/page_ext: remove unnecessary stack_trace field Sergei Rogachev
2015-01-26 21:52 ` [PATCH 1/1] " Sergei Rogachev
2015-01-27  8:36   ` Joonsoo Kim
2015-01-27 22:43   ` Andrew Morton
2015-01-28 19:08     ` Sergei Rogachev

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