[PATCH] mm: page_owner: fetch backtrace only for tracked pages

[PATCH] mm: page_owner: fetch backtrace only for tracked pages

[Sergei Trofimovich]

Very minor optimization.

CC: Andrew Morton <akpm@linux-foundation.org>
CC: linux-mm@kvack.org
Signed-off-by: Sergei Trofimovich <slyfox@gentoo.org>
---
 mm/page_owner.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/mm/page_owner.c b/mm/page_owner.c
index 63e4ecaba97b..7147fd34a948 100644
--- a/mm/page_owner.c
+++ b/mm/page_owner.c
@@ -140,14 +140,14 @@ void __reset_page_owner(struct page *page, unsigned int order)
 {
 	int i;
 	struct page_ext *page_ext;
-	depot_stack_handle_t handle = 0;
+	depot_stack_handle_t handle;
 	struct page_owner *page_owner;
 
-	handle = save_stack(GFP_NOWAIT | __GFP_NOWARN);
-
 	page_ext = lookup_page_ext(page);
 	if (unlikely(!page_ext))
 		return;
+
+	handle = save_stack(GFP_NOWAIT | __GFP_NOWARN);
 	for (i = 0; i < (1 << order); i++) {
 		__clear_bit(PAGE_EXT_OWNER_ALLOCATED, &page_ext->flags);
 		page_owner = get_page_owner(page_ext);
-- 
2.31.1

Re: [PATCH] mm: page_owner: fetch backtrace only for tracked pages

[Vlastimil Babka]

On 4/1/21 11:24 PM, Sergei Trofimovich wrote:
> Very minor optimization.

I'm not entirely sure about accuracy of "only for tracked pages". Missing
page_ext is something I'm not even sure how possible it is in practice, probably
just an error condition (failed to be allocated?). Or did you observe this in
practice? But anyway, the change is not wrong.

> CC: Andrew Morton <akpm@linux-foundation.org>
> CC: linux-mm@kvack.org
> Signed-off-by: Sergei Trofimovich <slyfox@gentoo.org>

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

> ---
>  mm/page_owner.c | 6 +++---
>  1 file changed, 3 insertions(+), 3 deletions(-)
> 
> diff --git a/mm/page_owner.c b/mm/page_owner.c
> index 63e4ecaba97b..7147fd34a948 100644
> --- a/mm/page_owner.c
> +++ b/mm/page_owner.c
> @@ -140,14 +140,14 @@ void __reset_page_owner(struct page *page, unsigned int order)
>  {
>  	int i;
>  	struct page_ext *page_ext;
> -	depot_stack_handle_t handle = 0;
> +	depot_stack_handle_t handle;
>  	struct page_owner *page_owner;
>  
> -	handle = save_stack(GFP_NOWAIT | __GFP_NOWARN);
> -
>  	page_ext = lookup_page_ext(page);
>  	if (unlikely(!page_ext))
>  		return;
> +
> +	handle = save_stack(GFP_NOWAIT | __GFP_NOWARN);
>  	for (i = 0; i < (1 << order); i++) {
>  		__clear_bit(PAGE_EXT_OWNER_ALLOCATED, &page_ext->flags);
>  		page_owner = get_page_owner(page_ext);
> 

Re: [PATCH] mm: page_owner: fetch backtrace only for tracked pages

[Sergei Trofimovich]

On Wed, Apr 07, 2021 at 05:49:14PM +0200, Vlastimil Babka wrote:
> On 4/1/21 11:24 PM, Sergei Trofimovich wrote:
> > Very minor optimization.
> 
> I'm not entirely sure about accuracy of "only for tracked pages". Missing
> page_ext is something I'm not even sure how possible it is in practice, probably
> just an error condition (failed to be allocated?). Or did you observe this in
> practice? But anyway, the change is not wrong.

Never saw missing 'page_ext' in practice (I also did not check for
it explicitly). I agree "optimization" is misleading. "cleanup"
might be a better wording.

> > CC: Andrew Morton <akpm@linux-foundation.org>
> > CC: linux-mm@kvack.org
> > Signed-off-by: Sergei Trofimovich <slyfox@gentoo.org>
> 
> Acked-by: Vlastimil Babka <vbabka@suse.cz>
> 
> > ---
> >  mm/page_owner.c | 6 +++---
> >  1 file changed, 3 insertions(+), 3 deletions(-)
> > 
> > diff --git a/mm/page_owner.c b/mm/page_owner.c
> > index 63e4ecaba97b..7147fd34a948 100644
> > --- a/mm/page_owner.c
> > +++ b/mm/page_owner.c
> > @@ -140,14 +140,14 @@ void __reset_page_owner(struct page *page, unsigned int order)
> >  {
> >  	int i;
> >  	struct page_ext *page_ext;
> > -	depot_stack_handle_t handle = 0;
> > +	depot_stack_handle_t handle;
> >  	struct page_owner *page_owner;
> >  
> > -	handle = save_stack(GFP_NOWAIT | __GFP_NOWARN);
> > -
> >  	page_ext = lookup_page_ext(page);
> >  	if (unlikely(!page_ext))
> >  		return;
> > +
> > +	handle = save_stack(GFP_NOWAIT | __GFP_NOWARN);
> >  	for (i = 0; i < (1 << order); i++) {
> >  		__clear_bit(PAGE_EXT_OWNER_ALLOCATED, &page_ext->flags);
> >  		page_owner = get_page_owner(page_ext);
> > 
> 

-- 

  Sergei