[PATCH v2] page_cgroup: add helper function to get swap_cgroup

[PATCH v2] page_cgroup: add helper function to get swap_cgroup

[Bob Liu]

There are multi places need to get swap_cgroup, so add a helper
function:
static struct swap_cgroup *swap_cgroup_getsc(swp_entry_t ent,
                                struct swap_cgroup_ctrl **ctrl);
to simple the code.

v1 -> v2:
 - add parameter struct swap_cgroup_ctrl **ctrl suggested by Michal

Signed-off-by: Bob Liu <lliubbo@gmail.com>
---
 mm/page_cgroup.c |   57 ++++++++++++++++++++++-------------------------------
 1 files changed, 24 insertions(+), 33 deletions(-)

diff --git a/mm/page_cgroup.c b/mm/page_cgroup.c
index f0559e0..1970e8a 100644
--- a/mm/page_cgroup.c
+++ b/mm/page_cgroup.c
@@ -362,6 +362,27 @@ not_enough_page:
 	return -ENOMEM;
 }
 
+static struct swap_cgroup *swap_cgroup_getsc(swp_entry_t ent,
+					struct swap_cgroup_ctrl **ctrl)
+{
+	int type = swp_type(ent);
+	unsigned long offset = swp_offset(ent);
+	unsigned long idx = offset / SC_PER_PAGE;
+	unsigned long pos = offset & SC_POS_MASK;
+	struct swap_cgroup_ctrl *temp_ctrl;
+	struct page *mappage;
+	struct swap_cgroup *sc;
+
+	temp_ctrl = &swap_cgroup_ctrl[type];
+	if (ctrl)
+		*ctrl = temp_ctrl;
+
+	mappage = temp_ctrl->map[idx];
+	sc = page_address(mappage);
+	sc += pos;
+	return sc;
+}
+
 /**
  * swap_cgroup_cmpxchg - cmpxchg mem_cgroup's id for this swp_entry.
  * @end: swap entry to be cmpxchged
@@ -374,21 +395,13 @@ not_enough_page:
 unsigned short swap_cgroup_cmpxchg(swp_entry_t ent,
 					unsigned short old, unsigned short new)
 {
-	int type = swp_type(ent);
-	unsigned long offset = swp_offset(ent);
-	unsigned long idx = offset / SC_PER_PAGE;
-	unsigned long pos = offset & SC_POS_MASK;
 	struct swap_cgroup_ctrl *ctrl;
-	struct page *mappage;
 	struct swap_cgroup *sc;
 	unsigned long flags;
 	unsigned short retval;
 
-	ctrl = &swap_cgroup_ctrl[type];
+	sc = swap_cgroup_getsc(ent, &ctrl);
 
-	mappage = ctrl->map[idx];
-	sc = page_address(mappage);
-	sc += pos;
 	spin_lock_irqsave(&ctrl->lock, flags);
 	retval = sc->id;
 	if (retval == old)
@@ -409,21 +422,13 @@ unsigned short swap_cgroup_cmpxchg(swp_entry_t ent,
  */
 unsigned short swap_cgroup_record(swp_entry_t ent, unsigned short id)
 {
-	int type = swp_type(ent);
-	unsigned long offset = swp_offset(ent);
-	unsigned long idx = offset / SC_PER_PAGE;
-	unsigned long pos = offset & SC_POS_MASK;
 	struct swap_cgroup_ctrl *ctrl;
-	struct page *mappage;
 	struct swap_cgroup *sc;
 	unsigned short old;
 	unsigned long flags;
 
-	ctrl = &swap_cgroup_ctrl[type];
+	sc = swap_cgroup_getsc(ent, &ctrl);
 
-	mappage = ctrl->map[idx];
-	sc = page_address(mappage);
-	sc += pos;
 	spin_lock_irqsave(&ctrl->lock, flags);
 	old = sc->id;
 	sc->id = id;
@@ -440,21 +445,7 @@ unsigned short swap_cgroup_record(swp_entry_t ent, unsigned short id)
  */
 unsigned short lookup_swap_cgroup(swp_entry_t ent)
 {
-	int type = swp_type(ent);
-	unsigned long offset = swp_offset(ent);
-	unsigned long idx = offset / SC_PER_PAGE;
-	unsigned long pos = offset & SC_POS_MASK;
-	struct swap_cgroup_ctrl *ctrl;
-	struct page *mappage;
-	struct swap_cgroup *sc;
-	unsigned short ret;
-
-	ctrl = &swap_cgroup_ctrl[type];
-	mappage = ctrl->map[idx];
-	sc = page_address(mappage);
-	sc += pos;
-	ret = sc->id;
-	return ret;
+	return swap_cgroup_getsc(ent, NULL)->id;
 }
 
 int swap_cgroup_swapon(int type, unsigned long max_pages)
-- 
1.7.0.4


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Re: [PATCH v2] page_cgroup: add helper function to get swap_cgroup

[Michal Hocko]

On Fri 02-12-11 18:40:27, Bob Liu wrote:
> There are multi places need to get swap_cgroup, so add a helper
> function:
> static struct swap_cgroup *swap_cgroup_getsc(swp_entry_t ent,
>                                 struct swap_cgroup_ctrl **ctrl);
> to simple the code.
> 
> v1 -> v2:
>  - add parameter struct swap_cgroup_ctrl **ctrl suggested by Michal
> 
> Signed-off-by: Bob Liu <lliubbo@gmail.com>

Thanks.

Acked-by: Michal Hocko <mhocko@suse.cz>

> ---
>  mm/page_cgroup.c |   57 ++++++++++++++++++++++-------------------------------
>  1 files changed, 24 insertions(+), 33 deletions(-)
> 
> diff --git a/mm/page_cgroup.c b/mm/page_cgroup.c
> index f0559e0..1970e8a 100644
> --- a/mm/page_cgroup.c
> +++ b/mm/page_cgroup.c
> @@ -362,6 +362,27 @@ not_enough_page:
>  	return -ENOMEM;
>  }
>  
> +static struct swap_cgroup *swap_cgroup_getsc(swp_entry_t ent,
> +					struct swap_cgroup_ctrl **ctrl)
> +{
> +	int type = swp_type(ent);
> +	unsigned long offset = swp_offset(ent);
> +	unsigned long idx = offset / SC_PER_PAGE;
> +	unsigned long pos = offset & SC_POS_MASK;
> +	struct swap_cgroup_ctrl *temp_ctrl;
> +	struct page *mappage;
> +	struct swap_cgroup *sc;
> +
> +	temp_ctrl = &swap_cgroup_ctrl[type];
> +	if (ctrl)
> +		*ctrl = temp_ctrl;
> +
> +	mappage = temp_ctrl->map[idx];
> +	sc = page_address(mappage);
> +	sc += pos;
> +	return sc;
> +}
> +
>  /**
>   * swap_cgroup_cmpxchg - cmpxchg mem_cgroup's id for this swp_entry.
>   * @end: swap entry to be cmpxchged
> @@ -374,21 +395,13 @@ not_enough_page:
>  unsigned short swap_cgroup_cmpxchg(swp_entry_t ent,
>  					unsigned short old, unsigned short new)
>  {
> -	int type = swp_type(ent);
> -	unsigned long offset = swp_offset(ent);
> -	unsigned long idx = offset / SC_PER_PAGE;
> -	unsigned long pos = offset & SC_POS_MASK;
>  	struct swap_cgroup_ctrl *ctrl;
> -	struct page *mappage;
>  	struct swap_cgroup *sc;
>  	unsigned long flags;
>  	unsigned short retval;
>  
> -	ctrl = &swap_cgroup_ctrl[type];
> +	sc = swap_cgroup_getsc(ent, &ctrl);
>  
> -	mappage = ctrl->map[idx];
> -	sc = page_address(mappage);
> -	sc += pos;
>  	spin_lock_irqsave(&ctrl->lock, flags);
>  	retval = sc->id;
>  	if (retval == old)
> @@ -409,21 +422,13 @@ unsigned short swap_cgroup_cmpxchg(swp_entry_t ent,
>   */
>  unsigned short swap_cgroup_record(swp_entry_t ent, unsigned short id)
>  {
> -	int type = swp_type(ent);
> -	unsigned long offset = swp_offset(ent);
> -	unsigned long idx = offset / SC_PER_PAGE;
> -	unsigned long pos = offset & SC_POS_MASK;
>  	struct swap_cgroup_ctrl *ctrl;
> -	struct page *mappage;
>  	struct swap_cgroup *sc;
>  	unsigned short old;
>  	unsigned long flags;
>  
> -	ctrl = &swap_cgroup_ctrl[type];
> +	sc = swap_cgroup_getsc(ent, &ctrl);
>  
> -	mappage = ctrl->map[idx];
> -	sc = page_address(mappage);
> -	sc += pos;
>  	spin_lock_irqsave(&ctrl->lock, flags);
>  	old = sc->id;
>  	sc->id = id;
> @@ -440,21 +445,7 @@ unsigned short swap_cgroup_record(swp_entry_t ent, unsigned short id)
>   */
>  unsigned short lookup_swap_cgroup(swp_entry_t ent)
>  {
> -	int type = swp_type(ent);
> -	unsigned long offset = swp_offset(ent);
> -	unsigned long idx = offset / SC_PER_PAGE;
> -	unsigned long pos = offset & SC_POS_MASK;
> -	struct swap_cgroup_ctrl *ctrl;
> -	struct page *mappage;
> -	struct swap_cgroup *sc;
> -	unsigned short ret;
> -
> -	ctrl = &swap_cgroup_ctrl[type];
> -	mappage = ctrl->map[idx];
> -	sc = page_address(mappage);
> -	sc += pos;
> -	ret = sc->id;
> -	return ret;
> +	return swap_cgroup_getsc(ent, NULL)->id;
>  }
>  
>  int swap_cgroup_swapon(int type, unsigned long max_pages)
> -- 
> 1.7.0.4
> 
> 
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-- 
Michal Hocko
SUSE Labs
SUSE LINUX s.r.o.
Lihovarska 1060/12
190 00 Praha 9    
Czech Republic

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Re: [PATCH v2] page_cgroup: add helper function to get swap_cgroup

[KAMEZAWA Hiroyuki]

On Fri, 2 Dec 2011 18:40:27 +0800
Bob Liu <lliubbo@gmail.com> wrote:

> There are multi places need to get swap_cgroup, so add a helper
> function:
> static struct swap_cgroup *swap_cgroup_getsc(swp_entry_t ent,
>                                 struct swap_cgroup_ctrl **ctrl);
> to simple the code.
> 
> v1 -> v2:
>  - add parameter struct swap_cgroup_ctrl **ctrl suggested by Michal
> 
> Signed-off-by: Bob Liu <lliubbo@gmail.com>

Acked-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>

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Re: [PATCH v2] page_cgroup: add helper function to get swap_cgroup

[Johannes Weiner]

On Fri, Dec 02, 2011 at 06:40:27PM +0800, Bob Liu wrote:
> There are multi places need to get swap_cgroup, so add a helper
> function:
> static struct swap_cgroup *swap_cgroup_getsc(swp_entry_t ent,
>                                 struct swap_cgroup_ctrl **ctrl);
> to simple the code.
> 
> v1 -> v2:
>  - add parameter struct swap_cgroup_ctrl **ctrl suggested by Michal
> 
> Signed-off-by: Bob Liu <lliubbo@gmail.com>
> ---
>  mm/page_cgroup.c |   57 ++++++++++++++++++++++-------------------------------
>  1 files changed, 24 insertions(+), 33 deletions(-)
> 
> diff --git a/mm/page_cgroup.c b/mm/page_cgroup.c
> index f0559e0..1970e8a 100644
> --- a/mm/page_cgroup.c
> +++ b/mm/page_cgroup.c
> @@ -362,6 +362,27 @@ not_enough_page:
>  	return -ENOMEM;
>  }

I realize that you mostly moved what was already there, but there are
a couple more things to clean up.  Would you like to send a patch for
them as well?

> +static struct swap_cgroup *swap_cgroup_getsc(swp_entry_t ent,
> +					struct swap_cgroup_ctrl **ctrl)

__lookup_swap_cgroup()?  Or even more matching names would be to have
that public interface called lookup_swap_cgroup_id() and let this one
be lookup_swap_cgroup().

> +{
> +	int type = swp_type(ent);

swp_type() returns unsigned int

> +	unsigned long offset = swp_offset(ent);

swp_offset() returns pgoff_t

> +	unsigned long idx = offset / SC_PER_PAGE;
> +	unsigned long pos = offset & SC_POS_MASK;

This is actually quite crappy, the definition looks like this:

#define SC_PER_PAGE	(PAGE_SIZE/sizeof(struct swap_cgroup))
#define SC_POS_MASK	(SC_PER_PAGE - 1)

which relies on the fact that the division named SC_PER_PAGE yields a
power of two, which only is true by accident.

Better would be to delete SC_POS_MASK and use offset % SC_PER_PAGE
instead.

> +	struct swap_cgroup_ctrl *temp_ctrl;
> +	struct page *mappage;
> +	struct swap_cgroup *sc;
> +
> +	temp_ctrl = &swap_cgroup_ctrl[type];
> +	if (ctrl)
> +		*ctrl = temp_ctrl;

Name the output parameter ctrlp instead?  Then you can call the local
one ctrl.

Also, type is only used once, better to just inline it:

	&swap_cgroup_ctrl[swp_type(ent)]

> +	mappage = temp_ctrl->map[idx];

Same for idx, just use ctrl->map[offset / SC_PER_PAGE] directly.

> +	sc = page_address(mappage);
> +	sc += pos;
> +	return sc;
> +}

That seems elaborate.

	return page_address(mappage) + offset % SC_PER_PAGE

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