[PATCH RESEND] mm/vmscan : use vmcan_swappiness( ) basing on MEMCG config to elimiate unnecessary runtime cost

[PATCH RESEND] mm/vmscan : use vmcan_swappiness( ) basing on MEMCG config to elimiate unnecessary runtime cost

[larmbr]

Currently, we get the vm_swappiness via vmscan_swappiness(), which
calls global_reclaim() to check if this is a global reclaim. 

Besides, the current implementation of global_reclaim() always returns 
true for the !CONFIG_MEGCG case, and judges the other case by checking 
whether scan_control->target_mem_cgroup is null or not.

Thus, we could just use two versions of vmscan_swappiness() based on 
MEMCG Kconfig , to eliminate the unnecessary run-time cost for 
the !CONFIG_MEMCG at all, and to squash all memcg-related checking
into the CONFIG_MEMCG version.

Signed-off-by: Zhan Jianyu <nasa4836@gmail.com>
---
mm/memcontrol.c |    6 +++++-
mm/vmscan.c     |    9 +++++++--
2 files changed, 12 insertions(+), 3 deletions(-)


diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index c5792a5..1290320 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -1525,9 +1525,13 @@ static unsigned long mem_cgroup_margin(struct mem_cgroup *memcg)
 
 int mem_cgroup_swappiness(struct mem_cgroup *memcg)
 {
-	struct cgroup *cgrp = memcg->css.cgroup;
+	struct cgroup *cgrp;
+
+	if (!memcg)
+		return vm_swappiness;
 
 	/* root ? */
+	cgrp = memcg->css.cgroup;
 	if (cgrp->parent == NULL)
 		return vm_swappiness;
 
diff --git a/mm/vmscan.c b/mm/vmscan.c
index 2cff0d4..1de652d 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -1742,12 +1742,17 @@ static unsigned long shrink_list(enum lru_list lru, unsigned long nr_to_scan,
 	return shrink_inactive_list(nr_to_scan, lruvec, sc, lru);
 }
 
+#ifdef CONFIG_MEMCG
 static int vmscan_swappiness(struct scan_control *sc)
 {
-	if (global_reclaim(sc))
-		return vm_swappiness;
 	return mem_cgroup_swappiness(sc->target_mem_cgroup);
 }
+#else
+static int vmscan_swappiness(struct scan_control *sc)
+{
+	return vm_swappiness;
+}
+#endif
 
 enum scan_balance {
 	SCAN_EQUAL,

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Re: [PATCH RESEND] mm/vmscan : use vmcan_swappiness( ) basing on MEMCG config to elimiate unnecessary runtime cost

[Naoya Horiguchi]

Please fix a typo in subject line (which affects how easy we can access
paticular patches later with grepping subject lines.)

Reviewed-by: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>

On Mon, Aug 26, 2013 at 09:36:58PM +0800, larmbr wrote:
> Currently, we get the vm_swappiness via vmscan_swappiness(), which
> calls global_reclaim() to check if this is a global reclaim. 
> 
> Besides, the current implementation of global_reclaim() always returns 
> true for the !CONFIG_MEGCG case, and judges the other case by checking 
> whether scan_control->target_mem_cgroup is null or not.
> 
> Thus, we could just use two versions of vmscan_swappiness() based on 
> MEMCG Kconfig , to eliminate the unnecessary run-time cost for 
> the !CONFIG_MEMCG at all, and to squash all memcg-related checking
> into the CONFIG_MEMCG version.
> 
> Signed-off-by: Zhan Jianyu <nasa4836@gmail.com>
> ---
> mm/memcontrol.c |    6 +++++-
> mm/vmscan.c     |    9 +++++++--
> 2 files changed, 12 insertions(+), 3 deletions(-)
> 
> 
> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> index c5792a5..1290320 100644
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -1525,9 +1525,13 @@ static unsigned long mem_cgroup_margin(struct mem_cgroup *memcg)
>  
>  int mem_cgroup_swappiness(struct mem_cgroup *memcg)
>  {
> -	struct cgroup *cgrp = memcg->css.cgroup;
> +	struct cgroup *cgrp;
> +
> +	if (!memcg)
> +		return vm_swappiness;
>  
>  	/* root ? */
> +	cgrp = memcg->css.cgroup;
>  	if (cgrp->parent == NULL)
>  		return vm_swappiness;
>  
> diff --git a/mm/vmscan.c b/mm/vmscan.c
> index 2cff0d4..1de652d 100644
> --- a/mm/vmscan.c
> +++ b/mm/vmscan.c
> @@ -1742,12 +1742,17 @@ static unsigned long shrink_list(enum lru_list lru, unsigned long nr_to_scan,
>  	return shrink_inactive_list(nr_to_scan, lruvec, sc, lru);
>  }
>  
> +#ifdef CONFIG_MEMCG
>  static int vmscan_swappiness(struct scan_control *sc)
>  {
> -	if (global_reclaim(sc))
> -		return vm_swappiness;
>  	return mem_cgroup_swappiness(sc->target_mem_cgroup);
>  }
> +#else
> +static int vmscan_swappiness(struct scan_control *sc)
> +{
> +	return vm_swappiness;
> +}
> +#endif
>  
>  enum scan_balance {
>  	SCAN_EQUAL,
> 
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Re: [PATCH RESEND] mm/vmscan : use vmcan_swappiness( ) basing on MEMCG config to elimiate unnecessary runtime cost

[Johannes Weiner]

On Mon, Aug 26, 2013 at 09:36:58PM +0800, larmbr wrote:
> Currently, we get the vm_swappiness via vmscan_swappiness(), which
> calls global_reclaim() to check if this is a global reclaim. 
> 
> Besides, the current implementation of global_reclaim() always returns 
> true for the !CONFIG_MEGCG case, and judges the other case by checking 
> whether scan_control->target_mem_cgroup is null or not.
> 
> Thus, we could just use two versions of vmscan_swappiness() based on 
> MEMCG Kconfig , to eliminate the unnecessary run-time cost for 
> the !CONFIG_MEMCG at all, and to squash all memcg-related checking
> into the CONFIG_MEMCG version.

The compiler can easily detect that global_reclaim() always returns
true for !CONFIG_MEMCG during compile time and not even generate a
branch for this.

> 2 files changed, 12 insertions(+), 3 deletions(-)

You're adding more code for now gain.

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Re: [PATCH RESEND] mm/vmscan : use vmcan_swappiness( ) basing on MEMCG config to elimiate unnecessary runtime cost

[Zhan Jianyu]

On Wed, Sep 4, 2013 at 6:47 AM, Johannes Weiner <hannes@cmpxchg.org> wrote:
> On Mon, Aug 26, 2013 at 09:36:58PM +0800, larmbr wrote:
>> Currently, we get the vm_swappiness via vmscan_swappiness(), which
>> calls global_reclaim() to check if this is a global reclaim.
>>
>> Besides, the current implementation of global_reclaim() always returns
>> true for the !CONFIG_MEGCG case, and judges the other case by checking
>> whether scan_control->target_mem_cgroup is null or not.
>>
>> Thus, we could just use two versions of vmscan_swappiness() based on
>> MEMCG Kconfig , to eliminate the unnecessary run-time cost for
>> the !CONFIG_MEMCG at all, and to squash all memcg-related checking
>> into the CONFIG_MEMCG version.
>
> The compiler can easily detect that global_reclaim() always returns
> true for !CONFIG_MEMCG during compile time and not even generate a
> branch for this.
>

Hi, Johannes Weiner,

Thanks for your comment ;)

Andrew has pointed this out and this patch is abandoned.


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Regards,
Zhan Jianyu

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