Re: [PATCH 3/9] mm, page_alloc: remove setup_pageset()

[Vlastimil Babka]

On 10/5/20 2:59 PM, Michal Hocko wrote:

On Tue 22-09-20 16:37:06, Vlastimil Babka wrote:

We initialize boot-time pagesets with setup_pageset(), which sets high and
batch values that effectively disable pcplists.

We can remove this wrapper if we just set these values for all pagesets in
pageset_init(). Non-boot pagesets then subsequently update them to the proper
values.

No functional change.

Signed-off-by: Vlastimil Babka 
---
 mm/page_alloc.c | 17 ++---
 1 file changed, 10 insertions(+), 7 deletions(-)

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 26069c8d1b19..76c2b4578723 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -5823,7 +5823,7 @@ static void build_zonelists(pg_data_t *pgdat)
  * not check if the processor is online before following the pageset pointer.
  * Other parts of the kernel may not check if the zone is available.
  */
-static void setup_pageset(struct per_cpu_pageset *p);
+static void pageset_init(struct per_cpu_pageset *p);
 static DEFINE_PER_CPU(struct per_cpu_pageset, boot_pageset);
 static DEFINE_PER_CPU(struct per_cpu_nodestat, boot_nodestats);
 
@@ -5891,7 +5891,7 @@ build_all_zonelists_init(void)

 * (a chicken-egg dilemma).
 */
for_each_possible_cpu(cpu)
-   setup_pageset(_cpu(boot_pageset, cpu));
+   pageset_init(_cpu(boot_pageset, cpu));
 
 	mminit_verify_zonelist();

cpuset_init_current_mems_allowed();
@@ -6210,12 +6210,15 @@ static void pageset_init(struct per_cpu_pageset *p)
pcp = >pcp;
for (migratetype = 0; migratetype < MIGRATE_PCPTYPES; migratetype++)
INIT_LIST_HEAD(>lists[migratetype]);
-}
 
-static void setup_pageset(struct per_cpu_pageset *p)

-{
-   pageset_init(p);
-   pageset_update(>pcp, 0, 1);
+   /*
+* Set batch and high values safe for a boot pageset. A true percpu
+* pageset's initialization will update them subsequently. Here we don't
+* need to be as careful as pageset_update() as nobody can access the
+* pageset yet.


Isn't this slightly misleading? pageset_init is called from setup_zone_pageset
which is called from the memory hotplug as well. Isn't this more about


It is.


early zone initialization rather than boot pagesets? Or am I misreading
the patch?


It's for boot pagesets (call from build_all_zonelists_init()) that we need these 
particular values (well, just high = 0). For early zone initialization during 
hotplug the values don't matter as the caller is setup_zone_pageset() who 
immediately replaces the values by zone_set_pageset_high_and_batch(). Which is 
what the comment tries to say.



+*/
+   pcp->high = 0;
+   pcp->batch = 1;
 }
 
 /*

--
2.28.0

Re: [PATCH 3/9] mm, page_alloc: remove setup_pageset()

[Michal Hocko]

On Tue 22-09-20 16:37:06, Vlastimil Babka wrote:
> We initialize boot-time pagesets with setup_pageset(), which sets high and
> batch values that effectively disable pcplists.
> 
> We can remove this wrapper if we just set these values for all pagesets in
> pageset_init(). Non-boot pagesets then subsequently update them to the proper
> values.
> 
> No functional change.
> 
> Signed-off-by: Vlastimil Babka 
> ---
>  mm/page_alloc.c | 17 ++---
>  1 file changed, 10 insertions(+), 7 deletions(-)
> 
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index 26069c8d1b19..76c2b4578723 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -5823,7 +5823,7 @@ static void build_zonelists(pg_data_t *pgdat)
>   * not check if the processor is online before following the pageset pointer.
>   * Other parts of the kernel may not check if the zone is available.
>   */
> -static void setup_pageset(struct per_cpu_pageset *p);
> +static void pageset_init(struct per_cpu_pageset *p);
>  static DEFINE_PER_CPU(struct per_cpu_pageset, boot_pageset);
>  static DEFINE_PER_CPU(struct per_cpu_nodestat, boot_nodestats);
>  
> @@ -5891,7 +5891,7 @@ build_all_zonelists_init(void)
>* (a chicken-egg dilemma).
>*/
>   for_each_possible_cpu(cpu)
> - setup_pageset(_cpu(boot_pageset, cpu));
> + pageset_init(_cpu(boot_pageset, cpu));
>  
>   mminit_verify_zonelist();
>   cpuset_init_current_mems_allowed();
> @@ -6210,12 +6210,15 @@ static void pageset_init(struct per_cpu_pageset *p)
>   pcp = >pcp;
>   for (migratetype = 0; migratetype < MIGRATE_PCPTYPES; migratetype++)
>   INIT_LIST_HEAD(>lists[migratetype]);
> -}
>  
> -static void setup_pageset(struct per_cpu_pageset *p)
> -{
> - pageset_init(p);
> - pageset_update(>pcp, 0, 1);
> + /*
> +  * Set batch and high values safe for a boot pageset. A true percpu
> +  * pageset's initialization will update them subsequently. Here we don't
> +  * need to be as careful as pageset_update() as nobody can access the
> +  * pageset yet.

Isn't this slightly misleading? pageset_init is called from setup_zone_pageset
which is called from the memory hotplug as well. Isn't this more about
early zone initialization rather than boot pagesets? Or am I misreading
the patch?

> +  */
> + pcp->high = 0;
> + pcp->batch = 1;
>  }
>  
>  /*
> -- 
> 2.28.0

-- 
Michal Hocko
SUSE Labs

Re: [PATCH 3/9] mm, page_alloc: remove setup_pageset()

[David Hildenbrand]

On 22.09.20 16:37, Vlastimil Babka wrote:
> We initialize boot-time pagesets with setup_pageset(), which sets high and
> batch values that effectively disable pcplists.
> 
> We can remove this wrapper if we just set these values for all pagesets in
> pageset_init(). Non-boot pagesets then subsequently update them to the proper
> values.
> 
> No functional change.
> 
> Signed-off-by: Vlastimil Babka 
> ---
>  mm/page_alloc.c | 17 ++---
>  1 file changed, 10 insertions(+), 7 deletions(-)
> 
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index 26069c8d1b19..76c2b4578723 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -5823,7 +5823,7 @@ static void build_zonelists(pg_data_t *pgdat)
>   * not check if the processor is online before following the pageset pointer.
>   * Other parts of the kernel may not check if the zone is available.
>   */
> -static void setup_pageset(struct per_cpu_pageset *p);
> +static void pageset_init(struct per_cpu_pageset *p);
>  static DEFINE_PER_CPU(struct per_cpu_pageset, boot_pageset);
>  static DEFINE_PER_CPU(struct per_cpu_nodestat, boot_nodestats);
>  
> @@ -5891,7 +5891,7 @@ build_all_zonelists_init(void)
>* (a chicken-egg dilemma).
>*/
>   for_each_possible_cpu(cpu)
> - setup_pageset(_cpu(boot_pageset, cpu));
> + pageset_init(_cpu(boot_pageset, cpu));
>  
>   mminit_verify_zonelist();
>   cpuset_init_current_mems_allowed();
> @@ -6210,12 +6210,15 @@ static void pageset_init(struct per_cpu_pageset *p)
>   pcp = >pcp;
>   for (migratetype = 0; migratetype < MIGRATE_PCPTYPES; migratetype++)
>   INIT_LIST_HEAD(>lists[migratetype]);
> -}
>  
> -static void setup_pageset(struct per_cpu_pageset *p)
> -{
> - pageset_init(p);
> - pageset_update(>pcp, 0, 1);
> + /*
> +  * Set batch and high values safe for a boot pageset. A true percpu
> +  * pageset's initialization will update them subsequently. Here we don't
> +  * need to be as careful as pageset_update() as nobody can access the
> +  * pageset yet.
> +  */
> + pcp->high = 0;
> + pcp->batch = 1;
>  }
>  
>  /*
> 

Reviewed-by: David Hildenbrand 

-- 
Thanks,

David / dhildenb