diff mbox series

[v5,04/11] mm: vmscan: remove memcg_shrinker_map_size

Message ID 20210127233345.339910-5-shy828301@gmail.com (mailing list archive)
State New
Headers show
Series Make shrinker's nr_deferred memcg aware | expand

Commit Message

Yang Shi Jan. 27, 2021, 11:33 p.m. UTC
Both memcg_shrinker_map_size and shrinker_nr_max is maintained, but actually the
map size can be calculated via shrinker_nr_max, so it seems unnecessary to keep both.
Remove memcg_shrinker_map_size since shrinker_nr_max is also used by iterating the
bit map.

Signed-off-by: Yang Shi <shy828301@gmail.com>
---
 mm/vmscan.c | 18 ++++++++----------
 1 file changed, 8 insertions(+), 10 deletions(-)

Comments

Vlastimil Babka Jan. 28, 2021, 4:53 p.m. UTC | #1
On 1/28/21 12:33 AM, Yang Shi wrote:
> Both memcg_shrinker_map_size and shrinker_nr_max is maintained, but actually the
> map size can be calculated via shrinker_nr_max, so it seems unnecessary to keep both.
> Remove memcg_shrinker_map_size since shrinker_nr_max is also used by iterating the
> bit map.
> 
> Signed-off-by: Yang Shi <shy828301@gmail.com>
> ---
>  mm/vmscan.c | 18 ++++++++----------
>  1 file changed, 8 insertions(+), 10 deletions(-)
> 
> diff --git a/mm/vmscan.c b/mm/vmscan.c
> index d3f3701dfcd2..847369c19775 100644
> --- a/mm/vmscan.c
> +++ b/mm/vmscan.c
> @@ -185,8 +185,7 @@ static LIST_HEAD(shrinker_list);
>  static DECLARE_RWSEM(shrinker_rwsem);
>  
>  #ifdef CONFIG_MEMCG
> -
> -static int memcg_shrinker_map_size;
> +static int shrinker_nr_max;
>  
>  static void free_shrinker_map_rcu(struct rcu_head *head)
>  {
> @@ -248,7 +247,7 @@ int alloc_shrinker_maps(struct mem_cgroup *memcg)
>  		return 0;
>  
>  	down_write(&shrinker_rwsem);
> -	size = memcg_shrinker_map_size;
> +	size = (shrinker_nr_max / BITS_PER_LONG + 1) * sizeof(unsigned long);
>  	for_each_node(nid) {
>  		map = kvzalloc_node(sizeof(*map) + size, GFP_KERNEL, nid);
>  		if (!map) {
> @@ -266,12 +265,13 @@ int alloc_shrinker_maps(struct mem_cgroup *memcg)
>  static int expand_shrinker_maps(int new_id)
>  {
>  	int size, old_size, ret = 0;
> +	int new_nr_max = new_id + 1;
>  	struct mem_cgroup *memcg;
>  
> -	size = DIV_ROUND_UP(new_id + 1, BITS_PER_LONG) * sizeof(unsigned long);
> -	old_size = memcg_shrinker_map_size;
> +	size = (new_nr_max / BITS_PER_LONG + 1) * sizeof(unsigned long);
> +	old_size = (shrinker_nr_max / BITS_PER_LONG + 1) * sizeof(unsigned long);

What's wrong with using DIV_ROUND_UP() here?

>  	if (size <= old_size)
> -		return 0;
> +		goto out;

Can this even happen? Seems to me it can't, so just remove this?

>  
>  	if (!root_mem_cgroup)
>  		goto out;
> @@ -286,9 +286,10 @@ static int expand_shrinker_maps(int new_id)
>  			goto out;
>  		}
>  	} while ((memcg = mem_cgroup_iter(NULL, memcg, NULL)) != NULL);
> +
>  out:
>  	if (!ret)
> -		memcg_shrinker_map_size = size;
> +		shrinker_nr_max = new_nr_max;
>  
>  	return ret;
>  }
> @@ -321,7 +322,6 @@ void set_shrinker_bit(struct mem_cgroup *memcg, int nid, int shrinker_id)
>  #define SHRINKER_REGISTERING ((struct shrinker *)~0UL)
>  
>  static DEFINE_IDR(shrinker_idr);
> -static int shrinker_nr_max;
>  
>  static int prealloc_memcg_shrinker(struct shrinker *shrinker)
>  {
> @@ -338,8 +338,6 @@ static int prealloc_memcg_shrinker(struct shrinker *shrinker)
>  			idr_remove(&shrinker_idr, id);
>  			goto unlock;
>  		}
> -
> -		shrinker_nr_max = id + 1;
>  	}
>  	shrinker->id = id;
>  	ret = 0;
>
Yang Shi Jan. 28, 2021, 9:22 p.m. UTC | #2
On Thu, Jan 28, 2021 at 8:53 AM Vlastimil Babka <vbabka@suse.cz> wrote:
>
> On 1/28/21 12:33 AM, Yang Shi wrote:
> > Both memcg_shrinker_map_size and shrinker_nr_max is maintained, but actually the
> > map size can be calculated via shrinker_nr_max, so it seems unnecessary to keep both.
> > Remove memcg_shrinker_map_size since shrinker_nr_max is also used by iterating the
> > bit map.
> >
> > Signed-off-by: Yang Shi <shy828301@gmail.com>
> > ---
> >  mm/vmscan.c | 18 ++++++++----------
> >  1 file changed, 8 insertions(+), 10 deletions(-)
> >
> > diff --git a/mm/vmscan.c b/mm/vmscan.c
> > index d3f3701dfcd2..847369c19775 100644
> > --- a/mm/vmscan.c
> > +++ b/mm/vmscan.c
> > @@ -185,8 +185,7 @@ static LIST_HEAD(shrinker_list);
> >  static DECLARE_RWSEM(shrinker_rwsem);
> >
> >  #ifdef CONFIG_MEMCG
> > -
> > -static int memcg_shrinker_map_size;
> > +static int shrinker_nr_max;
> >
> >  static void free_shrinker_map_rcu(struct rcu_head *head)
> >  {
> > @@ -248,7 +247,7 @@ int alloc_shrinker_maps(struct mem_cgroup *memcg)
> >               return 0;
> >
> >       down_write(&shrinker_rwsem);
> > -     size = memcg_shrinker_map_size;
> > +     size = (shrinker_nr_max / BITS_PER_LONG + 1) * sizeof(unsigned long);
> >       for_each_node(nid) {
> >               map = kvzalloc_node(sizeof(*map) + size, GFP_KERNEL, nid);
> >               if (!map) {
> > @@ -266,12 +265,13 @@ int alloc_shrinker_maps(struct mem_cgroup *memcg)
> >  static int expand_shrinker_maps(int new_id)
> >  {
> >       int size, old_size, ret = 0;
> > +     int new_nr_max = new_id + 1;
> >       struct mem_cgroup *memcg;
> >
> > -     size = DIV_ROUND_UP(new_id + 1, BITS_PER_LONG) * sizeof(unsigned long);
> > -     old_size = memcg_shrinker_map_size;
> > +     size = (new_nr_max / BITS_PER_LONG + 1) * sizeof(unsigned long);
> > +     old_size = (shrinker_nr_max / BITS_PER_LONG + 1) * sizeof(unsigned long);
>
> What's wrong with using DIV_ROUND_UP() here?

I don't think there is anything wrong with DIV_ROUND_UP. Should be
just different taste and result in shorter statement.

>
> >       if (size <= old_size)
> > -             return 0;
> > +             goto out;
>
> Can this even happen? Seems to me it can't, so just remove this?

Yes, it can. The maps use unsigned long value for bitmap, so any
shrinker ID < 31 would fall into the same unsigned long, so we may see
size <= old_size, but we need increase shrinker_nr_max since
expand_shrinker_maps() is called iff id >= shrinker_nr_max.

>
> >
> >       if (!root_mem_cgroup)
> >               goto out;
> > @@ -286,9 +286,10 @@ static int expand_shrinker_maps(int new_id)
> >                       goto out;
> >               }
> >       } while ((memcg = mem_cgroup_iter(NULL, memcg, NULL)) != NULL);
> > +
> >  out:
> >       if (!ret)
> > -             memcg_shrinker_map_size = size;
> > +             shrinker_nr_max = new_nr_max;
> >
> >       return ret;
> >  }
> > @@ -321,7 +322,6 @@ void set_shrinker_bit(struct mem_cgroup *memcg, int nid, int shrinker_id)
> >  #define SHRINKER_REGISTERING ((struct shrinker *)~0UL)
> >
> >  static DEFINE_IDR(shrinker_idr);
> > -static int shrinker_nr_max;
> >
> >  static int prealloc_memcg_shrinker(struct shrinker *shrinker)
> >  {
> > @@ -338,8 +338,6 @@ static int prealloc_memcg_shrinker(struct shrinker *shrinker)
> >                       idr_remove(&shrinker_idr, id);
> >                       goto unlock;
> >               }
> > -
> > -             shrinker_nr_max = id + 1;
> >       }
> >       shrinker->id = id;
> >       ret = 0;
> >
>
Vlastimil Babka Jan. 29, 2021, 11:22 a.m. UTC | #3
On 1/28/21 10:22 PM, Yang Shi wrote:
>> > @@ -266,12 +265,13 @@ int alloc_shrinker_maps(struct mem_cgroup *memcg)
>> >  static int expand_shrinker_maps(int new_id)
>> >  {
>> >       int size, old_size, ret = 0;
>> > +     int new_nr_max = new_id + 1;
>> >       struct mem_cgroup *memcg;
>> >
>> > -     size = DIV_ROUND_UP(new_id + 1, BITS_PER_LONG) * sizeof(unsigned long);
>> > -     old_size = memcg_shrinker_map_size;
>> > +     size = (new_nr_max / BITS_PER_LONG + 1) * sizeof(unsigned long);
>> > +     old_size = (shrinker_nr_max / BITS_PER_LONG + 1) * sizeof(unsigned long);
>>
>> What's wrong with using DIV_ROUND_UP() here?
> 
> I don't think there is anything wrong with DIV_ROUND_UP. Should be
> just different taste and result in shorter statement.

IMHO it's not just taste. DIV_ROUND_UP() says what it does and you don't need to
guess it from the math expression. Also your expression is shorter as it simply
adds + 1, so if shrinker_nr_max is a multiple of BITS_PER_LONG, there's an extra
unsigned long that shouldn't be needed. People reading that code will wonder
whether there was some non-obvious intention behind that, and possibly send
cleanup patches.

>>
>> >       if (size <= old_size)
>> > -             return 0;
>> > +             goto out;
>>
>> Can this even happen? Seems to me it can't, so just remove this?
> 
> Yes, it can. The maps use unsigned long value for bitmap, so any
> shrinker ID < 31 would fall into the same unsigned long, so we may see
> size <= old_size, but we need increase shrinker_nr_max since
> expand_shrinker_maps() is called iff id >= shrinker_nr_max.

Ah, good point.
Yang Shi Jan. 29, 2021, 5:05 p.m. UTC | #4
On Fri, Jan 29, 2021 at 3:22 AM Vlastimil Babka <vbabka@suse.cz> wrote:
>
> On 1/28/21 10:22 PM, Yang Shi wrote:
> >> > @@ -266,12 +265,13 @@ int alloc_shrinker_maps(struct mem_cgroup *memcg)
> >> >  static int expand_shrinker_maps(int new_id)
> >> >  {
> >> >       int size, old_size, ret = 0;
> >> > +     int new_nr_max = new_id + 1;
> >> >       struct mem_cgroup *memcg;
> >> >
> >> > -     size = DIV_ROUND_UP(new_id + 1, BITS_PER_LONG) * sizeof(unsigned long);
> >> > -     old_size = memcg_shrinker_map_size;
> >> > +     size = (new_nr_max / BITS_PER_LONG + 1) * sizeof(unsigned long);
> >> > +     old_size = (shrinker_nr_max / BITS_PER_LONG + 1) * sizeof(unsigned long);
> >>
> >> What's wrong with using DIV_ROUND_UP() here?
> >
> > I don't think there is anything wrong with DIV_ROUND_UP. Should be
> > just different taste and result in shorter statement.
>
> IMHO it's not just taste. DIV_ROUND_UP() says what it does and you don't need to
> guess it from the math expression. Also your expression is shorter as it simply
> adds + 1, so if shrinker_nr_max is a multiple of BITS_PER_LONG, there's an extra
> unsigned long that shouldn't be needed. People reading that code will wonder
> whether there was some non-obvious intention behind that, and possibly send
> cleanup patches.

OK, will replace back to DIV_ROUND_UP(). And, a helper macro is
introduced in patch #6, will add that helper in this patch and use
DIV_ROUND_UP() in the helper.

>
> >>
> >> >       if (size <= old_size)
> >> > -             return 0;
> >> > +             goto out;
> >>
> >> Can this even happen? Seems to me it can't, so just remove this?
> >
> > Yes, it can. The maps use unsigned long value for bitmap, so any
> > shrinker ID < 31 would fall into the same unsigned long, so we may see
> > size <= old_size, but we need increase shrinker_nr_max since
> > expand_shrinker_maps() is called iff id >= shrinker_nr_max.
>
> Ah, good point.
diff mbox series

Patch

diff --git a/mm/vmscan.c b/mm/vmscan.c
index d3f3701dfcd2..847369c19775 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -185,8 +185,7 @@  static LIST_HEAD(shrinker_list);
 static DECLARE_RWSEM(shrinker_rwsem);
 
 #ifdef CONFIG_MEMCG
-
-static int memcg_shrinker_map_size;
+static int shrinker_nr_max;
 
 static void free_shrinker_map_rcu(struct rcu_head *head)
 {
@@ -248,7 +247,7 @@  int alloc_shrinker_maps(struct mem_cgroup *memcg)
 		return 0;
 
 	down_write(&shrinker_rwsem);
-	size = memcg_shrinker_map_size;
+	size = (shrinker_nr_max / BITS_PER_LONG + 1) * sizeof(unsigned long);
 	for_each_node(nid) {
 		map = kvzalloc_node(sizeof(*map) + size, GFP_KERNEL, nid);
 		if (!map) {
@@ -266,12 +265,13 @@  int alloc_shrinker_maps(struct mem_cgroup *memcg)
 static int expand_shrinker_maps(int new_id)
 {
 	int size, old_size, ret = 0;
+	int new_nr_max = new_id + 1;
 	struct mem_cgroup *memcg;
 
-	size = DIV_ROUND_UP(new_id + 1, BITS_PER_LONG) * sizeof(unsigned long);
-	old_size = memcg_shrinker_map_size;
+	size = (new_nr_max / BITS_PER_LONG + 1) * sizeof(unsigned long);
+	old_size = (shrinker_nr_max / BITS_PER_LONG + 1) * sizeof(unsigned long);
 	if (size <= old_size)
-		return 0;
+		goto out;
 
 	if (!root_mem_cgroup)
 		goto out;
@@ -286,9 +286,10 @@  static int expand_shrinker_maps(int new_id)
 			goto out;
 		}
 	} while ((memcg = mem_cgroup_iter(NULL, memcg, NULL)) != NULL);
+
 out:
 	if (!ret)
-		memcg_shrinker_map_size = size;
+		shrinker_nr_max = new_nr_max;
 
 	return ret;
 }
@@ -321,7 +322,6 @@  void set_shrinker_bit(struct mem_cgroup *memcg, int nid, int shrinker_id)
 #define SHRINKER_REGISTERING ((struct shrinker *)~0UL)
 
 static DEFINE_IDR(shrinker_idr);
-static int shrinker_nr_max;
 
 static int prealloc_memcg_shrinker(struct shrinker *shrinker)
 {
@@ -338,8 +338,6 @@  static int prealloc_memcg_shrinker(struct shrinker *shrinker)
 			idr_remove(&shrinker_idr, id);
 			goto unlock;
 		}
-
-		shrinker_nr_max = id + 1;
 	}
 	shrinker->id = id;
 	ret = 0;