2020-09-14 02:46:29

by Waiman Long

Subject: [PATCH v2 2/3] mm/memcg: Simplify mem_cgroup_get_max()

The mem_cgroup_get_max() function used to get memory+swap max from
both the v1 memsw and v2 memory+swap page counters & return the maximum
of these 2 values. This is redundant and it is more efficient to just
get either the v1 or the v2 values depending on which one is currently
in use.

Signed-off-by: Waiman Long <[email protected]>
---
mm/memcontrol.c | 20 +++++++++-----------
1 file changed, 9 insertions(+), 11 deletions(-)

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 8c74f1200261..ca36bed588d1 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -1633,17 +1633,15 @@ void mem_cgroup_print_oom_meminfo(struct mem_cgroup *memcg)
*/
unsigned long mem_cgroup_get_max(struct mem_cgroup *memcg)
{
- unsigned long max;
-
- max = READ_ONCE(memcg->memory.max);
- if (mem_cgroup_swappiness(memcg)) {
- unsigned long memsw_max;
- unsigned long swap_max;
-
- memsw_max = memcg->memsw.max;
- swap_max = READ_ONCE(memcg->swap.max);
- swap_max = min(swap_max, (unsigned long)total_swap_pages);
- max = min(max + swap_max, memsw_max);
+ unsigned long max = READ_ONCE(memcg->memory.max);
+
+ if (cgroup_subsys_on_dfl(memory_cgrp_subsys)) {
+ if (mem_cgroup_swappiness(memcg))
+ max += min(READ_ONCE(memcg->swap.max),
+ (unsigned long)total_swap_pages);
+ } else { /* v1 */
+ if (mem_cgroup_swappiness(memcg))
+ max = memcg->memsw.max;
}
return max;
}
--
2.18.1

2020-09-14 11:59:03

by Michal Hocko

Subject: Re: [PATCH v2 2/3] mm/memcg: Simplify mem_cgroup_get_max()

On Sun 13-09-20 22:44:51, Waiman Long wrote:
> The mem_cgroup_get_max() function used to get memory+swap max from
> both the v1 memsw and v2 memory+swap page counters & return the maximum
> of these 2 values. This is redundant and it is more efficient to just
> get either the v1 or the v2 values depending on which one is currently
> in use.
>
> Signed-off-by: Waiman Long <[email protected]>
> ---
> mm/memcontrol.c | 20 +++++++++-----------
> 1 file changed, 9 insertions(+), 11 deletions(-)
>
> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> index 8c74f1200261..ca36bed588d1 100644
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -1633,17 +1633,15 @@ void mem_cgroup_print_oom_meminfo(struct mem_cgroup *memcg)
> */
> unsigned long mem_cgroup_get_max(struct mem_cgroup *memcg)
> {
> - unsigned long max;
> -
> - max = READ_ONCE(memcg->memory.max);
> - if (mem_cgroup_swappiness(memcg)) {
> - unsigned long memsw_max;
> - unsigned long swap_max;
> -
> - memsw_max = memcg->memsw.max;
> - swap_max = READ_ONCE(memcg->swap.max);
> - swap_max = min(swap_max, (unsigned long)total_swap_pages);
> - max = min(max + swap_max, memsw_max);
> + unsigned long max = READ_ONCE(memcg->memory.max);
> +
> + if (cgroup_subsys_on_dfl(memory_cgrp_subsys)) {
> + if (mem_cgroup_swappiness(memcg))
> + max += min(READ_ONCE(memcg->swap.max),
> + (unsigned long)total_swap_pages);
> + } else { /* v1 */
> + if (mem_cgroup_swappiness(memcg))
> + max = memcg->memsw.max;

I agree that making v1 vs. v2 distinction here makes the code more
obvious. But I do not think your code is correct for v1. In a default
state it would lead to max = PAGE_COUNTER_MAX which is not something
we want, right?

instead you want
max += min(READ_ONCE(memcg->memsw.max), total_swap_pages);



> }
> return max;
> }
> --
> 2.18.1
>

--
Michal Hocko
SUSE Labs

2020-09-14 14:02:03

by Waiman Long

Subject: Re: [PATCH v2 2/3] mm/memcg: Simplify mem_cgroup_get_max()

On 9/14/20 7:48 AM, Michal Hocko wrote:
> On Sun 13-09-20 22:44:51, Waiman Long wrote:
>> The mem_cgroup_get_max() function used to get memory+swap max from
>> both the v1 memsw and v2 memory+swap page counters & return the maximum
>> of these 2 values. This is redundant and it is more efficient to just
>> get either the v1 or the v2 values depending on which one is currently
>> in use.
>>
>> Signed-off-by: Waiman Long <[email protected]>
>> ---
>> mm/memcontrol.c | 20 +++++++++-----------
>> 1 file changed, 9 insertions(+), 11 deletions(-)
>>
>> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
>> index 8c74f1200261..ca36bed588d1 100644
>> --- a/mm/memcontrol.c
>> +++ b/mm/memcontrol.c
>> @@ -1633,17 +1633,15 @@ void mem_cgroup_print_oom_meminfo(struct mem_cgroup *memcg)
>> */
>> unsigned long mem_cgroup_get_max(struct mem_cgroup *memcg)
>> {
>> - unsigned long max;
>> -
>> - max = READ_ONCE(memcg->memory.max);
>> - if (mem_cgroup_swappiness(memcg)) {
>> - unsigned long memsw_max;
>> - unsigned long swap_max;
>> -
>> - memsw_max = memcg->memsw.max;
>> - swap_max = READ_ONCE(memcg->swap.max);
>> - swap_max = min(swap_max, (unsigned long)total_swap_pages);
>> - max = min(max + swap_max, memsw_max);
>> + unsigned long max = READ_ONCE(memcg->memory.max);
>> +
>> + if (cgroup_subsys_on_dfl(memory_cgrp_subsys)) {
>> + if (mem_cgroup_swappiness(memcg))
>> + max += min(READ_ONCE(memcg->swap.max),
>> + (unsigned long)total_swap_pages);
>> + } else { /* v1 */
>> + if (mem_cgroup_swappiness(memcg))
>> + max = memcg->memsw.max;
> I agree that making v1 vs. v2 distinction here makes the code more
> obvious. But I do not think your code is correct for v1. In a default
> state it would lead to max = PAGE_COUNTER_MAX which is not something
> we want, right?
>
> instead you want
> max += min(READ_ONCE(memcg->memsw.max), total_swap_pages);
>
You are right, it is a bit tricky for v1.

I will change it to

    max += min(READ_ONCE(memcg->memsw.max) - max, total_swap_pages):

Thanks,
Longman

2020-09-14 21:33:36

by Johannes Weiner

Subject: Re: [PATCH v2 2/3] mm/memcg: Simplify mem_cgroup_get_max()

On Mon, Sep 14, 2020 at 09:51:26AM -0400, Waiman Long wrote:
> On 9/14/20 7:48 AM, Michal Hocko wrote:
> > On Sun 13-09-20 22:44:51, Waiman Long wrote:
> > > The mem_cgroup_get_max() function used to get memory+swap max from
> > > both the v1 memsw and v2 memory+swap page counters & return the maximum
> > > of these 2 values. This is redundant and it is more efficient to just
> > > get either the v1 or the v2 values depending on which one is currently
> > > in use.
> > >
> > > Signed-off-by: Waiman Long <[email protected]>
> > > ---
> > > mm/memcontrol.c | 20 +++++++++-----------
> > > 1 file changed, 9 insertions(+), 11 deletions(-)
> > >
> > > diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> > > index 8c74f1200261..ca36bed588d1 100644
> > > --- a/mm/memcontrol.c
> > > +++ b/mm/memcontrol.c
> > > @@ -1633,17 +1633,15 @@ void mem_cgroup_print_oom_meminfo(struct mem_cgroup *memcg)
> > > */
> > > unsigned long mem_cgroup_get_max(struct mem_cgroup *memcg)
> > > {
> > > - unsigned long max;
> > > -
> > > - max = READ_ONCE(memcg->memory.max);
> > > - if (mem_cgroup_swappiness(memcg)) {
> > > - unsigned long memsw_max;
> > > - unsigned long swap_max;
> > > -
> > > - memsw_max = memcg->memsw.max;
> > > - swap_max = READ_ONCE(memcg->swap.max);
> > > - swap_max = min(swap_max, (unsigned long)total_swap_pages);
> > > - max = min(max + swap_max, memsw_max);
> > > + unsigned long max = READ_ONCE(memcg->memory.max);
> > > +
> > > + if (cgroup_subsys_on_dfl(memory_cgrp_subsys)) {
> > > + if (mem_cgroup_swappiness(memcg))
> > > + max += min(READ_ONCE(memcg->swap.max),
> > > + (unsigned long)total_swap_pages);
> > > + } else { /* v1 */
> > > + if (mem_cgroup_swappiness(memcg))
> > > + max = memcg->memsw.max;
> > I agree that making v1 vs. v2 distinction here makes the code more
> > obvious. But I do not think your code is correct for v1. In a default
> > state it would lead to max = PAGE_COUNTER_MAX which is not something
> > we want, right?
> >
> > instead you want
> > max += min(READ_ONCE(memcg->memsw.max), total_swap_pages);
> >
> You are right, it is a bit tricky for v1.
>
> I will change it to
>
> ??? max += min(READ_ONCE(memcg->memsw.max) - max, total_swap_pages):

memsw.max can be smaller than max.

max = min3(max, READ_ONCE(memcg->memsw.max), total_swap_pages)?

2020-09-14 21:37:35

by Johannes Weiner

Subject: Re: [PATCH v2 2/3] mm/memcg: Simplify mem_cgroup_get_max()

On Mon, Sep 14, 2020 at 05:29:06PM -0400, Johannes Weiner wrote:
> On Mon, Sep 14, 2020 at 09:51:26AM -0400, Waiman Long wrote:
> > On 9/14/20 7:48 AM, Michal Hocko wrote:
> > > On Sun 13-09-20 22:44:51, Waiman Long wrote:
> > > > The mem_cgroup_get_max() function used to get memory+swap max from
> > > > both the v1 memsw and v2 memory+swap page counters & return the maximum
> > > > of these 2 values. This is redundant and it is more efficient to just
> > > > get either the v1 or the v2 values depending on which one is currently
> > > > in use.
> > > >
> > > > Signed-off-by: Waiman Long <[email protected]>
> > > > ---
> > > > mm/memcontrol.c | 20 +++++++++-----------
> > > > 1 file changed, 9 insertions(+), 11 deletions(-)
> > > >
> > > > diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> > > > index 8c74f1200261..ca36bed588d1 100644
> > > > --- a/mm/memcontrol.c
> > > > +++ b/mm/memcontrol.c
> > > > @@ -1633,17 +1633,15 @@ void mem_cgroup_print_oom_meminfo(struct mem_cgroup *memcg)
> > > > */
> > > > unsigned long mem_cgroup_get_max(struct mem_cgroup *memcg)
> > > > {
> > > > - unsigned long max;
> > > > -
> > > > - max = READ_ONCE(memcg->memory.max);
> > > > - if (mem_cgroup_swappiness(memcg)) {
> > > > - unsigned long memsw_max;
> > > > - unsigned long swap_max;
> > > > -
> > > > - memsw_max = memcg->memsw.max;
> > > > - swap_max = READ_ONCE(memcg->swap.max);
> > > > - swap_max = min(swap_max, (unsigned long)total_swap_pages);
> > > > - max = min(max + swap_max, memsw_max);
> > > > + unsigned long max = READ_ONCE(memcg->memory.max);
> > > > +
> > > > + if (cgroup_subsys_on_dfl(memory_cgrp_subsys)) {
> > > > + if (mem_cgroup_swappiness(memcg))
> > > > + max += min(READ_ONCE(memcg->swap.max),
> > > > + (unsigned long)total_swap_pages);
> > > > + } else { /* v1 */
> > > > + if (mem_cgroup_swappiness(memcg))
> > > > + max = memcg->memsw.max;
> > > I agree that making v1 vs. v2 distinction here makes the code more
> > > obvious. But I do not think your code is correct for v1. In a default
> > > state it would lead to max = PAGE_COUNTER_MAX which is not something
> > > we want, right?
> > >
> > > instead you want
> > > max += min(READ_ONCE(memcg->memsw.max), total_swap_pages);
> > >
> > You are right, it is a bit tricky for v1.
> >
> > I will change it to
> >
> > ??? max += min(READ_ONCE(memcg->memsw.max) - max, total_swap_pages):
>
> memsw.max can be smaller than max.
>
> max = min3(max, READ_ONCE(memcg->memsw.max), total_swap_pages)?

Nevermind, I saw the follow-up below, and it's indeed not allowed to
configure it like that.