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Re: [PATCH] vmpressure: Fix subtree pressure detection

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  Re: [PATCH] vmpressure: Fix subtree pressure detection Michal Hocko <mhocko@kernel.org> - 2016-01-28 17:00 +0100
    Re: [PATCH] vmpressure: Fix subtree pressure detection Vlastimil Babka <vbabka@suse.cz> - 2016-01-28 20:30 +0100
      Re: [PATCH] vmpressure: Fix subtree pressure detection Vladimir Davydov <vdavydov@virtuozzo.com> - 2016-01-29 09:40 +0100
        Re: [PATCH] vmpressure: Fix subtree pressure detection Andrew Morton <akpm@linux-foundation.org> - 2016-02-02 07:30 +0100

#1320821 — Re: [PATCH] vmpressure: Fix subtree pressure detection

On Wed 27-01-16 19:28:57, Vladimir Davydov wrote:
> When vmpressure is called for the entire subtree under pressure we
> mistakenly use vmpressure->scanned instead of vmpressure->tree_scanned
> when checking if vmpressure work is to be scheduled. This results in
> suppressing all vmpressure events in the legacy cgroup hierarchy. Fix
> it.
> 
> Fixes: 8e8ae645249b ("mm: memcontrol: hook up vmpressure to socket pressure")
> Signed-off-by: Vladimir Davydov <vdavydov@virtuozzo.com>

a = b += c made me scratch my head for a second but this looks correct

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

> ---
>  mm/vmpressure.c | 3 +--
>  1 file changed, 1 insertion(+), 2 deletions(-)
> 
> diff --git a/mm/vmpressure.c b/mm/vmpressure.c
> index 9a6c0704211c..149fdf6c5c56 100644
> --- a/mm/vmpressure.c
> +++ b/mm/vmpressure.c
> @@ -248,9 +248,8 @@ void vmpressure(gfp_t gfp, struct mem_cgroup *memcg, bool tree,
>  
>  	if (tree) {
>  		spin_lock(&vmpr->sr_lock);
> -		vmpr->tree_scanned += scanned;
> +		scanned = vmpr->tree_scanned += scanned;
>  		vmpr->tree_reclaimed += reclaimed;
> -		scanned = vmpr->scanned;
>  		spin_unlock(&vmpr->sr_lock);
>  
>  		if (scanned < vmpressure_win)
> -- 
> 2.1.4

-- 
Michal Hocko
SUSE Labs

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#1320960

On 28.1.2016 16:55, Michal Hocko wrote:
> On Wed 27-01-16 19:28:57, Vladimir Davydov wrote:
>> When vmpressure is called for the entire subtree under pressure we
>> mistakenly use vmpressure->scanned instead of vmpressure->tree_scanned
>> when checking if vmpressure work is to be scheduled. This results in
>> suppressing all vmpressure events in the legacy cgroup hierarchy. Fix
>> it.
>>
>> Fixes: 8e8ae645249b ("mm: memcontrol: hook up vmpressure to socket pressure")
>> Signed-off-by: Vladimir Davydov <vdavydov@virtuozzo.com>
> 
> a = b += c made me scratch my head for a second but this looks correct

Ugh, it's actually a = b += a

While clever and compact, this will make scratch their head anyone looking at
the code in the future. Is it worth it?

> Acked-by: Michal Hocko <mhocko@suse.com>
> 
>> ---
>>  mm/vmpressure.c | 3 +--
>>  1 file changed, 1 insertion(+), 2 deletions(-)
>>
>> diff --git a/mm/vmpressure.c b/mm/vmpressure.c
>> index 9a6c0704211c..149fdf6c5c56 100644
>> --- a/mm/vmpressure.c
>> +++ b/mm/vmpressure.c
>> @@ -248,9 +248,8 @@ void vmpressure(gfp_t gfp, struct mem_cgroup *memcg, bool tree,
>>  
>>  	if (tree) {
>>  		spin_lock(&vmpr->sr_lock);
>> -		vmpr->tree_scanned += scanned;
>> +		scanned = vmpr->tree_scanned += scanned;
>>  		vmpr->tree_reclaimed += reclaimed;
>> -		scanned = vmpr->scanned;
>>  		spin_unlock(&vmpr->sr_lock);
>>  
>>  		if (scanned < vmpressure_win)
>> -- 
>> 2.1.4
> 

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#1321559

On Thu, Jan 28, 2016 at 08:24:30PM +0100, Vlastimil Babka wrote:
> On 28.1.2016 16:55, Michal Hocko wrote:
> > On Wed 27-01-16 19:28:57, Vladimir Davydov wrote:
> >> When vmpressure is called for the entire subtree under pressure we
> >> mistakenly use vmpressure->scanned instead of vmpressure->tree_scanned
> >> when checking if vmpressure work is to be scheduled. This results in
> >> suppressing all vmpressure events in the legacy cgroup hierarchy. Fix
> >> it.
> >>
> >> Fixes: 8e8ae645249b ("mm: memcontrol: hook up vmpressure to socket pressure")
> >> Signed-off-by: Vladimir Davydov <vdavydov@virtuozzo.com>
> > 
> > a = b += c made me scratch my head for a second but this looks correct
> 
> Ugh, it's actually a = b += a
> 
> While clever and compact, this will make scratch their head anyone looking at
> the code in the future. Is it worth it?

I'm just trying to be consistend with the !tree case, where we do
exactly the same.

Thanks,
Vladimir

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#1323823

On Fri, 29 Jan 2016 11:37:49 +0300 Vladimir Davydov <vdavydov@virtuozzo.com> wrote:

> On Thu, Jan 28, 2016 at 08:24:30PM +0100, Vlastimil Babka wrote:
> > On 28.1.2016 16:55, Michal Hocko wrote:
> > > On Wed 27-01-16 19:28:57, Vladimir Davydov wrote:
> > >> When vmpressure is called for the entire subtree under pressure we
> > >> mistakenly use vmpressure->scanned instead of vmpressure->tree_scanned
> > >> when checking if vmpressure work is to be scheduled. This results in
> > >> suppressing all vmpressure events in the legacy cgroup hierarchy. Fix
> > >> it.
> > >>
> > >> Fixes: 8e8ae645249b ("mm: memcontrol: hook up vmpressure to socket pressure")
> > >> Signed-off-by: Vladimir Davydov <vdavydov@virtuozzo.com>
> > > 
> > > a = b += c made me scratch my head for a second but this looks correct
> > 
> > Ugh, it's actually a = b += a
> > 
> > While clever and compact, this will make scratch their head anyone looking at
> > the code in the future. Is it worth it?
> 
> I'm just trying to be consistend with the !tree case, where we do
> exactly the same.

I stared suspiciously at it for a while, decided to let it go. 
Possibly we can remove local `scanned' altogether.  No matter, someone
will clean it all up sometime.

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