[PATCH] mm: memcontrol: fix order calculation in try_charge()

[PATCH] mm: memcontrol: fix order calculation in try_charge()

[Jerome Marchand]

Since commit <6539cc05386> (mm: memcontrol: fold mem_cgroup_do_charge()),
the order to pass to mem_cgroup_oom() is calculated by passing the number
of pages to get_order() instead of the expected  size in bytes. AFAICT,
it only affects the value displayed in the oom warning message.
This patch fix this.

Signed-off-by: Jerome Marchand <jmarchan@redhat.com>
---
 mm/memcontrol.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 1742a2d..91bf094 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -2032,7 +2032,8 @@ retry:
 
 	mem_cgroup_events(mem_over_limit, MEMCG_OOM, 1);
 
-	mem_cgroup_oom(mem_over_limit, gfp_mask, get_order(nr_pages));
+	mem_cgroup_oom(mem_over_limit, gfp_mask,
+		       get_order(nr_pages * PAGE_SIZE));
 nomem:
 	if (!(gfp_mask & __GFP_NOFAIL))
 		return -ENOMEM;
-- 
1.9.3

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Re: [PATCH] mm: memcontrol: fix order calculation in try_charge()

[Michal Hocko]

On Tue 15-09-15 14:05:57, Jerome Marchand wrote:
> Since commit <6539cc05386> (mm: memcontrol: fold mem_cgroup_do_charge()),
> the order to pass to mem_cgroup_oom() is calculated by passing the number
> of pages to get_order() instead of the expected  size in bytes. AFAICT,
> it only affects the value displayed in the oom warning message.
> This patch fix this.

We haven't noticed that just because the OOM is enabled only for page
faults of order-0 (single page) and get_order work just fine. Thanks for
noticing this. If we ever start triggering OOM on different orders this
would be broken.
 
> Signed-off-by: Jerome Marchand <jmarchan@redhat.com>

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

Btw. a quick git grep shows that at least gart_iommu_init is using
number of pages as well. I haven't checked it does that intentionally,
though.

Thanks!

> ---
>  mm/memcontrol.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> index 1742a2d..91bf094 100644
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -2032,7 +2032,8 @@ retry:
>  
>  	mem_cgroup_events(mem_over_limit, MEMCG_OOM, 1);
>  
> -	mem_cgroup_oom(mem_over_limit, gfp_mask, get_order(nr_pages));
> +	mem_cgroup_oom(mem_over_limit, gfp_mask,
> +		       get_order(nr_pages * PAGE_SIZE));
>  nomem:
>  	if (!(gfp_mask & __GFP_NOFAIL))
>  		return -ENOMEM;
> -- 
> 1.9.3

-- 
Michal Hocko
SUSE Labs

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Re: [PATCH] mm: memcontrol: fix order calculation in try_charge()

[Michal Hocko]

[CC Andrew - the patch was posted here
http://lkml.kernel.org/r/1442318757-7141-1-git-send-email-jmarchan%40redhat.com]

On Tue 15-09-15 15:56:23, Michal Hocko wrote:
> On Tue 15-09-15 14:05:57, Jerome Marchand wrote:
> > Since commit <6539cc05386> (mm: memcontrol: fold mem_cgroup_do_charge()),
> > the order to pass to mem_cgroup_oom() is calculated by passing the number
> > of pages to get_order() instead of the expected  size in bytes. AFAICT,
> > it only affects the value displayed in the oom warning message.
> > This patch fix this.
> 
> We haven't noticed that just because the OOM is enabled only for page
> faults of order-0 (single page) and get_order work just fine. Thanks for
> noticing this. If we ever start triggering OOM on different orders this
> would be broken.
>  
> > Signed-off-by: Jerome Marchand <jmarchan@redhat.com>
> 
> Acked-by: Michal Hocko <mhocko@suse.com>
> 
> Btw. a quick git grep shows that at least gart_iommu_init is using
> number of pages as well. I haven't checked it does that intentionally,
> though.
> 
> Thanks!
> 
> > ---
> >  mm/memcontrol.c | 3 ++-
> >  1 file changed, 2 insertions(+), 1 deletion(-)
> > 
> > diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> > index 1742a2d..91bf094 100644
> > --- a/mm/memcontrol.c
> > +++ b/mm/memcontrol.c
> > @@ -2032,7 +2032,8 @@ retry:
> >  
> >  	mem_cgroup_events(mem_over_limit, MEMCG_OOM, 1);
> >  
> > -	mem_cgroup_oom(mem_over_limit, gfp_mask, get_order(nr_pages));
> > +	mem_cgroup_oom(mem_over_limit, gfp_mask,
> > +		       get_order(nr_pages * PAGE_SIZE));
> >  nomem:
> >  	if (!(gfp_mask & __GFP_NOFAIL))
> >  		return -ENOMEM;
> > -- 
> > 1.9.3
> 
> -- 
> Michal Hocko
> SUSE Labs

-- 
Michal Hocko
SUSE Labs

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Re: [PATCH] mm: memcontrol: fix order calculation in try_charge()

[Johannes Weiner]

On Tue, Sep 15, 2015 at 02:05:57PM +0200, Jerome Marchand wrote:
> Since commit <6539cc05386> (mm: memcontrol: fold mem_cgroup_do_charge()),
> the order to pass to mem_cgroup_oom() is calculated by passing the number
> of pages to get_order() instead of the expected  size in bytes. AFAICT,
> it only affects the value displayed in the oom warning message.
> This patch fix this.
> 
> Signed-off-by: Jerome Marchand <jmarchan@redhat.com>

Acked-by: Johannes Weiner <hannes@cmpxchg.org>

Thanks, Jerome. One minor thing:

> @@ -2032,7 +2032,8 @@ retry:
>  
>  	mem_cgroup_events(mem_over_limit, MEMCG_OOM, 1);
>  
> -	mem_cgroup_oom(mem_over_limit, gfp_mask, get_order(nr_pages));
> +	mem_cgroup_oom(mem_over_limit, gfp_mask,
> +		       get_order(nr_pages * PAGE_SIZE));

fls(nr_pages)?

get_order() is basically fls(x / PAGE_SIZE).

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