Re: [ 39/40] cpuset: mm: reduce large amounts of memory barrier related damage v3

[Herton Ronaldo Krzesinski]

On Fri, Jul 27, 2012 at 12:01:16PM -0700, Greg Kroah-Hartman wrote:
> On Fri, Jul 27, 2012 at 04:23:47PM +0100, Mel Gorman wrote:
> > > > --- a/mm/slub.c
> > > > +++ b/mm/slub.c
> > > > @@ -1457,6 +1457,7 @@ static struct page *get_any_partial(stru
> > > >         struct zone *zone;
> > > >         enum zone_type high_zoneidx = gfp_zone(flags);
> > > >         struct page *page;
> > > > +       unsigned int cpuset_mems_cookie;
> > > >  
> > > >         /*
> > > >          * The defrag ratio allows a configuration of the tradeoffs 
> > > > between
> > > > @@ -1480,22 +1481,32 @@ static struct page *get_any_partial(stru
> > > >                         get_cycles() % 1024 > 
> > > > s->remote_node_defrag_ratio)
> > > >                 return NULL;
> > > >  
> > > > -       get_mems_allowed();
> > > > -       zonelist = node_zonelist(slab_node(current->mempolicy), flags);
> > > > -       for_each_zone_zonelist(zone, z, zonelist, high_zoneidx) {
> > > > -               struct kmem_cache_node *n;
> > > > +       do {
> > > > +               cpuset_mems_cookie = get_mems_allowed();
> > > > +               zonelist = node_zonelist(slab_node(current->mempolicy), 
> > > > flags);
> > > > +               for_each_zone_zonelist(zone, z, zonelist, high_zoneidx) 
> > > > {
> > > > +                       struct kmem_cache_node *n;
> > > >  
> > > > -               n = get_node(s, zone_to_nid(zone));
> > > > +                       n = get_node(s, zone_to_nid(zone));
> > > >  
> > > > -               if (n && cpuset_zone_allowed_hardwall(zone, flags) &&
> > > > -                               n->nr_partial > s->min_partial) {
> > > > -                       page = get_partial_node(n);
> > > > -                       if (page) {
> > > > -                               put_mems_allowed();
> > > > -                               return page;
> > > > +                       if (n && cpuset_zone_allowed_hardwall(zone, 
> > > > flags) &&
> > > > +                                       n->nr_partial > s->min_partial) 
> > > > {
> > > > +                               page = get_partial_node(n);
> > > > +                               if (page) {
> > > > +                                       /*
> > > > +                                        * Return the object even if
> > > > +                                        * put_mems_allowed indicated 
> > > > that
> > > > +                                        * the cpuset mems_allowed was
> > > > +                                        * updated in parallel. It's a
> > > > +                                        * harmless race between the 
> > > > alloc
> > > > +                                        * and the cpuset update.
> > > > +                                        */
> > > > +                                       
> > > > put_mems_allowed(cpuset_mems_cookie);
> > > > +                                       return page;
> > > > +                               }
> > > >                         }
> > > >                 }
> > > > -       }
> > > > +       } while (!put_mems_allowed(cpuset_mems_cookie));
> > > >         put_mems_allowed();
> > > 
> > > This doesn't build on 3.0, the backport left the stray put_mems_allowed
> > > above:
> > > 
> > > linux-stable/mm/slub.c: In function 'get_any_partial':
> > > linux-stable/mm/slub.c:1510:2: error: too few arguments to function 
> > > 'put_mems_allowed'
> > > linux-stable/include/linux/cpuset.h:108:20: note: declared here
> > > 
> > 
> > That line should have been deleted and tests were based on slab. My
> > apologies.
> > 
> > ---8<---
> > cpuset: mm: Reduce large amounts of memory barrier related damage fix
> > 
> > linux-stable/mm/slub.c: In function 'get_any_partial':
> > linux-stable/mm/slub.c:1510:2: error: too few arguments to function 
> > 'put_mems_allowed'
> > linux-stable/include/linux/cpuset.h:108:20: note: declared here
> > 
> > Reported-by: Herton Ronaldo Krzesinski <herton.krzesin...@canonical.com>
> > Signed-off-by: Mel Gorman <mgor...@suse.de>
> > 
> > diff --git a/mm/slub.c b/mm/slub.c
> > index 00ccf2c..ae6e80e 100644
> > --- a/mm/slub.c
> > +++ b/mm/slub.c
> > @@ -1507,7 +1507,6 @@ static struct page *get_any_partial(struct kmem_cache 
> > *s, gfp_t flags)
> >                     }
> >             }
> >     } while (!put_mems_allowed(cpuset_mems_cookie));
> > -   put_mems_allowed();
> >  #endif
> >     return NULL;
> >  }
> 
> Thanks, I've merged this with the "original" in the tree, so all should
> be good now.

Thanks. I saw what seems another issue now on the patch too, sorry for
not noticing earlier: this backport is lacking the
write_seqcount_{begin,end} on set_mems_allowed for the case with
CONFIG_CPUSETS, like in the original patch:

 static inline void set_mems_allowed(nodemask_t nodemask)
 {
        task_lock(current);
+       write_seqcount_begin(&current->mems_allowed_seq);
        current->mems_allowed = nodemask;
+       write_seqcount_end(&current->mems_allowed_seq);
        task_unlock(current);
 }



> 
> greg k-h
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