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

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Date:	Sat, 28 Jul 2012 02:02:31 -0300
From:	Herton Ronaldo Krzesinski <herton.krzesinski@...onical.com>
To:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:	Mel Gorman <mgorman@...e.de>, linux-kernel@...r.kernel.org,
	stable@...r.kernel.org, torvalds@...ux-foundation.org,
	akpm@...ux-foundation.org, alan@...rguk.ukuu.org.uk,
	Miao Xie <miaox@...fujitsu.com>,
	David Rientjes <rientjes@...gle.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Christoph Lameter <cl@...ux.com>
Subject: Re: [ 39/40] cpuset: mm: reduce large amounts of memory barrier
 related damage v3

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.krzesinski@...onical.com>
> > Signed-off-by: Mel Gorman <mgorman@...e.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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