Re: [PATCH] mv clear node_load[] to __build_all_zonelists()

[KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>]

On Mon, 17 Aug 2009 14:34:47 -0700
Andrew Morton <akpm@linux-foundation.org> wrote:

> On Thu, 6 Aug 2009 19:50:37 +0900
> KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com> wrote:
> 
> > On Thu, 6 Aug 2009 18:44:40 +0800
> > Bo Liu <bo-liu@hotmail.com> wrote:
> > 
> > > 
> > >  If node_load[] is cleared everytime build_zonelists() is called,node_load[]
> > >  will have no help to find the next node that should appear in the given node's
> > >  fallback list.
> > >  Signed-off-by: Bob Liu 
> > 
> > nice catch. (my old bug...sorry
> > 
> > Reviewed-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
> > 
> > BTW, do you have special reasons to hide your mail address in commit log ?
> > 
> > I added proper CC: list.
> > Hmm, I think it's necessary to do total review/rewrite this function again..
> > 
> > 
> > > ---
> > >  mm/page_alloc.c |    2 +-
> > >  1 files changed, 1 insertions(+), 1 deletions(-)
> > >  
> > > diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> > > index d052abb..72f7345 100644
> > > --- a/mm/page_alloc.c
> > > +++ b/mm/page_alloc.c
> > > @@ -2544,7 +2544,6 @@ static void build_zonelists(pg_data_t *pgdat)
> > >  	prev_node = local_node;
> > >  	nodes_clear(used_mask);
> > >  
> > > -	memset(node_load, 0, sizeof(node_load));
> > >  	memset(node_order, 0, sizeof(node_order));
> > >  	j = 0;
> > >  
> > > @@ -2653,6 +2652,7 @@ static int __build_all_zonelists(void *dummy)
> > >  {
> > >  	int nid;
> > >  
> > > +	memset(node_load, 0, sizeof(node_load));
> > >  	for_each_online_node(nid) {
> > >  		pg_data_t *pgdat = NODE_DATA(nid);
> 
> What are the consequences of this bug?
> 
> Is the fix needed in 2.6.31?  Earlier?
> 
I think this should be on fast-track as bugfix.

By this bug, zonelist's node_order is not calculated as expected.
This bug affects on big machine, which has asynmetric node distance.

[synmetric NUMA's node distance]
     0    1    2
0   10   12   12
1   12   10   12
2   12   12   10

[asynmetric NUMA's node distance]
     0    1    2
0   10   12   20
1   12   10   14
2   20   14   10


This (my bug) is very old..but no one have reported this for a long time.
Maybe because the number of asynmetric NUMA is very small and they use cpuset
for customizing node memory allocation fallback.

Thanks,
-Kame

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