On Mon, 11 Aug 2014, Vladimir Davydov wrote:
> > diff --git a/mm/slab.c b/mm/slab.c
> > --- a/mm/slab.c
> > +++ b/mm/slab.c
> > @@ -3047,16 +3047,19 @@ retry:
> > * from existing per node queues.
> > */
> > for_each_zone_zonelist(zone, z, zonelist, high_zoneidx) {
> > - nid = zone_to_nid(zone);
> > + struct kmem_cache_node *n;
> >
> > - if (cpuset_zone_allowed_hardwall(zone, flags) &&
> > - get_node(cache, nid) &&
> > - get_node(cache, nid)->free_objects) {
> > - obj = ____cache_alloc_node(cache,
> > - flags | GFP_THISNODE, nid);
> > - if (obj)
> > - break;
> > - }
> > + nid = zone_to_nid(zone);
> > + if (!cpuset_zone_allowed(zone, flags | __GFP_HARDWALL))
>
> We must use softwall check here, otherwise we will proceed to
> alloc_pages even if there are lots of free slabs on other nodes.
> alloc_pages, in turn, may allocate from other nodes in case
> cpuset.mem_hardwall=0, because it uses softwall check, so it may add yet
> another free slab to another node's list even if it isn't empty. As a
> result, we may get free list bloating on other nodes. I've seen a
> machine with one of its nodes almost completely filled with inactive
> slabs for buffer_heads (dozens of GBs) w/o any chance to drop them. So,
> this is a bug that must be fixed.
>
Right, I understand, and my patch makes no attempt to fix that issue, it's
simply collapsing the code down into a single cpuset_zone_allowed()
function and the context for the allocation is controlled by the gfp
flags (and hardwall is controlled by setting __GFP_HARDWALL) as it should
be. I understand the issue you face, but I can't combine a cleanup with a
fix and I would prefer to have your patch keep your commit description.
The diffstat for my proposal removes many more lines than it adds and I
think it will avoid this type of issue in the future for new callers.
Your patch could then be based on the single cpuset_zone_allowed()
function where you would simply have to remove the __GFP_HARDWALL above.
Or, your patch could be merged first and then my cleanup on top, but it
seems like your one-liner would be more clear if it is based on mine.
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