Subject: Re: [PATCH] slub: Don't throw away partial remote slabs if there is no local memory

From: Joonsoo Kim <[email-masked]>
Date: Tue, 7 Jan 2014 18:10:16 +0900

On Tue, Jan 07, 2014 at 04:48:40PM +0800, Wanpeng Li wrote:
> Hi Joonsoo,
> On Tue, Jan 07, 2014 at 04:41:36PM +0900, Joonsoo Kim wrote:
> >On Tue, Jan 07, 2014 at 01:21:00PM +1100, Anton Blanchard wrote:
> >> 
> [...]
> >Hello,
> >
> >I think that we need more efforts to solve unbalanced node problem.
> >
> >With this patch, even if node of current cpu slab is not favorable to
> >unbalanced node, allocation would proceed and we would get the unintended memory.
> >
> 
> We have a machine:
> 
> [    0.000000] Node 0 Memory:
> [    0.000000] Node 4 Memory: 0x0-0x10000000 0x20000000-0x60000000 0x80000000-0xc0000000
> [    0.000000] Node 6 Memory: 0x10000000-0x20000000 0x60000000-0x80000000
> [    0.000000] Node 10 Memory: 0xc0000000-0x180000000
> 
> [    0.041486] Node 0 CPUs: 0-19
> [    0.041490] Node 4 CPUs:
> [    0.041492] Node 6 CPUs:
> [    0.041495] Node 10 CPUs:
> 
> The pages of current cpu slab should be allocated from fallback zones/nodes 
> of the memoryless node in buddy system, how can not favorable happen? 

Hi, Wanpeng.

IIRC, if we call kmem_cache_alloc_node() with certain node #, we try to
allocate the page in fallback zones/node of that node #. So fallback list isn't
related to fallback one of memoryless node #. Am I wrong?

Thanks.

> 
> >And there is one more problem. Even if we have some partial slabs on
> >compatible node, we would allocate new slab, because get_partial() cannot handle
> >this unbalance node case.
> >
> >To fix this correctly, how about following patch?
> >
> 
> So I think we should fold both of your two patches to one.
> 
> Regards,
> Wanpeng Li 
> 
> >Thanks.
> >
> >------------->8--------------------
> >diff --git a/mm/slub.c b/mm/slub.c
> >index c3eb3d3..a1f6dfa 100644
> >--- a/mm/slub.c
> >+++ b/mm/slub.c
> >@@ -1672,7 +1672,19 @@ static void *get_partial(struct kmem_cache *s, gfp_t flags, int node,
> > {
> >        void *object;
> >        int searchnode = (node == NUMA_NO_NODE) ? numa_node_id() : node;
> >+       struct zonelist *zonelist;
> >+       struct zoneref *z;
> >+       struct zone *zone;
> >+       enum zone_type high_zoneidx = gfp_zone(flags);
> >
> >+       if (!node_present_pages(searchnode)) {
> >+               zonelist = node_zonelist(searchnode, flags);
> >+               for_each_zone_zonelist(zone, z, zonelist, high_zoneidx) {
> >+                       searchnode = zone_to_nid(zone);
> >+                       if (node_present_pages(searchnode))
> >+                               break;
> >+               }
> >+       }
> >        object = get_partial_node(s, get_node(s, searchnode), c, flags);
> >        if (object || node != NUMA_NO_NODE)
> >                return object;
> >
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