Messages in this thread | | | Subject | Re: [PATCH v3] mm: make expand_downwards symmetrical to expand_upwards | From | James Bottomley <> | Date | Tue, 19 Apr 2011 13:20:17 -0500 |
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On Tue, 2011-04-19 at 13:10 -0500, Christoph Lameter wrote: > On Tue, 19 Apr 2011, James Bottomley wrote: > > > > Right !NUMA systems only have node 0. > > > > That's rubbish. Discontigmem uses the nodes field to identify the > > discontiguous region. page_to_nid() returns this value. Your code > > wrongly assumes this is zero for non NUMA. > > Sorry the kernel has no node awareness if you do not set CONFIG_NUMA > > F.e. zone node lookups work the following way > > static inline int > zone_to_nid(struct zone *zone) > { > #ifdef CONFIG_NUMA > return zone->node; > #else > return 0; > #endif > } > > How in the world did you get a zone setup in node 1 with a !NUMA config?
I told you ... I forced an allocation into the first discontiguous region. That will return 1 for page_to_nid().
> The problem seems to be that the kernel seems to allow a > definition of a page_to_nid() function that returns non zero in the !NUMA > case.
This is called reality, yes.
> And slub relies on page_to_nid returning zero in the !NUMA case. > Because NODES_WIDTH should be 0 in the !NUMA case and therefore > page_to_nid must return 0.
right, that's what I told you: slub is broken because it's making a wrong assumption. Look in asm-generic/memory_model.h it shows how the page_to_nid() is used in finding the pfn array. DISCONTIGMEM uses some of the numa properties (including assigning zones to the discontiguous regions).
> > I can fix the panic by hard coding get_nodes() to return the zero node > > for the non-numa case ... however, presumably it's more than just this > > that's broken in slub? > > If you think that is broken then we have brokenness all over the kernel > whenever we determine the node from a page and use that to do a lookup.
Not really. The rest of the kernel uses the proper macros. in DISCONTIGMEM but !NUMA configs, the numa macros expand correctly. You've cut across that with all the CONFIG_NUMA checks in slub.
James
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