Messages in this thread | | | Subject | Re: [PATCH 6/6] Use one zonelist that is filtered by nodemask | From | Lee Schermerhorn <> | Date | Fri, 09 Nov 2007 12:18:52 -0500 |
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On Fri, 2007-11-09 at 08:45 -0800, Nishanth Aravamudan wrote: > On 09.11.2007 [16:14:55 +0000], Mel Gorman wrote: > > On (09/11/07 07:45), Christoph Lameter didst pronounce: > > > On Fri, 9 Nov 2007, Mel Gorman wrote: > > > > > > > struct page * fastcall > > > > __alloc_pages(gfp_t gfp_mask, unsigned int order, > > > > struct zonelist *zonelist) > > > > { > > > > + /* > > > > + * Use a temporary nodemask for __GFP_THISNODE allocations. If the > > > > + * cost of allocating on the stack or the stack usage becomes > > > > + * noticable, allocate the nodemasks per node at boot or compile time > > > > + */ > > > > + if (unlikely(gfp_mask & __GFP_THISNODE)) { > > > > + nodemask_t nodemask; > > > > > > Hmmm.. This places a potentially big structure on the stack. nodemask can > > > contain up to 1024 bits which means 128 bytes. Maybe keep an array of > > > gfp_thisnode nodemasks (node_nodemask?) and use node_nodemask[nid]? > > > > > > > That is what I was hinting at in the comment as a possible solution. > > > > > > + > > > > + return __alloc_pages_internal(gfp_mask, order, > > > > + zonelist, nodemask_thisnode(numa_node_id(), &nodemask)); > > > > > > Argh.... GFP_THISNODE must use the nid passed to alloc_pages_node > > > and *not* the local numa node id. Only if the node specified to > > > alloc_pages nodes is -1 will this work. > > > > > > > alloc_pages_node() calls __alloc_pages_nodemask() though where in this > > function if I'm reading it right is called without a node id. Given no > > other details on the nid, the current one seemed a logical choice. > > Yeah, I guess the context here matters (and is a little hard to follow > because thare are a few places that change in different ways here): > > For allocating pages from a particular node (GFP_THISNODE with nid), > the nid clearly must be specified. This only happens with > alloc_pages_node(), AFAICT. So, in that interface, the right thing is > done and the appropriate nodemask will be built.
I agree. In an earlier patch, Mel was ignoring nid and using numa_node_id() here. This was causing your [Nish's] hugetlb pool allocation patches to fail. Mel fixed that ~9oct07.
> > On the other hand, if we call alloc_pages() with GFP_THISNODE set, there > is no nid to base the allocation on, so we "fallback" to numa_node_id() > [ almost like the nid had been specified as -1 ]. > > So I guess this is logical -- but I wonder, do we have any callers of > alloc_pages(GFP_THISNODE) ? It seems like an odd thing to do, when > alloc_pages_node() exists?
I don't know if we have any current callers that do this, but absent any documentation specifying otherwise, Mel's implementation matches what I'd expect the behavior to be if I DID call alloc_pages with 'THISNODE. However, we could specify that THISNODE is ignored in __alloc_pages() and recommend the use of alloc_pages_node() passing numa_node_id() as the nid parameter to achieve the behavior. This would eliminate the check for 'THISNODE in __alloc_pages(). Just mask it off before calling down to __alloc_pages_internal().
Does this make sense?
Lee
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