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.
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?
Thanks,
Nish
--
Nishanth Aravamudan <[EMAIL PROTECTED]>
IBM Linux Technology Center
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