On Fri, 2007-11-09 at 08:45 -0800, Nishanth Aravamudan wrote:

On 09.11.2007 [16:14:55 +0000], Mel Gorman wrote:

quoted

On (09/11/07 07:45), Christoph Lameter didst pronounce:

quoted

On Fri, 9 Nov 2007, Mel Gorman wrote:

quoted

 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.

quoted

quoted

+
+		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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