Re: [PATCH v5 02/11] mm/mempolicy: introduce MPOL_WEIGHTED_INTERLEAVE for weighted interleaving

Gregory Price [off-list ref] writes:

On Fri, Jan 05, 2024 at 02:51:40PM +0800, Huang, Ying wrote:

quoted

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So we're talking ~1MB for 1024 threads with mempolicies to avoid error
conditions mid-page-allocation and to reduce the cost associated with
applying weighted interleave.

Think about this again.  Why do we need weights array on stack?  I think
this is used to keep weights consistent.  If so, we don't need weights
array on stack.  Just use RCU to access global weights array.

From the bulk allocation code:

__alloc_pages_bulk(gfp, node, NULL, node_pages, NULL, page_array);

This function can block. You cannot block during an RCU read context.

Yes.  You are right.  For __alloc_pages_bulk(), it should be OK to
allocate the weights array.  For weighted_interleave_nid(), we can use
RCU to avoid memory allocation in relative fast code path.

BTW, we can use nr_node_ids instead of MAX_NUMNODES if applicable.

--
Best Regards,
Huang, Ying