MPI 4.0: Allow MPI_WIN_SHARED_QUERY on regular windows

[devreal]

MPI 4.0 allows MPI_WIN_SHARED_QUERY to be called on any allocated and created windows. It may return the pointer, size, and displacement unit if the peer is located on the same node and the memory is shared.

This PR adds this functionality for osc/sm and osc/rdma. There is an attempt to implement it in osc/ucx but it's incomplete. We need to exchange and store the base pointer for the peer processes on the same node so we can pass them to ucp_rkey_ptr(). I'm not sure how to easily determine whether a process is on the same node. Some help would be appreciated.

[devreal]

I think I got this working now with osc/sm, osc/rdma, and osc/ucx. osc/portals does not provide a shared_query callback, which we handle gracefully. That should cover all osc.

I have a test case for it but I'm not sure where to put it. It's hard to make this a hard test because whether or not the underlying implementation (like UCX) provide shared memory support. It can be used to check that we don't have a hard fail anywhere.

[Copilot]

Pull Request Overview

This PR implements MPI 4.0 functionality that allows MPI_WIN_SHARED_QUERY to be called on any allocated and created windows, not just shared memory windows. The function may return the pointer, size, and displacement unit if the peer is located on the same node and the memory is shared.

• Adds support for MPI_WIN_SHARED_QUERY on regular windows in OSC/SM and OSC/RDMA modules
• Modifies the core win_shared_query function to gracefully handle unsupported cases
• Includes partial implementation for OSC/UCX (incomplete according to PR description)

Reviewed Changes

Copilot reviewed 7 out of 7 changed files in this pull request and generated 4 comments.

Show a summary per file

File	Description
ompi/mpi/c/win_shared_query.c.in	Updates core function to handle unsupported cases gracefully instead of raising errors
ompi/mca/osc/ucx/osc_ucx_component.c	Adds shared query support for UCX with optimization for size/displacement unit handling
ompi/mca/osc/ucx/osc_ucx.h	Adds helper functions and structure fields for size and displacement unit management
ompi/mca/osc/sm/osc_sm_component.c	Removes flavor restriction for shared memory module and fixes alignment calculations
ompi/mca/osc/rdma/osc_rdma_peer.h	Adds CPU atomics flag and helper function for peer capabilities
ompi/mca/osc/rdma/osc_rdma_component.c	Implements shared query for RDMA module and updates peer flag handling
ompi/mca/osc/rdma/osc_rdma_accumulate.c	Updates atomic operations to use new CPU atomics check instead of local base check

Comments suppressed due to low confidence (2)

ompi/mca/osc/sm/osc_sm_component.c:286

• This line was removed but the assignment to total is still needed for the non-contiguous case. The variable total should be assigned the page-aligned size when module->noncontig is true.

        } else {

ompi/mca/osc/sm/osc_sm_component.c:288

• This line was removed but the assignment to total is still needed for the contiguous case. The variable total should be assigned the actual size when module->noncontig is false.

                                "allocating window using contiguous strategy");

[devreal]

I squashed everything down to one commit. This should be ready for review.