[LU-15189] GDS support improvements and fixes.

• Type: Bug
• Status: Resolved
• Priority: Critical
• Resolution: Fixed
• Fix Version/s: Lustre 2.16.0
• Labels: patch
• Severity: 3
• Assignee: Alexey Lyashkov
• Reporter: Alexey Lyashkov

Description

Whamcloud GDS code have several oddness.
1. Lack of autoconf support it caused a wrong structure / macros used for GDS<>Lustre interaction.
(changed in the last nvidia-fs code).

2. GDS have a bug in page state testing function. It caused a set force_rdma flag to the ptlrpc message buffer. It's because

bool nvfs_is_gpu_page(struct page *page)
{
        nvfs_mgroup_ptr_t nvfs_mgroup;

        nvfs_mgroup = __nvfs_mgroup_from_page(page, false);
        if (nvfs_mgroup == NULL) {
                return false;
        } else if (unlikely(IS_ERR(nvfs_mgroup))) {
                // This is a GPU page but we did not take reference as we are in shutdown path
                // But, we will return true to the caller so that caller doesn't think it is a
                // CPU page and fall back to CPU path 
                return true; <<< true if no magic.

It's very easy to detect - just push force_rdma flag into memory mapping function and check is force_rdma buffer can mapped with GDS code.
But instead of invest it, Whamcloud adds an odd workaround which tries to execute a both mapping functions who caused an lnet slowness.

Lets fix it.