mm: hugetlb: avoid fallback for specific node allocation of 1G pages

commit 6d7bc93
Author: Luiz Capitulino <luizcap@redhat.com>
Date:   Mon Feb 10 22:48:56 2025 -0500

    mm: hugetlb: avoid fallback for specific node allocation of 1G pages

    When using the HugeTLB kernel command-line to allocate 1G pages from a
    specific node, such as:

       default_hugepagesz=1G hugepages=1:1

    If node 1 happens to not have enough memory for the requested number of 1G
    pages, the allocation falls back to other nodes.  A quick way to reproduce
    this is by creating a KVM guest with a memory-less node and trying to
    allocate 1 1G page from it.  Instead of failing, the allocation will
    fallback to other nodes.

    This defeats the purpose of node specific allocation.  Also, specific node
    allocation for 2M pages don't have this behavior: the allocation will just
    fail for the pages it can't satisfy.

    This issue happens because HugeTLB calls memblock_alloc_try_nid_raw() for
    1G boot-time allocation as this function falls back to other nodes if the
    allocation can't be satisfied.  Use memblock_alloc_exact_nid_raw()
    instead, which ensures that the allocation will only be satisfied from the
    specified node.

    Link: https://lkml.kernel.org/r/20250211034856.629371-1-luizcap@redhat.com
    Fixes: b538908 ("hugetlbfs: extend the definition of hugepages parameter to support node allocation")
    Signed-off-by: Luiz Capitulino <luizcap@redhat.com>
    Acked-by: Oscar Salvador <osalvador@suse.de>
    Acked-by: David Hildenbrand <david@redhat.com>
    Cc: "Mike Rapoport (IBM)" <rppt@kernel.org>
    Cc: Muchun Song <muchun.song@linux.dev>
    Cc: Zhenguo Yao <yaozhenguo1@gmail.com>
    Cc: Frank van der Linden <fvdl@google.com>
    Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

JIRA: https://issues.redhat.com/browse/RHEL-77742
Signed-off-by: Nico Pache <npache@redhat.com>

Author: PacheNico

mm/hugetlb.c

@@ -3139,7 +3139,7 @@ int __alloc_bootmem_huge_page(struct hstate *h, int nid)
 
 	/* do node specific alloc */
 	if (nid != NUMA_NO_NODE) {
-		m = memblock_alloc_try_nid_raw(huge_page_size(h), huge_page_size(h),
+		m = memblock_alloc_exact_nid_raw(huge_page_size(h), huge_page_size(h),
 				0, MEMBLOCK_ALLOC_ACCESSIBLE, nid);
 		if (!m)
 			return 0;