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: b5389086ad7b ("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>

diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index 65068671e460ac1252e6ef5934de3c855f7acb5d..163190e89ea16450026496c020b544877db147d1 100644 (file)
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -3145,7 +3145,7 @@ 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;