When trying to allocate a hugepage with none reserved ones free, it may be allowed in case a number of overcommit hugepages was configured (using /proc/sys/vm/nr_overcommit_hugepages) and that number wasn't reached. This allows for a behavior of having extra hugepages allocated dynamically, if there're resources for it. Some sysadmins even prefer not reserving any hugepages and setting a big number of overcommit hugepages.

But while attempting to allocate overcommit hugepages in a multi node system (either NUMA or mempolicy/cpuset) said allocations might randomly fail even when there're resources available for the allocation.

This happens due allowed_mems_nr() only accounting for the number of free hugepages in the nodes the current process belongs to and the surplus hugepage allocation is done so it can be allocated in any node. In case one or more of the requested surplus hugepages are allocated in a different node, the whole allocation will fail due allowed_mems_nr() returning a lower value.

So allocate surplus hugepages in one of the nodes the current process belongs to.

Easy way to reproduce this issue is to use a 2+ NUMA nodes system:

# echo 0 >/proc/sys/vm/nr_hugepages # echo 1 >/proc/sys/vm/nr_overcommit_hugepages # numactl -m0 ./tools/testing/selftests/mm/map_hugetlb 2

Repeating the execution of map_hugetlb test application will eventually fail when the hugepage ends up allocated in a different node.

v2: - attempt to make the description more clear - prevent unitialized usage of folio in case current process isn't part of any nodes with memory

Cc: Vishal Moola vishal.moola@gmail.com Cc: David Hildenbrand david@redhat.com Cc: Aristeu Rozanski aris@redhat.com Cc: Muchun Song muchun.song@linux.dev Cc: Andrew Morton akpm@linux-foundation.org Cc: stable@vger.kernel.org Signed-off-by: Aristeu Rozanski aris@ruivo.org

--- mm/hugetlb.c | 47 ++++++++++++++++++++++++++++------------------- 1 file changed, 28 insertions(+), 19 deletions(-)

--- upstream.orig/mm/hugetlb.c 2024-06-20 13:42:25.699568114 -0400 +++ upstream/mm/hugetlb.c 2024-07-01 16:48:53.693298053 -0400 @@ -2618,6 +2618,23 @@ struct folio *alloc_hugetlb_folio_nodema return alloc_migrate_hugetlb_folio(h, gfp_mask, preferred_nid, nmask); }

+static nodemask_t *policy_mbind_nodemask(gfp_t gfp) +{ +#ifdef CONFIG_NUMA + struct mempolicy *mpol = get_task_policy(current); + + /* + * Only enforce MPOL_BIND policy which overlaps with cpuset policy + * (from policy_nodemask) specifically for hugetlb case + */ + if (mpol->mode == MPOL_BIND && + (apply_policy_zone(mpol, gfp_zone(gfp)) && + cpuset_nodemask_valid_mems_allowed(&mpol->nodes))) + return &mpol->nodes; +#endif + return NULL; +} + /* * Increase the hugetlb pool such that it can accommodate a reservation * of size 'delta'. @@ -2631,6 +2648,8 @@ static int gather_surplus_pages(struct h long i; long needed, allocated; bool alloc_ok = true; + int node; + nodemask_t *mbind_nodemask = policy_mbind_nodemask(htlb_alloc_mask(h));

lockdep_assert_held(&hugetlb_lock); needed = (h->resv_huge_pages + delta) - h->free_huge_pages; @@ -2645,8 +2664,15 @@ allocated = 0; retry: spin_unlock_irq(&hugetlb_lock); for (i = 0; i < needed; i++) { - folio = alloc_surplus_hugetlb_folio(h, htlb_alloc_mask(h), - NUMA_NO_NODE, NULL); + folio = NULL; + for_each_node_mask(node, cpuset_current_mems_allowed) { + if (!mbind_nodemask || node_isset(node, *mbind_nodemask)) { + folio = alloc_surplus_hugetlb_folio(h, htlb_alloc_mask(h), + node, NULL); + if (folio) + break; + } + } if (!folio) { alloc_ok = false; break; @@ -4876,23 +4902,6 @@ default_hstate_max_huge_pages = 0; } __setup("default_hugepagesz=", default_hugepagesz_setup);

-static nodemask_t *policy_mbind_nodemask(gfp_t gfp) -{ -#ifdef CONFIG_NUMA - struct mempolicy *mpol = get_task_policy(current); - - /* - * Only enforce MPOL_BIND policy which overlaps with cpuset policy - * (from policy_nodemask) specifically for hugetlb case - */ - if (mpol->mode == MPOL_BIND && - (apply_policy_zone(mpol, gfp_zone(gfp)) && - cpuset_nodemask_valid_mems_allowed(&mpol->nodes))) - return &mpol->nodes; -#endif - return NULL; -} - static unsigned int allowed_mems_nr(struct hstate *h) { int node;