Re: [PATCH] mm/hugetlb: account for allowed nodes when gathering surplus pages

[Muchun Song <muchun.song@linux.dev>]

> On Sep 9, 2026, at 15:46, Huaisheng Ye <yehuaisheng@open-hieco.net> wrote:
> 
> Hugetlb reservations are accounted globally, but hugetlb_acct_memory()
> also verifies that the current cpuset and MPOL_BIND policy contain enough
> free huge pages to add a new reservation.
> 
> gather_surplus_pages() calculates its allocation shortfall from the global
> free and reserved counters. If the global pool has enough free pages, but
> those pages reside outside the nodes allowed by the task, it allocates no
> surplus pages. The subsequent allowed_mems_nr() check then rejects the
> reservation and mmap() fails with ENOMEM, even when
> nr_overcommit_hugepages permits allocating surplus pages on the allowed
> nodes.
> 
> Calculate both the global shortfall and the shortfall within the allowed
> nodes, and allocate the larger of the two. Include surplus pages allocated
> outside hugetlb_lock in both calculations when rechecking after reacquiring
> the lock. These pages are constrained by alloc_nodemask, so they satisfy
> both shortages.
> 
> Easy way to reproduce this issue with 2+ NUMA nodes system:
> 
>  # echo 0 > /sys/kernel/mm/hugepages/hugepages-2048kB/nr_hugepage
>  # echo 3 > /sys/devices/system/node/node0/hugepages/hugepages-2048kB/nr_hugepages
>  # echo 1 > /sys/kernel/mm/hugepages/hugepages-2048kB/nr_overcommit_hugepages
>  # cd tools/testing/selftests/mm
>  # numactl --membind=1 ./hugetlb-mmap 2 21
>  TAP version 13
>  # [INFO] detected hugetlb page size: 2048 KiB
>  # [INFO] detected hugetlb page size: 1048576 KiB
>  # 2048 kB hugepages
>  1..2
>  # Mapping 2 Mbytes
>  Bail out! mmap: Cannot allocate memory (12)
>  # Planned tests != run tests (2 != 0)
>  # Totals: pass:0 fail:0 xfail:0 xpass:0 skip:0 error:0
> 
> This fixes hugetlb mappings when, for example, a task runs with
> MPOL_BIND on Node 1 while the existing free huge pages are on Node 0.
> 
> Similar issue also could be found in ltp if the free pages of global pool
> reside outside the nodes allowed by the application.
>  # cd ltp/testcases/kernel/mem/hugetlb/hugemmap/
>  # numactl --cpunodebind=0 --membind=1 ./hugemmap10
> 
> Signed-off-by: Huaisheng Ye <yehuaisheng@open-hieco.net>

Acked-by: Muchun Song <muchun.song@linux.dev>

Thanks.