From: Barry Song song.bao.hua@hisilicon.com Subject: mm/cma.c: use exact_nid true to fix possible per-numa cma leak

Calling cma_declare_contiguous_nid() with false exact_nid for per-numa reservation can easily cause cma leak and various confusion. For example, mm/hugetlb.c is trying to reserve per-numa cma for gigantic pages. But it can easily leak cma and make users confused when system has memoryless nodes.

In case the system has 4 numa nodes, and only numa node0 has memory. if we set hugetlb_cma=4G in bootargs, mm/hugetlb.c will get 4 cma areas for 4 different numa nodes. since exact_nid=false in current code, all 4 numa nodes will get cma successfully from node0, but hugetlb_cma[1 to 3] will never be available to hugepage will only allocate memory from hugetlb_cma[0].

In case the system has 4 numa nodes, both numa node0&2 has memory, other nodes have no memory. if we set hugetlb_cma=4G in bootargs, mm/hugetlb.c will get 4 cma areas for 4 different numa nodes. since exact_nid=false in current code, all 4 numa nodes will get cma successfully from node0 or 2, but hugetlb_cma[1] and [3] will never be available to hugepage as mm/hugetlb.c will only allocate memory from hugetlb_cma[0] and hugetlb_cma[2]. This causes permanent leak of the cma areas which are supposed to be used by memoryless node.

Of cource we can workaround the issue by letting mm/hugetlb.c scan all cma areas in alloc_gigantic_page() even node_mask includes node0 only. that means when node_mask includes node0 only, we can get page from hugetlb_cma[1] to hugetlb_cma[3]. But this will cause kernel crash in free_gigantic_page() while it wants to free page by: cma_release(hugetlb_cma[page_to_nid(page)], page, 1 << order)

On the other hand, exact_nid=false won't consider numa distance, it might be not that useful to leverage cma areas on remote nodes. I feel it is much simpler to make exact_nid true to make everything clear. After that, memoryless nodes won't be able to reserve per-numa CMA from other nodes which have memory.

Link: http://lkml.kernel.org/r/20200628074345.27228-1-song.bao.hua@hisilicon.com Fixes: cf11e85fc08c ("mm: hugetlb: optionally allocate gigantic hugepages using cma") Signed-off-by: Barry Song song.bao.hua@hisilicon.com Acked-by: Roman Gushchin guro@fb.com Cc: Jonathan Cameron Jonathan.Cameron@huawei.com Cc: Aslan Bakirov aslan@fb.com Cc: Michal Hocko mhocko@kernel.org Cc: Andreas Schaufler andreas.schaufler@gmx.de Cc: Mike Kravetz mike.kravetz@oracle.com Cc: Rik van Riel riel@surriel.com Cc: Joonsoo Kim js1304@gmail.com Cc: Robin Murphy robin.murphy@arm.com Cc: stable@vger.kernel.org Signed-off-by: Andrew Morton akpm@linux-foundation.org ---

mm/cma.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-)

--- a/mm/cma.c~mm-cmac-use-exact_nid-true-to-fix-possible-per-numa-cma-leak +++ a/mm/cma.c @@ -339,13 +339,13 @@ int __init cma_declare_contiguous_nid(ph */ if (base < highmem_start && limit > highmem_start) { addr = memblock_alloc_range_nid(size, alignment, - highmem_start, limit, nid, false); + highmem_start, limit, nid, true); limit = highmem_start; }

if (!addr) { addr = memblock_alloc_range_nid(size, alignment, base, - limit, nid, false); + limit, nid, true); if (!addr) { ret = -ENOMEM; goto err; _