From c0531714d6e3fd720b7dacc2de2d0503a995bcdc Mon Sep 17 00:00:00 2001 From: Naoya Horiguchi Date: Thu, 14 Jul 2022 13:24:13 +0900 Subject: [PATCH] mm/hugetlb: check gigantic_page_runtime_supported() in return_unused_surplus_pages() Patch series "mm, hwpoison: enable 1GB hugepage support", v7. This patch (of 8): I found a weird state of 1GB hugepage pool, caused by the following procedure: - run a process reserving all free 1GB hugepages, - shrink free 1GB hugepage pool to zero (i.e. writing 0 to /sys/kernel/mm/hugepages/hugepages-1048576kB/nr_hugepages), then - kill the reserving process. , then all the hugepages are free *and* surplus at the same time. $ cat /sys/kernel/mm/hugepages/hugepages-1048576kB/nr_hugepages 3 $ cat /sys/kernel/mm/hugepages/hugepages-1048576kB/free_hugepages 3 $ cat /sys/kernel/mm/hugepages/hugepages-1048576kB/resv_hugepages 0 $ cat /sys/kernel/mm/hugepages/hugepages-1048576kB/surplus_hugepages 3 This state is resolved by reserving and allocating the pages then freeing them again, so this seems not to result in serious problem. But it's a little surprising (shrinking pool suddenly fails). This behavior is caused by hstate_is_gigantic() check in return_unused_surplus_pages(). This was introduced so long ago in 2008 by commit aa888a74977a ("hugetlb: support larger than MAX_ORDER"), and at that time the gigantic pages were not supposed to be allocated/freed at run-time. Now kernel can support runtime allocation/free, so let's check gigantic_page_runtime_supported() together. Link: https://lkml.kernel.org/r/20220714042420.1847125-1-naoya.horiguchi@linux.dev Link: https://lkml.kernel.org/r/20220714042420.1847125-2-naoya.horiguchi@linux.dev Signed-off-by: Naoya Horiguchi Reviewed-by: Miaohe Lin Cc: David Hildenbrand Cc: Mike Kravetz Cc: Liu Shixin Cc: Yang Shi Cc: Oscar Salvador Cc: Muchun Song Cc: kernel test robot Signed-off-by: Andrew Morton --- mm/hugetlb.c | 3 +-- 1 file changed, 1 insertion(+), 2 deletions(-) diff --git a/mm/hugetlb.c b/mm/hugetlb.c index 598c372..ee6655e 100644 --- a/mm/hugetlb.c +++ b/mm/hugetlb.c @@ -2432,8 +2432,7 @@ static void return_unused_surplus_pages(struct hstate *h, /* Uncommit the reservation */ h->resv_huge_pages -= unused_resv_pages; - /* Cannot return gigantic pages currently */ - if (hstate_is_gigantic(h)) + if (hstate_is_gigantic(h) && !gigantic_page_runtime_supported()) goto out; /* -- 2.7.4