Messages in this thread Patch in this message | | | From | Naoya Horiguchi <> | Subject | [mm-unstable PATCH v5 1/8] mm/hugetlb: check gigantic_page_runtime_supported() in return_unused_surplus_pages() | Date | Fri, 8 Jul 2022 14:36:46 +0900 |
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From: Naoya Horiguchi <naoya.horiguchi@nec.com>
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.
Signed-off-by: Naoya Horiguchi <naoya.horiguchi@nec.com> --- v4 -> v5: - drop additional gigantic_page_runtime_supported() checks.
v2 -> v3: - Fixed typo in patch description, - add !gigantic_page_runtime_supported() check instead of removing hstate_is_gigantic() check (suggested by Miaohe and Muchun) - add a few more !gigantic_page_runtime_supported() check in set_max_huge_pages() (by Mike). --- mm/hugetlb.c | 3 +-- 1 file changed, 1 insertion(+), 2 deletions(-)
diff --git a/mm/hugetlb.c b/mm/hugetlb.c index a4506ed1f1db..cf8ccee7654c 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; /* -- 2.25.1
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