From: Naoya Horiguchi <naoya.horiguchi@xxxxxxx>
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@xxxxxxx>
---
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
