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>
---
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 | 19 ++++++++++++++++---
1 file changed, 16 insertions(+), 3 deletions(-)
diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index 2a554f006255..bdc4499f324b 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;
/*
@@ -3315,7 +3314,8 @@ static int set_max_huge_pages(struct hstate *h, unsigned long count, int nid,
* the user tries to allocate gigantic pages but let the user free the
* boottime allocated gigantic pages.
*/
- if (hstate_is_gigantic(h) && !IS_ENABLED(CONFIG_CONTIG_ALLOC)) {
+ if (hstate_is_gigantic(h) && (!IS_ENABLED(CONFIG_CONTIG_ALLOC) ||
+ !gigantic_page_runtime_supported())) {
if (count > persistent_huge_pages(h)) {
spin_unlock_irq(&hugetlb_lock);
mutex_unlock(&h->resize_lock);
@@ -3363,6 +3363,19 @@ static int set_max_huge_pages(struct hstate *h, unsigned long count, int nid,
goto out;
}
+ /*
+ * We can not decrease gigantic pool size if runtime modification
+ * is not supported.
+ */
+ if (hstate_is_gigantic(h) && !gigantic_page_runtime_supported()) {
+ if (count < persistent_huge_pages(h)) {
+ spin_unlock_irq(&hugetlb_lock);
+ mutex_unlock(&h->resize_lock);
+ NODEMASK_FREE(node_alloc_noretry);
+ return -EINVAL;
+ }
+ }
+
/*
* Decrease the pool size
* First return free pages to the buddy allocator (being careful
--
2.25.1
