[PATCH 4/6] mm: hugetlb: add return -EAGAIN for dissolve_free_huge_page

Muchun Song
2021-01-04T07:03:53Z

When dissolve_free_huge_page() races with __free_huge_page(), we can
do a retry. Because the race window is small.

Signed-off-by: Muchun Song <songmuchun@bytedance.com>
---
mm/hugetlb.c | 16 +++++++++++-----
1 file changed, 11 insertions(+), 5 deletions(-)

diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index 72608008f8b4..db00ae375d2a 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -1763,10 +1763,11 @@ static int free_pool_huge_page(struct hstate *h, nodemask_t *nodes_allowed,
* nothing for in-use hugepages and non-hugepages.
* This function returns values like below:
*
- * -EBUSY: failed to dissolved free hugepages or the hugepage is in-use
- * (allocated or reserved.)
- * 0: successfully dissolved free hugepages or the page is not a
- * hugepage (considered as already dissolved)
+ * -EAGAIN: race with __free_huge_page() and can do a retry
+ * -EBUSY: failed to dissolved free hugepages or the hugepage is in-use
+ * (allocated or reserved.)
+ * 0: successfully dissolved free hugepages or the page is not a
+ * hugepage (considered as already dissolved)
*/
int dissolve_free_huge_page(struct page *page)
{
@@ -1815,8 +1816,10 @@ int dissolve_free_huge_page(struct page *page)
* We should make sure that the page is already on the free list
* when it is dissolved.
*/
- if (unlikely(!PageHugeFreed(head)))
+ if (unlikely(!PageHugeFreed(head))) {
+ rc = -EAGAIN;
goto out;
+ }

/*
* Move PageHWPoison flag from head page to the raw error page,
@@ -1857,7 +1860,10 @@ int dissolve_free_huge_pages(unsigned long start_pfn, unsigned long end_pfn)

for (pfn = start_pfn; pfn < end_pfn; pfn += 1 << minimum_order) {
page = pfn_to_page(pfn);
+retry:
rc = dissolve_free_huge_page(page);
+ if (rc == -EAGAIN)
+ goto retry;
if (rc)
break;
}
--
2.11.0