[PATCH v11 07/11] mm/hugetlb: Flush work when dissolving a HugeTLB page

[Muchun Song]

We should flush work when dissolving a HugeTLB page to make sure that
the HugeTLB page is freed to the buddy allocator. Because the caller
of dissolve_free_huge_pages() relies on this guarantee.

Signed-off-by: Muchun Song <songmuc...@bytedance.com>
Reviewed-by: Oscar Salvador <osalva...@suse.de>
---
 mm/hugetlb.c | 18 +++++++++++++++++-
 1 file changed, 17 insertions(+), 1 deletion(-)

diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index dbf4e8eeeff1..3e6aa6cc1f3e 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -1329,6 +1329,12 @@ static void update_hpage_vmemmap_workfn(struct 
work_struct *work)
 }
 static DECLARE_WORK(hpage_update_work, update_hpage_vmemmap_workfn);
 
+static inline void flush_hpage_update_work(struct hstate *h)
+{
+       if (free_vmemmap_pages_per_hpage(h))
+               flush_work(&hpage_update_work);
+}
+
 static inline void __update_and_free_page(struct hstate *h, struct page *page)
 {
        /* No need to allocate vmemmap pages */
@@ -1864,6 +1870,7 @@ static int free_pool_huge_page(struct hstate *h, 
nodemask_t *nodes_allowed,
 int dissolve_free_huge_page(struct page *page)
 {
        int rc = -EBUSY;
+       struct hstate *h = NULL;
 
        /* Not to disrupt normal path by vainly holding hugetlb_lock */
        if (!PageHuge(page))
@@ -1877,8 +1884,9 @@ int dissolve_free_huge_page(struct page *page)
 
        if (!page_count(page)) {
                struct page *head = compound_head(page);
-               struct hstate *h = page_hstate(head);
                int nid = page_to_nid(head);
+
+               h = page_hstate(head);
                if (h->free_huge_pages - h->resv_huge_pages == 0)
                        goto out;
 
@@ -1892,6 +1900,14 @@ int dissolve_free_huge_page(struct page *page)
        }
 out:
        spin_unlock(&hugetlb_lock);
+
+       /*
+        * We should flush work before return to make sure that
+        * the HugeTLB page is freed to the buddy.
+        */
+       if (!rc && h)
+               flush_hpage_update_work(h);
+
        return rc;
 }
 
-- 
2.11.0