[PATCH v2] mm/khugepaged: alloc_charge_hpage() take care of mem charge errors

[Peter Xu <peterx@redhat.com>]

If memory charge failed, instead of returning the hpage but with an error,
allow the function to cleanup the folio properly, which is normally what a
function should do in this case - either return successfully, or return
with no side effect of partial runs with an indicated error.

This will also avoid the caller calling mem_cgroup_uncharge() unnecessarily
with either anon or shmem path (even if it's safe to do so).

Cc: Yang Shi <shy828301@gmail.com>
Reviewed-by: David Stevens <stevensd@chromium.org>
Acked-by: Johannes Weiner <hannes@cmpxchg.org>
Signed-off-by: Peter Xu <peterx@redhat.com>
---
v1->v2:
- Enhance commit message, drop "Fixes:" and "Cc: stable" tag, add R-bs.
---
 mm/khugepaged.c | 9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

diff --git a/mm/khugepaged.c b/mm/khugepaged.c
index 8dbc39896811..941d1c7ea910 100644
--- a/mm/khugepaged.c
+++ b/mm/khugepaged.c
@@ -1063,12 +1063,19 @@ static int alloc_charge_hpage(struct page **hpage, struct mm_struct *mm,
 	gfp_t gfp = (cc->is_khugepaged ? alloc_hugepage_khugepaged_gfpmask() :
 		     GFP_TRANSHUGE);
 	int node = hpage_collapse_find_target_node(cc);
+	struct folio *folio;
 
 	if (!hpage_collapse_alloc_page(hpage, gfp, node, &cc->alloc_nmask))
 		return SCAN_ALLOC_HUGE_PAGE_FAIL;
-	if (unlikely(mem_cgroup_charge(page_folio(*hpage), mm, gfp)))
+
+	folio = page_folio(*hpage);
+	if (unlikely(mem_cgroup_charge(folio, mm, gfp))) {
+		folio_put(folio);
+		*hpage = NULL;
 		return SCAN_CGROUP_CHARGE_FAIL;
+	}
 	count_memcg_page_event(*hpage, THP_COLLAPSE_ALLOC);
+
 	return SCAN_SUCCEED;
 }
 
-- 
2.39.1