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

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Date:   Wed, 22 Feb 2023 14:52:47 -0500
From:   Peter Xu <peterx@...hat.com>
To:     linux-kernel@...r.kernel.org, linux-mm@...ck.org
Cc:     peterx@...hat.com, Andrew Morton <akpm@...ux-foundation.org>,
        Yang Shi <shy828301@...il.com>,
        David Stevens <stevensd@...omium.org>,
        Johannes Weiner <hannes@...xchg.org>
Subject: [PATCH v2] mm/khugepaged: alloc_charge_hpage() take care of mem charge errors

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@...il.com>
Reviewed-by: David Stevens <stevensd@...omium.org>
Acked-by: Johannes Weiner <hannes@...xchg.org>
Signed-off-by: Peter Xu <peterx@...hat.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