From:   Peter Xu <peterx@redhat.com>
To:     linux-mm@kvack.org, linux-kernel@vger.kernel.org
Cc:     David Stevens <stevensd@chromium.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        Yang Shi <shy828301@gmail.com>, peterx@redhat.com,
        Johannes Weiner <hannes@cmpxchg.org>,
        Zach O'Keefe <zokeefe@google.com>
Subject: [PATCH] mm/khugepaged: Cleanup memcg uncharge for failure path
Date:   Fri,  3 Mar 2023 10:12:18 -0500
Message-Id: <20230303151218.311015-1-peterx@redhat.com>
MIME-Version: 1.0
Content-Transfer-Encoding: 8bit
Precedence: bulk

Explicit memcg uncharging is not needed when the memcg accounting has the
same lifespan of the page/folio.  That becomes the case for khugepaged
after Yang & Zach's recent rework so the hpage will be allocated for each
collapse rather than being cached.

Cleanup the explicit memcg uncharge in khugepaged failure path and leave
that for put_page().

Suggested-by: Zach O'Keefe <zokeefe@google.com>
Signed-off-by: Peter Xu <peterx@redhat.com>
---
 mm/khugepaged.c | 8 ++------
 1 file changed, 2 insertions(+), 6 deletions(-)

diff --git a/mm/khugepaged.c b/mm/khugepaged.c
index 941d1c7ea910..dd5a7d9bc593 100644
--- a/mm/khugepaged.c
+++ b/mm/khugepaged.c
@@ -1230,10 +1230,8 @@ static int collapse_huge_page(struct mm_struct *mm, unsigned long address,
 out_up_write:
 	mmap_write_unlock(mm);
 out_nolock:
-	if (hpage) {
-		mem_cgroup_uncharge(page_folio(hpage));
+	if (hpage)
 		put_page(hpage);
-	}
 	trace_mm_collapse_huge_page(mm, result == SCAN_SUCCEED, result);
 	return result;
 }
@@ -2250,10 +2248,8 @@ static int collapse_file(struct mm_struct *mm, unsigned long addr,
 		unlock_page(hpage);
 out:
 	VM_BUG_ON(!list_empty(&pagelist));
-	if (hpage) {
-		mem_cgroup_uncharge(page_folio(hpage));
+	if (hpage)
 		put_page(hpage);
-	}
 
 	trace_mm_khugepaged_collapse_file(mm, hpage, index, is_shmem, addr, file, nr, result);
 	return result;
-- 
2.39.1