linux-kernel - [PATCH 4/5] khugepaged: remove unnecessary mem_cgroup_uncharge() in collapse_[file|huge

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Date:   Thu, 4 Mar 2021 07:30:12 -0500
From:   Miaohe Lin <linmiaohe@...wei.com>
To:     <akpm@...ux-foundation.org>
CC:     <riel@...hat.com>, <kirill.shutemov@...ux.intel.com>,
        <ebru.akagunduz@...il.com>, <dan.carpenter@...cle.com>,
        <linux-kernel@...r.kernel.org>, <linux-mm@...ck.org>,
        <linmiaohe@...wei.com>
Subject: [PATCH 4/5] khugepaged: remove unnecessary mem_cgroup_uncharge() in collapse_[file|huge_page]

Since commit 7ae88534cdd9 ("mm: move mem_cgroup_uncharge out of
__page_cache_release()"), the mem_cgroup will be uncharged when hpage is
freed. Uncharge mem_cgroup here is harmless but it looks confusing and
buggy: if mem_cgroup charge failed, we will call mem_cgroup_uncharge()
uncorrectly in error path because hpage is not IS_ERR_OR_NULL().

Signed-off-by: Miaohe Lin <linmiaohe@...wei.com>
---
 mm/khugepaged.c | 4 ----
 1 file changed, 4 deletions(-)

diff --git a/mm/khugepaged.c b/mm/khugepaged.c
index e886a8618c33..68579cdbdc9b 100644
--- a/mm/khugepaged.c
+++ b/mm/khugepaged.c
@@ -1211,8 +1211,6 @@ static void collapse_huge_page(struct mm_struct *mm,
 out_up_write:
 	mmap_write_unlock(mm);
 out_nolock:
-	if (!IS_ERR_OR_NULL(*hpage))
-		mem_cgroup_uncharge(*hpage);
 	trace_mm_collapse_huge_page(mm, isolated, result);
 	return;
 out:
@@ -1968,8 +1966,6 @@ static void collapse_file(struct mm_struct *mm,
 	unlock_page(new_page);
 out:
 	VM_BUG_ON(!list_empty(&pagelist));
-	if (!IS_ERR_OR_NULL(*hpage))
-		mem_cgroup_uncharge(*hpage);
 	/* TODO: tracepoints */
 }
 
-- 
2.19.1