linux-kernel - [PATCH] mm: thp: remove redundant pgtable check in set_huge_zero

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Message-Id: <20220818082748.40021-1-zhengqi.arch@bytedance.com>
Date:   Thu, 18 Aug 2022 16:27:48 +0800
From:   Qi Zheng <zhengqi.arch@...edance.com>
To:     akpm@...ux-foundation.org
Cc:     linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        Qi Zheng <zhengqi.arch@...edance.com>
Subject: [PATCH] mm: thp: remove redundant pgtable check in set_huge_zero_page()

When the pgtable is NULL in the set_huge_zero_page(), we should
not increment the count of PTE page table pages by calling
mm_inc_nr_ptes(). Otherwise we may receive the following warning
when the mm exits:

	BUG: non-zero pgtables_bytes on freeing mm

Now we can't observe the above warning since only
do_huge_pmd_anonymous_page() invokes set_huge_zero_page() and the
pgtable can not be NULL.

Therefore, instead of moving mm_inc_nr_ptes() to the non-NULL
branch of pgtable, it is better to remove the redundant pgtable
check directly.

Signed-off-by: Qi Zheng <zhengqi.arch@...edance.com>
---
 mm/huge_memory.c | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index 83c47a989260..655da0b4fea0 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -770,8 +770,7 @@ static void set_huge_zero_page(pgtable_t pgtable, struct mm_struct *mm,
 		return;
 	entry = mk_pmd(zero_page, vma->vm_page_prot);
 	entry = pmd_mkhuge(entry);
-	if (pgtable)
-		pgtable_trans_huge_deposit(mm, pmd, pgtable);
+	pgtable_trans_huge_deposit(mm, pmd, pgtable);
 	set_pmd_at(mm, haddr, pmd, entry);
 	mm_inc_nr_ptes(mm);
 }
-- 
2.20.1