+ mm-thp-remove-redundant-pgtable-check-in-set_huge_zero_page.patch added to mm-unstable branch

[Andrew Morton <akpm@linux-foundation.org>]

The patch titled
     Subject: mm: thp: remove redundant pgtable check in set_huge_zero_page()
has been added to the -mm mm-unstable branch.  Its filename is
     mm-thp-remove-redundant-pgtable-check-in-set_huge_zero_page.patch

This patch will shortly appear at
     https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-thp-remove-redundant-pgtable-check-in-set_huge_zero_page.patch

This patch will later appear in the mm-unstable branch at
    git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

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------------------------------------------------------
From: Qi Zheng <zhengqi.arch@bytedance.com>
Subject: mm: thp: remove redundant pgtable check in set_huge_zero_page()
Date: Thu, 18 Aug 2022 16:27:48 +0800

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.

Link: https://lkml.kernel.org/r/20220818082748.40021-1-zhengqi.arch@bytedance.com
Signed-off-by: Qi Zheng <zhengqi.arch@bytedance.com>
Cc: Mike Kravetz <mike.kravetz@oracle.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 mm/huge_memory.c |    3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

--- a/mm/huge_memory.c~mm-thp-remove-redundant-pgtable-check-in-set_huge_zero_page
+++ a/mm/huge_memory.c
@@ -771,8 +771,7 @@ static void set_huge_zero_page(pgtable_t
 		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);
 }
_

Patches currently in -mm which might be from zhengqi.arch@bytedance.com are

mm-thp-remove-redundant-pgtable-check-in-set_huge_zero_page.patch