linux-kernel - Re: [PATCH] mm/hugetlb: Remove redundant VM_BUG_ON_PAGE on putback_active

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Date:   Mon, 8 Feb 2021 19:39:28 -0800
From:   Mike Kravetz <mike.kravetz@...cle.com>
To:     Miaohe Lin <linmiaohe@...wei.com>, akpm@...ux-foundation.org
Cc:     linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mm/hugetlb: Remove redundant VM_BUG_ON_PAGE on
 putback_active_hugepage()

On 2/8/21 6:10 PM, Miaohe Lin wrote:
> Hi:
> On 2021/2/9 9:26, Mike Kravetz wrote:
>> On 2/8/21 12:37 AM, Miaohe Lin wrote:
>>> PageHead(page) is implicitly checked in set_page_huge_active() via the
>>> PageHeadHuge(page) check. So remove this explicit one.
>>
>> I do not disagree with the code change.  However, this commit message
>> is not accurate.  set_page_huge_active() no longer exists in the tree
>> you are changing.  It was replaced with SetHPageMigratable.  Also, the
>> VM_BUG_ON_PAGE(!PageHeadHuge(page), page) was removed in the process.
>> So, there is no redundant check.
>>
>> However, a quick audit of calling code reveals that all callers know they
>> are operating on a hugetlb head page.
>>
> 
> So I should change the commit log like:
> 
> 	All callers know they are operating on a hugetlb head page. So this VM_BUG_ON_PAGE
> 	can't catch anything useful.
> 
> and send a v2. Right?

Correct,
-- 
Mike Kravetz