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

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Date:   Tue, 9 Feb 2021 10:10:00 +0800
From:   Miaohe Lin <linmiaohe@...wei.com>
To:     Mike Kravetz <mike.kravetz@...cle.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()

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?