linux-kernel - Re: [RFC PATCH v2 01/16] mm,hwpoison: cleanup unused PageHuge() check

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Date:   Mon, 21 Oct 2019 14:16:36 +0200
From:   Michal Hocko <mhocko@...nel.org>
To:     Naoya Horiguchi <n-horiguchi@...jp.nec.com>
Cc:     Oscar Salvador <osalvador@...e.de>,
        "mike.kravetz@...cle.com" <mike.kravetz@...cle.com>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [RFC PATCH v2 01/16] mm,hwpoison: cleanup unused PageHuge() check

On Mon 21-10-19 07:00:46, Naoya Horiguchi wrote:
> On Fri, Oct 18, 2019 at 01:48:32PM +0200, Michal Hocko wrote:
> > On Thu 17-10-19 16:21:08, Oscar Salvador wrote:
> > > From: Naoya Horiguchi <n-horiguchi@...jp.nec.com>
> > > 
> > > Drop the PageHuge check since memory_failure forks into memory_failure_hugetlb()
> > > for hugetlb pages.
> > > 
> > > Signed-off-by: Oscar Salvador <osalvador@...e.de>
> > > Signed-off-by: Naoya Horiguchi <n-horiguchi@...jp.nec.com>
> > 
> > s-o-b chain is reversed.
> > 
> > The code is a bit confusing. Doesn't this check aim for THP?
> 
> No, PageHuge() is false for thp, so this if branch is just dead code.
> 
> > AFAICS
> > PageTransHuge(hpage) will split the THP or fail so PageTransHuge
> > shouldn't be possible anymore, right?
> 
> Yes, that's right.
> 
> > But why does hwpoison_user_mappings
> > still work with hpage then?
> 
> hwpoison_user_mappings() is called both from memory_failure() and
> from memory_failure_hugetlb(), so it need handle both cases.

Thanks for the clarification. Maybe the changelog could be more explicit
because the code is quite confusing.
-- 
Michal Hocko
SUSE Labs