linux-kernel - Re: [PATCH] mm: migrate: fix an incorrect call of prep_transhuge

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Date:   Wed, 22 Nov 2017 16:39:32 +0100
From:   Michal Hocko <mhocko@...nel.org>
To:     Zi Yan <zi.yan@...rutgers.edu>
Cc:     Zi Yan <zi.yan@...t.com>,
        Naoya Horiguchi <n-horiguchi@...jp.nec.com>,
        Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, Andrea Reale <ar@...ux.vnet.ibm.com>,
        Jérôme Glisse <jglisse@...hat.com>,
        stable@...r.kernel.org
Subject: Re: [PATCH] mm: migrate: fix an incorrect call of
 prep_transhuge_page()

On Wed 22-11-17 10:09:13, Zi Yan wrote:
> 
> 
> Michal Hocko wrote:
> > On Wed 22-11-17 09:43:46, Zi Yan wrote:
> >>
> >> Michal Hocko wrote:
[...]
> >>> but why is unsafe to enable the feature on other arches which support
> >>> THP? Is there any plan to do the next step and remove this config
> >>> option?
> >> Because different architectures have their own way of specifying a swap
> >> entry. This means, to support THP migration, each architecture needs to
> >> add its own __pmd_to_swp_entry() and __swp_entry_to_pmd(), which are
> >> used for arch-independent pmd_to_swp_entry() and swp_entry_to_pmd().
> > 
> > I understand that part. But this smells like a matter of coding, no?
> > I was suprised to see the note about safety which didn't make much sense
> > to me.
> 
> And testing as well. I had powerpc book3s support in my initial patch
> submission, but removed it because I do not have access to the powerpc
> machine any more. I also tried ARM64, which seems working by adding the
> code, but I have no hardware to test it now.
> 
> Any suggestions?

Cc arch maintainers and mailing lists?

-- 
Michal Hocko
SUSE Labs