linux-kernel - Re: [PATCH v6 1/2] mm: migration: fix the FOLL

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Date:   Wed, 17 Aug 2022 10:26:19 -0700
From:   Mike Kravetz <mike.kravetz@...cle.com>
To:     Andrew Morton <akpm@...ux-foundation.org>,
        Michael Ellerman <mpe@...erman.id.au>
Cc:     "Wang, Haiyue" <haiyue.wang@...el.com>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "david@...hat.com" <david@...hat.com>,
        "apopple@...dia.com" <apopple@...dia.com>,
        "linmiaohe@...wei.com" <linmiaohe@...wei.com>,
        "Huang, Ying" <ying.huang@...el.com>,
        "songmuchun@...edance.com" <songmuchun@...edance.com>,
        "naoya.horiguchi@...ux.dev" <naoya.horiguchi@...ux.dev>,
        "alex.sierra@....com" <alex.sierra@....com>,
        Heiko Carstens <hca@...ux.ibm.com>,
        Vasily Gorbik <gor@...ux.ibm.com>,
        Alexander Gordeev <agordeev@...ux.ibm.com>,
        Christian Borntraeger <borntraeger@...ux.ibm.com>,
        Sven Schnelle <svens@...ux.ibm.com>
Subject: Re: [PATCH v6 1/2] mm: migration: fix the FOLL_GET failure on
 following huge page

On 08/16/22 22:43, Andrew Morton wrote:
> On Wed, 17 Aug 2022 03:31:37 +0000 "Wang, Haiyue" <haiyue.wang@...el.com> wrote:
> 
> > > >  		}
> > > 
> > > I would be better to fix this for real at those three client code sites?
> > 
> > Then 5.19 will break for a while to wait for the final BIG patch ?
> 
> If that's the proposal then your [1/2] should have had a cc:stable and
> changelog words describing the plan for 6.0.
> 
> But before we do that I'd like to see at least a prototype of the final
> fixes to s390 and hugetlb, so we can assess those as preferable for
> backporting.  I don't think they'll be terribly intrusive or risky?

I will start on adding follow_huge_pgd() support.  Although, I may need
some help with verification from the powerpc folks, as that is the only
architecture which supports hugetlb pages at that level.

mpe any suggestions?

When Naoya recently modified follow_huge_pud, it ended up looking very
much like follow_huge_pmd (as it should).  I expect follow_huge_pgd
will be similar.  In the end we may want to factor out the common code.
However, for a backport it would be better to just modify follow_huge_pgd
and do the cleanup/condensing common code later.
-- 
Mike Kravetz