linux-kernel - Re: [PATCH v7 1/2] mm: migration: fix the FOLL

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Date:   Thu, 25 Aug 2022 19:53:12 -0700
From:   Andrew Morton <akpm@...ux-foundation.org>
To:     Gerald Schaefer <gerald.schaefer@...ux.ibm.com>
Cc:     Haiyue Wang <haiyue.wang@...el.com>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, david@...hat.com, apopple@...dia.com,
        linmiaohe@...wei.com, ying.huang@...el.com,
        songmuchun@...edance.com, naoya.horiguchi@...ux.dev,
        alex.sierra@....com, mike.kravetz@...cle.com,
        Baolin Wang <baolin.wang@...ux.alibaba.com>,
        Heiko Carstens <hca@...ux.ibm.com>,
        Vasily Gorbik <gor@...ux.ibm.com>,
        Alexander Gordeev <agordeev@...ux.ibm.com>
Subject: Re: [PATCH v7 1/2] mm: migration: fix the FOLL_GET failure on
 following huge page

On Thu, 25 Aug 2022 14:39:17 +0200 Gerald Schaefer <gerald.schaefer@...ux.ibm.com> wrote:

> On Wed, 24 Aug 2022 11:38:58 -0700
> Andrew Morton <akpm@...ux-foundation.org> wrote:
> 
> > On Tue, 23 Aug 2022 21:58:40 +0800 Haiyue Wang <haiyue.wang@...el.com> wrote:
> > 
> > > Not all huge page APIs support FOLL_GET option, so move_pages() syscall
> > > will fail to get the page node information for some huge pages.
> > > 
> > > Like x86 on linux 5.19 with 1GB huge page API follow_huge_pud(), it will
> > > return NULL page for FOLL_GET when calling move_pages() syscall with the
> > > NULL 'nodes' parameter, the 'status' parameter has '-2' error in array.
> > > 
> > > Note: follow_huge_pud() now supports FOLL_GET in linux 6.0.
> > >       Link: https://lore.kernel.org/all/20220714042420.1847125-3-naoya.horiguchi@linux.dev
> > > 
> > > But these huge page APIs don't support FOLL_GET:
> > >   1. follow_huge_pud() in arch/s390/mm/hugetlbpage.c
> > >   2. follow_huge_addr() in arch/ia64/mm/hugetlbpage.c
> > >      It will cause WARN_ON_ONCE for FOLL_GET.
> > >   3. follow_huge_pgd() in mm/hugetlb.c
> > 
> > What happened to the proposal to fix these three sites so this patch is
> > not needed?
> 
> For s390, you can add my patch from
> https://lore.kernel.org/linux-mm/20220818135717.609eef8a@thinkpad/
> to this series.
> 

Thanks, I added that.