Re: [PATCH v7 1/2] mm: migration: fix the FOLL_GET failure on following huge page

[Andrew Morton]

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

> On Wed, 24 Aug 2022 11:38:58 -0700
> Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> wrote:
> 
> > On Tue, 23 Aug 2022 21:58:40 +0800 Haiyue Wang <haiyue.wang@xxxxxxxxx> 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@xxxxxxxxx
> > > 
> > > 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.