RE: Linux 5.19 __NR_move_pages failed for hugepage

[Wang, Haiyue]

> -----Original Message-----
> From: Miaohe Lin <linmiaohe@xxxxxxxxxx>
> Sent: Friday, August 12, 2022 14:41
> To: Wang, Haiyue <haiyue.wang@xxxxxxxxx>
> Cc: akpm@xxxxxxxxxxxxxxxxxxxx; Linux-MM <linux-mm@xxxxxxxxx>; linux-kernel <linux-
> kernel@xxxxxxxxxxxxxxx>; Naoya Horiguchi <naoya.horiguchi@xxxxxxxxx>; David Hildenbrand
> <david@xxxxxxxxxx>
> Subject: Re: Linux 5.19 __NR_move_pages failed for hugepage
> 
> On 2022/8/12 11:04, Wang, Haiyue wrote:
> >> -----Original Message-----
> >> From: Miaohe Lin <linmiaohe@xxxxxxxxxx>
> >> Sent: Friday, August 12, 2022 09:59
> >> To: Wang, Haiyue <haiyue.wang@xxxxxxxxx>
> >> Cc: akpm@xxxxxxxxxxxxxxxxxxxx; Linux-MM <linux-mm@xxxxxxxxx>; linux-kernel <linux-
> >> kernel@xxxxxxxxxxxxxxx>; Naoya Horiguchi <naoya.horiguchi@xxxxxxxxx>; David Hildenbrand
> >> <david@xxxxxxxxxx>
> >> Subject: Re: Linux 5.19 __NR_move_pages failed for hugepage
> >>
> >> On 2022/8/11 16:01, Wang, Haiyue wrote:
> >>> Hi Miaohe,
> >>>
> >>>
> >>
> >> Hi Haiyue,
> >>
> >> Many thanks for your report and debug.
> >>
> >>>
> >>> When I call "*syscall (__NR_move_pages, 0, n_pages, ptr, 0, status, 0)*" to get the huge page node
> >>>
> >>> information, it is failed with '-2' returned in 'status' array.
> >>>
> >>>
> >>>
> >>> After some debug, I found that "*follow_huge_pud*" will return NULL if '*FOLL_GET*' is set.
> >>>
> >>>
> >>
> https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=e66f17ff71772b209eed39de
> >> 35aaa99ba819c93d
> >>
> <https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=e66f17ff71772b209eed39d
> >> e35aaa99ba819c93d>
> >>>
> >>>
> >>>
> >>> This will make your patch doesn't work for huge page.
> >>>
> >>>
> >>
> https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=4cd614841c06338a087769ee
> >> 3cfa96718784d1f5
> >>
> <https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=4cd614841c06338a087769e
> >> e3cfa96718784d1f5>
> >>>
> >>
> >> Supporting of '*FOLL_GET*' in follow_huge_pud is introduced via the below commit:
> >>
> >> https://lore.kernel.org/all/20220714042420.1847125-9-
> >> naoya.horiguchi@xxxxxxxxx/T/#mb3c83df087fba454b7b4ea32227fb8775ca70081
> >>
> >> But that's still not perfect yet. For s390 version of follow_huge_pud, FOLL_GET is still not
> supported.
> >> And pgd level
> >> hugepage doesn't support FOLL_GET now.
> >>
> >>>
> >>>
> >>> Not sure you know this issue or not, just share my debug information.
> >>
> >> I'm not sure whether it's better to revert my above "problematic" patch first then add it back when
> >> all hugetlb pages support FOLL_GET.
> >> Or we could just live with it? Any thoughts?
> >>
> >
> > TBH, the issue is more complicated than I think. :-(
> >
> > Looks like only '[PATCH v7 5/8] mm, hwpoison: set PG_hwpoison for busy hugetlb pages' will be
> > backported to 5.19 ? Only this patch has "Fixes:" tag. If so, it will break 5.19.
> 
> If you want to mitigate the problem of __NR_move_pages failing for hugepage, "[PATCH v7 2/8]
> mm/hugetlb:
> make pud_huge() and follow_huge_pud() aware of non-present pud entry" could be backported to 5.19.
> 
> >
> > I just run VPP 'https://fd.io/' to find the error message about huge page allocation
> > after I switched from 5.18 to 5.19.
> 
> Do you mean the reported problem is found by VPP? Anyway, you can send a patch to fix the problem if
> you like. :)
> I will try fixing it if requested of course (but I'm not sure how to fix it yet).
> 

I try a quick fix, and cc'ed you. Ugly design, but your fix is kept.

> Thanks,
> Miaohe Lin