RE: Linux 5.19 __NR_move_pages failed for hugepage

["Wang, Haiyue" <haiyue.wang@intel.com>]

> -----Original Message-----
> From: Miaohe Lin <linmiaohe@huawei.com>
> Sent: Friday, August 12, 2022 09:59
> To: Wang, Haiyue <haiyue.wang@intel.com>
> Cc: akpm@linux-foundation.org; Linux-MM <linux-mm@kvack.org>; linux-kernel <linux-
> kernel@vger.kernel.org>; Naoya Horiguchi <naoya.horiguchi@linux.dev>; David Hildenbrand
> <david@redhat.com>
> 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@linux.dev/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.

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.

> 
> Thanks,
> Miaohe Lin
> 
> 
> >
> >
> >
> > BR,
> >
> > Haiyue
> >
> >
> >