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From:   Zi Yan <ziy@nvidia.com>
To:     Qian Cai <quic_qiancai@quicinc.com>
Cc:     David Hildenbrand <david@redhat.com>, linux-mm@kvack.org,
        linux-kernel@vger.kernel.org,
        virtualization@lists.linux-foundation.org,
        Vlastimil Babka <vbabka@suse.cz>,
        Mel Gorman <mgorman@techsingularity.net>,
        Eric Ren <renzhengeek@gmail.com>,
        Mike Rapoport <rppt@kernel.org>,
        Oscar Salvador <osalvador@suse.de>,
        Christophe Leroy <christophe.leroy@csgroup.eu>,
        Andrew Morton <akpm@linux-foundation.org>
Subject: Re: [PATCH v11 0/6] Use pageblock_order for cma and alloc_contig_range alignment.
Date:   Thu, 19 May 2022 17:35:15 -0400
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On 19 May 2022, at 16:57, Qian Cai wrote:

> On Thu, Apr 28, 2022 at 08:39:06AM -0400, Zi Yan wrote:
>> How about the one attached? I can apply it to next-20220428. Let me kn=
ow
>> if you are using a different branch. Thanks.
>
> Zi, it turns out that the endless loop in isolate_single_pageblock() ca=
n
> still be reproduced on today's linux-next tree by running the reproduce=
r a
> few times. With this debug patch applied, it keeps printing the same
> values.
>
> --- a/mm/page_isolation.c
> +++ b/mm/page_isolation.c
> @@ -399,6 +399,8 @@ static int isolate_single_pageblock(unsigned long b=
oundary_pfn, gfp_t gfp_flags,
>                                 };
>                                 INIT_LIST_HEAD(&cc.migratepages);
>
> +                               printk_ratelimited("KK stucked pfn=3D%l=
u head_pfn=3D%lu nr_pages=3D%lu boundary_pfn=3D%lu\n", pfn, head_pfn, nr_=
pages, boundary_pfn);
>                                 ret =3D __alloc_contig_migrate_range(&c=
c, head_pfn,
>                                                         head_pfn + nr_p=
ages);
>
>  isolate_single_pageblock: 179 callbacks suppressed
>  KK stucked pfn=3D2151120384 head_pfn=3D2151120384 nr_pages=3D512 bound=
ary_pfn=3D2151120896
>  KK stucked pfn=3D2151120384 head_pfn=3D2151120384 nr_pages=3D512 bound=
ary_pfn=3D2151120896
>  KK stucked pfn=3D2151120384 head_pfn=3D2151120384 nr_pages=3D512 bound=
ary_pfn=3D2151120896
>  KK stucked pfn=3D2151120384 head_pfn=3D2151120384 nr_pages=3D512 bound=
ary_pfn=3D2151120896
>  KK stucked pfn=3D2151120384 head_pfn=3D2151120384 nr_pages=3D512 bound=
ary_pfn=3D2151120896
>  KK stucked pfn=3D2151120384 head_pfn=3D2151120384 nr_pages=3D512 bound=
ary_pfn=3D2151120896
>  KK stucked pfn=3D2151120384 head_pfn=3D2151120384 nr_pages=3D512 bound=
ary_pfn=3D2151120896
>  KK stucked pfn=3D2151120384 head_pfn=3D2151120384 nr_pages=3D512 bound=
ary_pfn=3D2151120896
>  KK stucked pfn=3D2151120384 head_pfn=3D2151120384 nr_pages=3D512 bound=
ary_pfn=3D2151120896
>  KK stucked pfn=3D2151120384 head_pfn=3D2151120384 nr_pages=3D512 bound=
ary_pfn=3D2151120896

Hi Qian,

Thanks for your testing.

Do you have a complete reproducer? From your printout, it is clear that a=
 512-page compound
page caused the infinite loop, because the page was not migrated and the =
code kept
retrying. But __alloc_contig_migrate_range() is supposed to return non-ze=
ro to tell the
code the page cannot be migrated and the code will goto failed without re=
trying. It will be
great you can share what exactly has run after boot, so that I can reprod=
uce locally to
identify what makes __alloc_contig_migrate_range() return 0 without migra=
ting the page.

Can you also try the patch below to see if it fixes the infinite loop?

diff --git a/mm/page_isolation.c b/mm/page_isolation.c
index b3f074d1682e..abde1877bbcb 100644
--- a/mm/page_isolation.c
+++ b/mm/page_isolation.c
@@ -417,10 +417,9 @@ static int isolate_single_pageblock(unsigned long bo=
undary_pfn, gfp_t gfp_flags,
                                order =3D 0;
                                outer_pfn =3D pfn;
                                while (!PageBuddy(pfn_to_page(outer_pfn))=
) {
-                                       if (++order >=3D MAX_ORDER) {
-                                               outer_pfn =3D pfn;
-                                               break;
-                                       }
+                                       /* abort if the free page cannot =
be found */
+                                       if (++order >=3D MAX_ORDER)
+                                               goto failed;
                                        outer_pfn &=3D ~0UL << order;
                                }
                                pfn =3D outer_pfn;

--
Best Regards,
Yan, Zi

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