Re: [PATCH v11 0/6] Use pageblock_order for cma and alloc_contig_range alignment.

[Zi Yan <ziy@nvidia.com>]

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On 27 Apr 2022, at 9:30, Zi Yan wrote:

> On 27 Apr 2022, at 9:27, Qian Cai wrote:
>
>> On Tue, Apr 26, 2022 at 05:38:58PM -0400, Zi Yan wrote:
>>> Thanks. Do you mind attaching your config file? I cannot reproduce
>>> the deadlock locally using my own config. I also see kmemleak_scan
>>> in the dumped stack, so it must be something else in addition to
>>> memory online/offline causing the issue.
>>
>> Actually, it is one of those *offline* operations, i.e.,
>>
>> echo 0 > /sys/devices/system/memory/memoryNNN/online
>>
>> looping forever which never finish after more than 2-hour.
>
> Thank you for the detailed information. I am able to reproduce the
> issue locally. I will update the patch once I fix the bug.

Hi Qian,

Do you mind checking if the patch below fixes the issue? It works
for me.

The original code was trying to migrate non-migratible compound pages
(high-order slab pages from my tests) during isolation and caused
an infinite loop. The patch avoids non-migratible pages.

I will update my patch series once we confirm the patch fixes
the bug.

Thanks.

diff --git a/mm/page_isolation.c b/mm/page_isolation.c
index 75e454f5cf45..c39980fce626 100644
--- a/mm/page_isolation.c
+++ b/mm/page_isolation.c
@@ -367,58 +367,68 @@ static int isolate_single_pageblock(unsigned long boundary_pfn, gfp_t gfp_flags,
                }
                /*
                 * migrate compound pages then let the free page handling code
-                * above do the rest. If migration is not enabled, just fail.
+                * above do the rest. If migration is not possible, just fail.
                 */
-               if (PageHuge(page) || PageTransCompound(page)) {
-#if defined CONFIG_COMPACTION || defined CONFIG_CMA
+               if (PageCompound(page)) {
                        unsigned long nr_pages = compound_nr(page);
-                       int order = compound_order(page);
                        struct page *head = compound_head(page);
                        unsigned long head_pfn = page_to_pfn(head);
-                       int ret;
-                       struct compact_control cc = {
-                               .nr_migratepages = 0,
-                               .order = -1,
-                               .zone = page_zone(pfn_to_page(head_pfn)),
-                               .mode = MIGRATE_SYNC,
-                               .ignore_skip_hint = true,
-                               .no_set_skip_hint = true,
-                               .gfp_mask = gfp_flags,
-                               .alloc_contig = true,
-                       };
-                       INIT_LIST_HEAD(&cc.migratepages);

                        if (head_pfn + nr_pages < boundary_pfn) {
-                               pfn += nr_pages;
+                               pfn = head_pfn + nr_pages;
                                continue;
                        }

-                       ret = __alloc_contig_migrate_range(&cc, head_pfn,
-                                               head_pfn + nr_pages);
-
-                       if (ret)
-                               goto failed;
+#if defined CONFIG_MIGRATION
                        /*
-                        * reset pfn, let the free page handling code above
-                        * split the free page to the right migratetype list.
-                        *
-                        * head_pfn is not used here as a hugetlb page order
-                        * can be bigger than MAX_ORDER-1, but after it is
-                        * freed, the free page order is not. Use pfn within
-                        * the range to find the head of the free page and
-                        * reset order to 0 if a hugetlb page with
-                        * >MAX_ORDER-1 order is encountered.
+                        * hugetlb, lru compound (THP), and movable compound pages
+                        * can be migrated. Otherwise, fail the isolation.
                         */
-                       if (order > MAX_ORDER-1)
+                       if (PageHuge(page) || PageLRU(page) || __PageMovable(page)) {
+                               int order;
+                               unsigned long outer_pfn;
+                               int ret;
+                               struct compact_control cc = {
+                                       .nr_migratepages = 0,
+                                       .order = -1,
+                                       .zone = page_zone(pfn_to_page(head_pfn)),
+                                       .mode = MIGRATE_SYNC,
+                                       .ignore_skip_hint = true,
+                                       .no_set_skip_hint = true,
+                                       .gfp_mask = gfp_flags,
+                                       .alloc_contig = true,
+                               };
+                               INIT_LIST_HEAD(&cc.migratepages);
+
+                               ret = __alloc_contig_migrate_range(&cc, head_pfn,
+                                                       head_pfn + nr_pages);
+
+                               if (ret)
+                                       goto failed;
+                               /*
+                                * reset pfn to the head of the free page, so
+                                * that the free page handling code above can split
+                                * the free page to the right migratetype list.
+                                *
+                                * head_pfn is not used here as a hugetlb page order
+                                * can be bigger than MAX_ORDER-1, but after it is
+                                * freed, the free page order is not. Use pfn within
+                                * the range to find the head of the free page.
+                                */
                                order = 0;
-                       while (!PageBuddy(pfn_to_page(pfn))) {
-                               order++;
-                               pfn &= ~0UL << order;
-                       }
-                       continue;
-#else
-                       goto failed;
+                               outer_pfn = pfn;
+                               while (!PageBuddy(pfn_to_page(outer_pfn))) {
+                                       if (++order >= MAX_ORDER) {
+                                               outer_pfn = pfn;
+                                               break;
+                                       }
+                                       outer_pfn &= ~0UL << order;
+                               }
+                               pfn = outer_pfn;
+                               continue;
+                       } else
 #endif
+                               goto failed;
                }

                pfn++;
--
Best Regards,
Yan, Zi

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