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

From: Zi Yan
Date: Wed Apr 27 2022 - 17:05:06 EST

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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