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SubjectRe: [RFC PATCH 5/5] mm, memory_hotplug: be more verbose for memory offline failures
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On 11/08/2018 01:42 PM, Michal Hocko wrote:
> On Thu 08-11-18 12:46:47, Anshuman Khandual wrote:
>>
>>
>> On 11/07/2018 03:48 PM, Michal Hocko wrote:
> [...]
>>> @@ -1411,8 +1409,14 @@ do_migrate_range(unsigned long start_pfn, unsigned long end_pfn)
>>> /* Allocate a new page from the nearest neighbor node */
>>> ret = migrate_pages(&source, new_node_page, NULL, 0,
>>> MIGRATE_SYNC, MR_MEMORY_HOTPLUG);
>>> - if (ret)
>>> + if (ret) {
>>> + list_for_each_entry(page, &source, lru) {
>>> + pr_warn("migrating pfn %lx failed ",
>>> + page_to_pfn(page), ret);
>>
>> Seems like pr_warn() needs to have %d in here to print 'ret'.
>
> Dohh. Rebase hickup. You are right ret:%d got lost on the way.
>
>> Though
>> dumping return code from migrate_pages() makes sense, wondering if
>> it is required for each and every page which failed to migrate here
>> or just one instance is enough.
>
> Does it matter enough to special case one printk?
I just imagined how a bunch of prints will look like when multiple pages
failed to migrate probably for the same reason. But I guess its okay.

>
>>> + dump_page(page, NULL);
>>> + }
>>
>> s/NULL/failed to migrate/ for dump_page().
>
> Yes, makes sense.
>
>>
>>> putback_movable_pages(&source);
>>> + }
>>> }
>>> out:
>>> return ret;
>>> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
>>> index a919ba5cb3c8..23267767bf98 100644
>>> --- a/mm/page_alloc.c
>>> +++ b/mm/page_alloc.c
>>> @@ -7845,6 +7845,7 @@ bool has_unmovable_pages(struct zone *zone, struct page *page, int count,
>>> return false;
>>> unmovable:
>>> WARN_ON_ONCE(zone_idx(zone) == ZONE_MOVABLE);
>>> + dump_page(pfn_to_page(pfn+iter), "has_unmovable_pages");
>>
>> s/has_unmovable_pages/is unmovable/
>
> OK
>
>> If we eally care about the function name, then dump_page() should be
>> followed by dump_stack() like the case in some other instances.
>>
>>> return true;
>>
>> This will be dumped from HugeTLB and CMA allocation paths as well through
>> alloc_contig_range(). But it should be okay as those occurrences should be
>> rare and dumping page state then will also help.
>
> yes
>
> Thanks and here is the incremental fix:
>
> diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
> index bf214beccda3..820397e18e59 100644
> --- a/mm/memory_hotplug.c
> +++ b/mm/memory_hotplug.c
> @@ -1411,9 +1411,9 @@ do_migrate_range(unsigned long start_pfn, unsigned long end_pfn)
> MIGRATE_SYNC, MR_MEMORY_HOTPLUG);
> if (ret) {
> list_for_each_entry(page, &source, lru) {
> - pr_warn("migrating pfn %lx failed ",
> + pr_warn("migrating pfn %lx failed ret:%d ",
> page_to_pfn(page), ret);
> - dump_page(page, NULL);
> + dump_page(page, "migration failure");
> }
> putback_movable_pages(&source);
> }
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index 23267767bf98..ec2c7916dc2d 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -7845,7 +7845,7 @@ bool has_unmovable_pages(struct zone *zone, struct page *page, int count,
> return false;
> unmovable:
> WARN_ON_ONCE(zone_idx(zone) == ZONE_MOVABLE);
> - dump_page(pfn_to_page(pfn+iter), "has_unmovable_pages");
> + dump_page(pfn_to_page(pfn+iter), "unmovable page");
> return true;
> }

It looks good.

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