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SubjectRe: [RFC PATCH 5/5] mm, memory_hotplug: be more verbose for memory offline failures
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On 11/07/2018 03:48 PM, Michal Hocko wrote:
> From: Michal Hocko <mhocko@suse.com>
>
> There is only very limited information printed when the memory offlining
> fails:
> [ 1984.506184] rac1 kernel: memory offlining [mem 0x82600000000-0x8267fffffff] failed due to signal backoff
>
> This tells us that the failure is triggered by the userspace
> intervention but it doesn't tell us much more about the underlying
> reason. It might be that the page migration failes repeatedly and the
> userspace timeout expires and send a signal or it might be some of the
> earlier steps (isolation, memory notifier) takes too long.
>
> If the migration failes then it would be really helpful to see which
> page that and its state. The same applies to the isolation phase. If we
> fail to isolate a page from the allocator then knowing the state of the
> page would be helpful as well.
>
> Dump the page state that fails to get isolated or migrated. This will
> tell us more about the failure and what to focus on during debugging.
>
> Signed-off-by: Michal Hocko <mhocko@suse.com>
> ---
> mm/memory_hotplug.c | 12 ++++++++----
> mm/page_alloc.c | 1 +
> 2 files changed, 9 insertions(+), 4 deletions(-)
>
> diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
> index 1badac89c58e..bf214beccda3 100644
> --- a/mm/memory_hotplug.c
> +++ b/mm/memory_hotplug.c
> @@ -1388,10 +1388,8 @@ do_migrate_range(unsigned long start_pfn, unsigned long end_pfn)
> page_is_file_cache(page));
>
> } else {
> -#ifdef CONFIG_DEBUG_VM
> - pr_alert("failed to isolate pfn %lx\n", pfn);
> + pr_warn("failed to isolate pfn %lx\n", pfn)> dump_page(page, "isolation failed");
> -#endif
> put_page(page);
> /* Because we don't have big zone->lock. we should
> check this again here. */
> @@ -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'. 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.

> + dump_page(page, NULL);
> + }

s/NULL/failed to migrate/ for dump_page().

> 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/

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.

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