Re: [PATCH 4/5] mm, memory_hotplug: print reason for the offlining failure

Anshuman Khandual
2018-11-16T12:04:57Z

On 11/16/2018 02:00 PM, Michal Hocko wrote:
> From: Michal Hocko <mhocko@suse.com>
>
> The memory offlining failure reporting is inconsistent and insufficient.
> Some error paths simply do not report the failure to the log at all.
> When we do report there are no details about the reason of the failure
> and there are several of them which makes memory offlining failures
> hard to debug.
>
> Make sure that the
> memory offlining [mem %#010llx-%#010llx] failed
> message is printed for all failures and also provide a short textual
> reason for the failure e.g.
>
> [ 1984.506184] rac1 kernel: memory offlining [mem 0x82600000000-0x8267fffffff] failed due to signal backoff
>
> this tells us that the offlining has failed because of a signal pending
> aka user intervention.
>
> [akpm: tweak messages a bit]
> Signed-off-by: Michal Hocko <mhocko@suse.com>
> ---
> mm/memory_hotplug.c | 34 +++++++++++++++++++++++-----------
> 1 file changed, 23 insertions(+), 11 deletions(-)
>
> diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
> index a92b1b8f6218..88d50e74e3fe 100644
> --- a/mm/memory_hotplug.c
> +++ b/mm/memory_hotplug.c
> @@ -1553,6 +1553,7 @@ static int __ref __offline_pages(unsigned long start_pfn,
> unsigned long valid_start, valid_end;
> struct zone *zone;
> struct memory_notify arg;
> + char *reason;
>
> mem_hotplug_begin();
>
> @@ -1561,7 +1562,9 @@ static int __ref __offline_pages(unsigned long start_pfn,
> if (!test_pages_in_a_zone(start_pfn, end_pfn, &valid_start,
> &valid_end)) {
> mem_hotplug_done();
> - return -EINVAL;
> + ret = -EINVAL;
> + reason = "multizone range";
> + goto failed_removal;
> }
>
> zone = page_zone(pfn_to_page(valid_start));
> @@ -1573,7 +1576,8 @@ static int __ref __offline_pages(unsigned long start_pfn,
> MIGRATE_MOVABLE, true);
> if (ret) {
> mem_hotplug_done();
> - return ret;
> + reason = "failure to isolate range";
> + goto failed_removal;
> }
>
> arg.start_pfn = start_pfn;
> @@ -1582,15 +1586,19 @@ static int __ref __offline_pages(unsigned long start_pfn,
>
> ret = memory_notify(MEM_GOING_OFFLINE, &arg);
> ret = notifier_to_errno(ret);
> - if (ret)
> - goto failed_removal;
> + if (ret) {
> + reason = "notifier failure";
> + goto failed_removal_isolated;
> + }
>
> pfn = start_pfn;
> repeat:
> /* start memory hot removal */
> ret = -EINTR;
> - if (signal_pending(current))
> - goto failed_removal;
> + if (signal_pending(current)) {
> + reason = "signal backoff";
> + goto failed_removal_isolated;
> + }
>
> cond_resched();
> lru_add_drain_all();
> @@ -1607,8 +1615,10 @@ static int __ref __offline_pages(unsigned long start_pfn,
> * actually in order to make hugetlbfs's object counting consistent.
> */
> ret = dissolve_free_huge_pages(start_pfn, end_pfn);
> - if (ret)
> - goto failed_removal;
> + if (ret) {
> + reason = "failure to dissolve huge pages";
> + goto failed_removal_isolated;
> + }
> /* check again */
> offlined_pages = check_pages_isolated(start_pfn, end_pfn);
> if (offlined_pages < 0)
> @@ -1648,13 +1658,15 @@ static int __ref __offline_pages(unsigned long start_pfn,
> mem_hotplug_done();
> return 0;
>
> +failed_removal_isolated:
> + undo_isolate_page_range(start_pfn, end_pfn, MIGRATE_MOVABLE);
> failed_removal:
> - pr_debug("memory offlining [mem %#010llx-%#010llx] failed\n",
> + pr_debug("memory offlining [mem %#010llx-%#010llx] failed due to %s\n",
> (unsigned long long) start_pfn << PAGE_SHIFT,
> - ((unsigned long long) end_pfn << PAGE_SHIFT) - 1);
> + ((unsigned long long) end_pfn << PAGE_SHIFT) - 1,
> + reason);
> memory_notify(MEM_CANCEL_OFFLINE, &arg);
> /* pushback to free area */
> - undo_isolate_page_range(start_pfn, end_pfn, MIGRATE_MOVABLE);
> mem_hotplug_done();
> return ret;
> }
>

Reviewed-by: Anshuman Khandual <anshuman.khandual@arm.com>