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SubjectRe: [RFC PATCH 4/5] mm, memory_hotplug: print reason for the offlining failure
On Wed,  7 Nov 2018 11:18:29 +0100 Michal Hocko <mhocko@kernel.org> 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.
>
> ...

Some of these messages will come out looking a bit odd.

> @@ -1573,7 +1576,8 @@ static int __ref __offline_pages(unsigned long start_pfn,
> MIGRATE_MOVABLE, true);
> if (ret) {
> mem_hotplug_done();
> - return ret;
> + reason = "failed to isolate range";

"memory offlining [mem ...] failed due to failed 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 = "notifiers failure";

"memory offlining [mem ...] failed due to notifiers failure"

> @@ -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 = "fails to disolve hugetlb pages";

"memory offlining [mem ...] failed due to fails to disolve hugetlb pages"


Fix:

--- a/mm/memory_hotplug.c~mm-memory_hotplug-print-reason-for-the-offlining-failure-fix
+++ a/mm/memory_hotplug.c
@@ -1576,7 +1576,7 @@ static int __ref __offline_pages(unsigne
MIGRATE_MOVABLE, true);
if (ret) {
mem_hotplug_done();
- reason = "failed to isolate range";
+ reason = "failure to isolate range";
goto failed_removal
}

@@ -1587,7 +1587,7 @@ static int __ref __offline_pages(unsigne
ret = memory_notify(MEM_GOING_OFFLINE, &arg);
ret = notifier_to_errno(ret);
if (ret) {
- reason = "notifiers failure";
+ reason = "notifier failure";
goto failed_removal_isolated;
}

@@ -1616,7 +1616,7 @@ repeat:
*/
ret = dissolve_free_huge_pages(start_pfn, end_pfn);
if (ret) {
- reason = "fails to disolve hugetlb pages";
+ reason = "failure to dissolve huge pages";
goto failed_removal_isolated;
}
/* check again */
_
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