On Wed, 7 Nov 2018 11:18:30 +0100 Michal Hocko <mhocko@xxxxxxxxxx> wrote:
> From: Michal Hocko <mhocko@xxxxxxxx>
>
> 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.
>
> ...
>
> --- 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);
> + dump_page(page, NULL);
> + }
./include/linux/kern_levels.h:5:18: warning: too many arguments for format [-Wformat-extra-args]
#define KERN_SOH "\001" /* ASCII Start Of Header */
^
./include/linux/kern_levels.h:12:22: note: in expansion of macro ‘KERN_SOH’
#define KERN_WARNING KERN_SOH "4" /* warning conditions */
^~~~~~~~
./include/linux/printk.h:310:9: note: in expansion of macro ‘KERN_WARNING’
printk(KERN_WARNING pr_fmt(fmt), ##__VA_ARGS__)
^~~~~~~~~~~~
./include/linux/printk.h:311:17: note: in expansion of macro ‘pr_warning’
#define pr_warn pr_warning
^~~~~~~~~~
mm/memory_hotplug.c:1414:5: note: in expansion of macro ‘pr_warn’
pr_warn("migrating pfn %lx failed ",
^~~~~~~
--- a/mm/memory_hotplug.c~mm-memory_hotplug-be-more-verbose-for-memory-offline-failures-fix
+++ a/mm/memory_hotplug.c
@@ -1411,7 +1411,7 @@ do_migrate_range(unsigned long start_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: %d",
page_to_pfn(page), ret);
dump_page(page, NULL);
}
