Re: [RFC PATCH 5/5] mm, memory_hotplug: be more verbose for memory offline failures

[Michal Hocko <mhocko@kernel.org>]

On Thu 15-11-18 16:07:16, Andrew Morton wrote:
> On Wed,  7 Nov 2018 11:18:30 +0100 Michal Hocko <mhocko@kernel.org> 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.
> > 
> > ...
> >
> > --- 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 ",
>      ^~~~~~~

yeah, 0day already complained and I've posted a follow up fix
http://lkml.kernel.org/r/20181108081231.GN27423@dhcp22.suse.cz

Let me post a version 2 with all the fixups.
 
Thanks!

> --- 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);
>  			}
> 

-- 
Michal Hocko
SUSE Labs