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

[Andrew Morton <akpm@linux-foundation.org>]

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 a??KERN_SOHa??
 #define KERN_WARNING KERN_SOH "4" /* warning conditions */
                      ^~~~~~~~
./include/linux/printk.h:310:9: note: in expansion of macro a??KERN_WARNINGa??
  printk(KERN_WARNING pr_fmt(fmt), ##__VA_ARGS__)
         ^~~~~~~~~~~~
./include/linux/printk.h:311:17: note: in expansion of macro a??pr_warninga??
 #define pr_warn pr_warning
                 ^~~~~~~~~~
mm/memory_hotplug.c:1414:5: note: in expansion of macro a??pr_warna??
     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);
 			}