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

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Date:   Thu, 8 Nov 2018 09:12:31 +0100
From:   Michal Hocko <mhocko@...nel.org>
To:     Anshuman Khandual <anshuman.khandual@....com>,
        Andrew Morton <akpm@...ux-foundation.org>
Cc:     linux-mm@...ck.org, Oscar Salvador <OSalvador@...e.com>,
        Baoquan He <bhe@...hat.com>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [RFC PATCH 5/5] mm, memory_hotplug: be more verbose for memory
 offline failures

On Thu 08-11-18 12:46:47, Anshuman Khandual wrote:
> 
> 
> On 11/07/2018 03:48 PM, Michal Hocko wrote:
[...]
> > @@ -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);
> 
> Seems like pr_warn() needs to have %d in here to print 'ret'.

Dohh. Rebase hickup. You are right ret:%d got lost on the way.

> Though
> dumping return code from migrate_pages() makes sense, wondering if
> it is required for each and every page which failed to migrate here
> or just one instance is enough.

Does it matter enough to special case one printk?

> > +				dump_page(page, NULL);
> > +			}
> 
> s/NULL/failed to migrate/ for dump_page().

Yes, makes sense.

> 
> >  			putback_movable_pages(&source);
> > +		}
> >  	}
> >  out:
> >  	return ret;
> > diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> > index a919ba5cb3c8..23267767bf98 100644
> > --- a/mm/page_alloc.c
> > +++ b/mm/page_alloc.c
> > @@ -7845,6 +7845,7 @@ bool has_unmovable_pages(struct zone *zone, struct page *page, int count,
> >  	return false;
> >  unmovable:
> >  	WARN_ON_ONCE(zone_idx(zone) == ZONE_MOVABLE);
> > +	dump_page(pfn_to_page(pfn+iter), "has_unmovable_pages");
> 
> s/has_unmovable_pages/is unmovable/

OK

> If we eally care about the function name, then dump_page() should be
> followed by dump_stack() like the case in some other instances.
>
> >  	return true;
> 
> This will be dumped from HugeTLB and CMA allocation paths as well through
> alloc_contig_range(). But it should be okay as those occurrences should be
> rare and dumping page state then will also help.

yes

Thanks and here is the incremental fix:

diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
index bf214beccda3..820397e18e59 100644
--- a/mm/memory_hotplug.c
+++ b/mm/memory_hotplug.c
@@ -1411,9 +1411,9 @@ do_migrate_range(unsigned long start_pfn, unsigned long end_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 ret:%d ",
 				       page_to_pfn(page), ret);
-				dump_page(page, NULL);
+				dump_page(page, "migration failure");
 			}
 			putback_movable_pages(&source);
 		}
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 23267767bf98..ec2c7916dc2d 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -7845,7 +7845,7 @@ bool has_unmovable_pages(struct zone *zone, struct page *page, int count,
 	return false;
 unmovable:
 	WARN_ON_ONCE(zone_idx(zone) == ZONE_MOVABLE);
-	dump_page(pfn_to_page(pfn+iter), "has_unmovable_pages");
+	dump_page(pfn_to_page(pfn+iter), "unmovable page");
 	return true;
 }
 
-- 
Michal Hocko
SUSE Labs