linux-kernel - Re: [PATCH v2 3/3] mm/compaction: speed up pageblock_pfn_to

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Date:	Wed, 10 Feb 2016 10:58:45 -0800
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Vlastimil Babka <vbabka@...e.cz>
Cc:	Joonsoo Kim <js1304@...il.com>, Aaron Lu <aaron.lu@...el.com>,
	Mel Gorman <mgorman@...e.de>, Rik van Riel <riel@...hat.com>,
	David Rientjes <rientjes@...gle.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Linux Memory Management List <linux-mm@...ck.org>,
	Joonsoo Kim <iamjoonsoo.kim@....com>
Subject: Re: [PATCH v2 3/3] mm/compaction: speed up pageblock_pfn_to_page()
 when zone is contiguous

On Wed, 10 Feb 2016 14:42:57 +0100 Vlastimil Babka <vbabka@...e.cz> wrote:

> > --- a/mm/memory_hotplug.c
> > +++ b/mm/memory_hotplug.c
> > @@ -509,6 +509,8 @@ int __ref __add_pages(int nid, struct zone *zone, unsigned long phys_start_pfn,
> >  	int start_sec, end_sec;
> >  	struct vmem_altmap *altmap;
> >  
> > +	clear_zone_contiguous(zone);
> > +
> >  	/* during initialize mem_map, align hot-added range to section */
> >  	start_sec = pfn_to_section_nr(phys_start_pfn);
> >  	end_sec = pfn_to_section_nr(phys_start_pfn + nr_pages - 1);
> > @@ -540,6 +542,8 @@ int __ref __add_pages(int nid, struct zone *zone, unsigned long phys_start_pfn,
> >  	}
> >  	vmemmap_populate_print_last();
> >  
> > +	set_zone_contiguous(zone);
> > +
> >  	return err;
> >  }
> >  EXPORT_SYMBOL_GPL(__add_pages);
> 
> Between the clear and set, __add_pages() might return with -EINVAL,
> leaving the flag cleared potentially forever. Not critical, probably
> rare, but it should be possible to avoid this by moving the clear below
> the altmap check?

um, yes.  return-in-the-middle-of-a-function strikes again.

--- a/mm/memory_hotplug.c~mm-compaction-speed-up-pageblock_pfn_to_page-when-zone-is-contiguous-fix
+++ a/mm/memory_hotplug.c
@@ -526,7 +526,8 @@ int __ref __add_pages(int nid, struct zo
 		if (altmap->base_pfn != phys_start_pfn
 				|| vmem_altmap_offset(altmap) > nr_pages) {
 			pr_warn_once("memory add fail, invalid altmap\n");
-			return -EINVAL;
+			err = -EINVAL;
+			goto out;
 		}
 		altmap->alloc = 0;
 	}
@@ -544,9 +545,8 @@ int __ref __add_pages(int nid, struct zo
 		err = 0;
 	}
 	vmemmap_populate_print_last();
-
+out:
 	set_zone_contiguous(zone);
-
 	return err;
 }
 EXPORT_SYMBOL_GPL(__add_pages);
_