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

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Date:	Thu, 11 Feb 2016 10:58:26 +0900
From:	Joonsoo Kim <js1304@...il.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Vlastimil Babka <vbabka@...e.cz>, 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

2016-02-11 3:58 GMT+09:00 Andrew Morton <akpm@...ux-foundation.org>:
> 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);

Sorry for late response. I was on biggest holiday in Korea until now.
It seems that there is no issue left.
Andrew, Vlastimil, thanks for fixes and review.

Thanks.