Re: [Patch v4 3/8] memory-hotplug: fix NR_FREE_PAGES mismatch

[Jianguo Wu]

On 2012/10/31 19:23, Wen Congyang wrote:
> NR_FREE_PAGES will be wrong after offlining pages.  We add/dec
> NR_FREE_PAGES like this now:
> 
> 1. move all pages in buddy system to MIGRATE_ISOLATE, and dec NR_FREE_PAGES
> 
> 2. don't add NR_FREE_PAGES when it is freed and the migratetype is
>    MIGRATE_ISOLATE
> 
> 3. dec NR_FREE_PAGES when offlining isolated pages.
> 
> 4. add NR_FREE_PAGES when undoing isolate pages.
> 
> When we come to step 3, all pages are in MIGRATE_ISOLATE list, and
> NR_FREE_PAGES are right.  When we come to step4, all pages are not in
> buddy system, so we don't change NR_FREE_PAGES in this step, but we change
> NR_FREE_PAGES in step3.  So NR_FREE_PAGES is wrong after offlining pages.
> So there is no need to change NR_FREE_PAGES in step3.
> 
> This patch also fixs a problem in step2: if the migratetype is
> MIGRATE_ISOLATE, we should not add NR_FRR_PAGES when we remove pages from
> pcppages.
> 
> Signed-off-by: Wen Congyang <wency@xxxxxxxxxxxxxx>
> Cc: David Rientjes <rientjes@xxxxxxxxxx>
> Cc: Jiang Liu <liuj97@xxxxxxxxx>
> Cc: Len Brown <len.brown@xxxxxxxxx>
> Cc: Benjamin Herrenschmidt <benh@xxxxxxxxxxxxxxxxxxx>
> Cc: Paul Mackerras <paulus@xxxxxxxxx>
> Cc: Christoph Lameter <cl@xxxxxxxxx>
> Cc: Minchan Kim <minchan.kim@xxxxxxxxx>
> Cc: KOSAKI Motohiro <kosaki.motohiro@xxxxxxxxxxxxxx>
> Cc: Yasuaki Ishimatsu <isimatu.yasuaki@xxxxxxxxxxxxxx>
> Cc: Dave Hansen <dave@xxxxxxxxxxxxxxxxxx>
> Cc: Mel Gorman <mel@xxxxxxxxx>
> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
> ---
>  mm/page_alloc.c | 10 +++++-----
>  1 file changed, 5 insertions(+), 5 deletions(-)
> 
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index 5b74de6..a7cd2d1 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -667,11 +667,13 @@ static void free_pcppages_bulk(struct zone *zone, int count,
>  			/* MIGRATE_MOVABLE list may include MIGRATE_RESERVEs */
>  			__free_one_page(page, zone, 0, mt);
>  			trace_mm_page_pcpu_drain(page, 0, mt);
> -			if (is_migrate_cma(mt))
> -				__mod_zone_page_state(zone, NR_FREE_CMA_PAGES, 1);
> +			if (likely(mt != MIGRATE_ISOLATE)) {

Hi Congyang,
	I think mt != MIGRATE_ISOLATE is always true here,
page from PCP's migratetype < MIGRATE_PCPTYPES.
When isolate page, we change pageblock's migratetype to MIGRATE_ISOLATE,
but set_freepage_migratetype() isn't called.
Maybe we can use mt = get_pageblock_migratetype() here ?

Thanks,
Jianguo Wu.

> +				__mod_zone_page_state(zone, NR_FREE_PAGES, 1);
> +				if (is_migrate_cma(mt))
> +					__mod_zone_page_state(zone, NR_FREE_CMA_PAGES, 1);
> +			}
>  		} while (--to_free && --batch_free && !list_empty(list));
>  	}
> -	__mod_zone_page_state(zone, NR_FREE_PAGES, count);
>  	spin_unlock(&zone->lock);
>  }
>  
> @@ -5987,8 +5989,6 @@ __offline_isolated_pages(unsigned long start_pfn, unsigned long end_pfn)
>  		list_del(&page->lru);
>  		rmv_page_order(page);
>  		zone->free_area[order].nr_free--;
> -		__mod_zone_page_state(zone, NR_FREE_PAGES,
> -				      - (1UL << order));
>  		for (i = 0; i < (1 << order); i++)
>  			SetPageReserved((page+i));
>  		pfn += (1 << order);
> 

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