linux-kernel - Re: [PATCH 4/6] mm/vmstat: add zone range overlapping check

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Date:	Wed, 23 Mar 2016 15:47:46 +0100
From:	Vlastimil Babka <vbabka@...e.cz>
To:	js1304@...il.com, Andrew Morton <akpm@...ux-foundation.org>
Cc:	Rik van Riel <riel@...hat.com>,
	Johannes Weiner <hannes@...xchg.org>,
	Mel Gorman <mgorman@...e.de>,
	Laura Abbott <lauraa@...eaurora.org>,
	Minchan Kim <minchan@...nel.org>,
	Marek Szyprowski <m.szyprowski@...sung.com>,
	Michal Nazarewicz <mina86@...a86.com>,
	"Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>,
	linux-mm@...ck.org, linux-kernel@...r.kernel.org,
	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	Joonsoo Kim <iamjoonsoo.kim@....com>
Subject: Re: [PATCH 4/6] mm/vmstat: add zone range overlapping check

On 03/14/2016 08:31 AM, js1304@...il.com wrote:
> From: Joonsoo Kim <iamjoonsoo.kim@....com>
>
> There is a system that node's pfn are overlapped like as following.
>
> -----pfn-------->
> N0 N1 N2 N0 N1 N2
>
> Therefore, we need to care this overlapping when iterating pfn range.
>
> There are two places in vmstat.c that iterates pfn range and
> they don't consider this overlapping. Add it.
>
> Without this patch, above system could over count pageblock number
> on a zone.
>
> Signed-off-by: Joonsoo Kim <iamjoonsoo.kim@....com>
> ---
>   mm/vmstat.c | 7 +++++++
>   1 file changed, 7 insertions(+)
>
> diff --git a/mm/vmstat.c b/mm/vmstat.c
> index 5e43004..0a726e3 100644
> --- a/mm/vmstat.c
> +++ b/mm/vmstat.c
> @@ -1010,6 +1010,9 @@ static void pagetypeinfo_showblockcount_print(struct seq_file *m,
>   		if (!memmap_valid_within(pfn, page, zone))
>   			continue;

The above already does this for each page within the block, but it's 
guarded by CONFIG_ARCH_HAS_HOLES_MEMORYMODEL. I guess that's not the 
case of your system, right?

I guess your added check should go above this, though. Also what about 
employing pageblock_pfn_to_page() here and in all other applicable 
places, so it's unified and optimized by zone->contiguous?

>
> +		if (page_zone(page) != zone)
> +			continue;
> +
>   		mtype = get_pageblock_migratetype(page);
>
>   		if (mtype < MIGRATE_TYPES)
> @@ -1076,6 +1079,10 @@ static void pagetypeinfo_showmixedcount_print(struct seq_file *m,
>   				continue;
>
>   			page = pfn_to_page(pfn);
> +
> +			if (page_zone(page) != zone)
> +				continue;
> +
>   			if (PageBuddy(page)) {
>   				pfn += (1UL << page_order(page)) - 1;
>   				continue;
>