linux-kernel - Re: [PATCH 15/17] mm/page_alloc: add informative debugging message in page_outside_zone

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Message-ID: <50F603AC.90005@linux.vnet.ibm.com>
Date:	Tue, 15 Jan 2013 17:34:36 -0800
From:	Dave Hansen <dave@...ux.vnet.ibm.com>
To:	Cody P Schafer <cody@...ux.vnet.ibm.com>
CC:	Linux MM <linux-mm@...ck.org>, LKML <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Catalin Marinas <catalin.marinas@....com>
Subject: Re: [PATCH 15/17] mm/page_alloc: add informative debugging message
 in page_outside_zone_boundaries()

On 01/15/2013 04:24 PM, Cody P Schafer wrote:
> Add a debug message which prints when a page is found outside of the
> boundaries of the zone it should belong to. Format is:
> 	"page $pfn outside zone [ $start_pfn - $end_pfn ]"

I'd make sure to say 'pfn' here, just to make sure that it's explicitly
stated to be a pfn and not a 'struct page'

> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index f8ed277..f1783cf 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -239,13 +239,20 @@ static int page_outside_zone_boundaries(struct zone *zone, struct page *page)
>  	int ret = 0;
>  	unsigned seq;
>  	unsigned long pfn = page_to_pfn(page);
> +	unsigned long sp, start_pfn;

I think calling this zone_spanned is probably just fine.  Shouldn't take
up too much room.

>  	do {
>  		seq = zone_span_seqbegin(zone);
> +		start_pfn = zone->zone_start_pfn;
> +		sp = zone->spanned_pages;
>  		if (!zone_spans_pfn(zone, pfn))
>  			ret = 1;
>  	} while (zone_span_seqretry(zone, seq));
> 
> +	if (ret)
> +		pr_debug("page %lu outside zone [ %lu - %lu ]\n",
> +			pfn, start_pfn, start_pfn + sp);
> +
>  	return ret;
>  }

Is there a way we could also fit in something to disambiguate the zones?
 I can imagine a scenario where two zones might have identical
start/spanned_pages, so they might be impossible to tell apart in a
message like this.  Maybe we could add the NUMA node or the
DMA/Normal/Highmem text?

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