linux-kernel - Re: [PATCH 6/9] mm/page_alloc: add informative debugging message in page_outside_zone

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Date:	Fri, 1 Feb 2013 16:28:48 -0800
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Cody P Schafer <cody@...ux.vnet.ibm.com>
Cc:	Linux MM <linux-mm@...ck.org>,
	David Hansen <dave@...ux.vnet.ibm.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Catalin Marinas <catalin.marinas@....com>
Subject: Re: [PATCH 6/9] mm/page_alloc: add informative debugging message in
 page_outside_zone_boundaries()

On Thu, 17 Jan 2013 14:52:58 -0800
Cody P Schafer <cody@...ux.vnet.ibm.com> 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 ]"
> 
> Signed-off-by: Cody P Schafer <cody@...ux.vnet.ibm.com>
> ---
>  mm/page_alloc.c | 7 +++++++
>  1 file changed, 7 insertions(+)
> 
> 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;
>  
>  	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;
>  }

As this condition leads to a VM_BUG_ON(), "pr_debug" seems rather wimpy
and I doubt if we need to be concerned about flooding the console.

I'll switch it to pr_err.

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