linux-kernel - Re: [PATCH V4] mm: fix kernel crash in khugepaged thread

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Date:	Fri, 13 Nov 2015 18:24:24 +0800
From:	yalin wang <yalin.wang2010@...il.com>
To:	Hillf Danton <hillf.zj@...baba-inc.com>
Cc:	Steven Rostedt <rostedt@...dmis.org>,
	Ingo Molnar <mingo@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Rik van Riel <riel@...hat.com>,
	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
	Vlastimil Babka <vbabka@...e.cz>, Mel Gorman <mgorman@...e.de>,
	linux-kernel <linux-kernel@...r.kernel.org>, linux-mm@...ck.org
Subject: Re: [PATCH V4] mm: fix kernel crash in khugepaged thread


> On Nov 13, 2015, at 16:41, Hillf Danton <hillf.zj@...baba-inc.com> wrote:
> 
>> 
>> Instead of the condition, we could have:
>> 
>> 	__entry->pfn = page ? page_to_pfn(page) : -1;
>> 
>> 
>> But if there's no reason to do the tracepoint if page is NULL, then
>> this patch is fine. I'm just throwing out this idea.
>> 
> we trace only if page is valid
> 
> --- linux-next/mm/huge_memory.c	Fri Nov 13 16:00:22 2015
> +++ b/mm/huge_memory.c	Fri Nov 13 16:26:19 2015
> @@ -1987,7 +1987,8 @@ static int __collapse_huge_page_isolate(
> 
> out:
> 	release_pte_pages(pte, _pte);
> -	trace_mm_collapse_huge_page_isolate(page_to_pfn(page), none_or_zero,
> +	if (page)
> +		trace_mm_collapse_huge_page_isolate(page_to_pfn(page), none_or_zero,
> 					    referenced, writable, result);
> 	return 0;
> }
> —
> 
my V4  patch move  if (!page)  into trace function,
so that we don’t need call page_to_fn()  if the trace if disabled .
more efficient  .
Thanks


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