linux-kernel - Re: [PATCH V2] mm: fix kernel crash in khugepaged thread

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Message-ID: <20151105085033.GB7614@node.shutemov.name>
Date:	Thu, 5 Nov 2015 10:50:33 +0200
From:	"Kirill A. Shutemov" <kirill@...temov.name>
To:	Vlastimil Babka <vbabka@...e.cz>
Cc:	yalin wang <yalin.wang2010@...il.com>, akpm@...ux-foundation.org,
	kirill.shutemov@...ux.intel.com, jmarchan@...hat.com,
	mgorman@...hsingularity.net, ebru.akagunduz@...il.com,
	willy@...ux.intel.com, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH V2] mm: fix kernel crash in khugepaged thread

On Thu, Nov 05, 2015 at 09:12:34AM +0100, Vlastimil Babka wrote:
> On 10/29/2015 01:35 AM, Kirill A. Shutemov wrote:
> >> @@ -2605,9 +2603,9 @@ out_unmap:
> >>  		/* collapse_huge_page will return with the mmap_sem released */
> >>  		collapse_huge_page(mm, address, hpage, vma, node);
> >>  	}
> >> -out:
> >> -	trace_mm_khugepaged_scan_pmd(mm, page_to_pfn(page), writable, referenced,
> >> -				     none_or_zero, result, unmapped);
> >> +	trace_mm_khugepaged_scan_pmd(mm, pte_present(pteval) ?
> >> +			pte_pfn(pteval) : -1, writable, referenced,
> >> +			none_or_zero, result, unmapped);
> > 
> > maybe passing down pte instead of pfn?
> 
> Maybe just pass the page, and have tracepoint's fast assign check for !NULL and
> do page_to_pfn itself? That way the complexity and overhead is only in the
> tracepoint and when enabled.

Agreed.

-- 
 Kirill A. Shutemov
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