linux-kernel - Re: [PATCH v4 2/3] mm/page_alloc.c: add config option to sanitize freed pages

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Date:	Wed, 20 May 2015 14:27:37 +0200
From:	Anisse Astier <anisse@...ier.eu>
To:	yalin wang <yalin.wang2010@...il.com>
Cc:	Pavel Machek <pavel@....cz>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Mel Gorman <mgorman@...e.de>,
	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
	David Rientjes <rientjes@...gle.com>,
	Alan Cox <gnomes@...rguk.ukuu.org.uk>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Peter Zijlstra <peterz@...radead.org>,
	PaX Team <pageexec@...email.hu>,
	Brad Spengler <spender@...ecurity.net>,
	Kees Cook <keescook@...omium.org>,
	Andi Kleen <andi@...stfloor.org>,
	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	Len Brown <len.brown@...el.com>, linux-mm@...ck.org,
	Linux PM list <linux-pm@...r.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v4 2/3] mm/page_alloc.c: add config option to sanitize
 freed pages

On Tue, May 19, 2015 at 3:58 AM, yalin wang <yalin.wang2010@...il.com> wrote:
> 2015-05-18 21:04 GMT+08:00 Anisse Astier <anisse@...ier.eu>:
>> On Mon, May 18, 2015 at 3:02 PM, Pavel Machek <pavel@....cz> wrote:
>>>
>>> Ok. So there is class of errors where this helps, but you are not
>>> aware of any such errors in kernel, so you can't fix them... Right?
>>
>> Correct.
>> --
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> i feel your patch is the same as CONFIG_DEBUG_PAGEALLOC ,
> the difference is that CONFIG_DEBUG_PAGEALLOC  will clear
> page to a magic number, while your patch will
> clear to zero,
> do we really need this duplicated function ?

It's different because DEBUG_PAGEALLOC will only use page poisoning on
certain architectures, and clearing a page to a magic number doesn't
allow to optimize alloc with _GFP_ZERO.

Regards,

Anisse
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