linux-kernel - Re : .... get_page_from_freelist : MInority Suggestion to accept GFP

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Date:	Mon, 6 Jul 2009 16:59:42 -0700
From:	Mitchell Erblich <erblichs@...thlink.net>
To:	Mitchell Erblich <erblichs@...thlink.net>
Cc:	David Rientjes <rientjes@...gle.com>, linux-kernel@...r.kernel.org
Subject: Re : .... get_page_from_freelist : MInority Suggestion to accept GFP_NOFAIL accept during boot

Group,

	Make plain text so vger.kernel.org will accept this..

	Mitchell Erblich
	====================

On Jul 6, 2009, at 4:56 PM, Mitchell Erblich wrote:

> David,
>
> 		The web page http://lkml.indiana.edu/hypermail/linux/kernel/
>
> 		Looking at the thread of emails on June 24 at 11:07:23
> 		upcoming kerneloops.org item: get_page_from_freelist
>
> 		We have code from Arjan de Van
>
> it's this warning in mm/page_alloc.c:
>
> * __GFP_NOFAIL is not to be used in new code.
> *
> * All __GFP_NOFAIL callers should be fixed so that they
> * properly detect and handle allocation failures.
> *
> * We most definitely don't want callers attempting to
> * allocate greater than single-page units with
> * __GFP_NOFAIL.
> */
> WARN_ON_ONCE(order > 0);
>
>
> 	Mitchell Erblich
> 	======================
> 		
> On Jul 3, 2009, at 2:01 AM, David Rientjes wrote:
>
>> On Thu, 2 Jul 2009, Mitchell Erblich wrote:
>>
>>> Group,
>>>
>>>
>>> 	If I may suggest a minority opinion about the depreciating of the
>>> GFP_NOFAIL flag..
>>>
>>> 	I saw no discussion on the acceptance of using this flag during  
>>> boot
>>> and shortly
>>> 	after boot.
>>>
>>> 	Many kernel structures require memory and thus should guarantee  
>>> memory
>>> 	before they continue.
>>> 	
>>> 	As Linux is moved within embedded environments with smaller  
>>> amounts of
>>> 	physical memory, the chance that earlier mem failures becomes  
>>> higher.
>>>
>>> 	For this logic alone, my minority opinion is to not depreciate the
>>> GFP_NOFAIL flag.
>>>
>>
>> I'm confused by your request because all allocations with orders  
>> under
>> PAGE_ALLOC_COSTLY_ORDER are inherently __GFP_NOFAIL and those that  
>> are not
>> can easily implement the same behavior in the caller:
>>
>> 	struct page *page;
>> 	do {
>> 		page = alloc_pages(...);
>> 	} while (!page);
>>
>> Hopefully something could be done to ensure the next call to  
>> alloc_pages()
>> would be more likely to succeed, but __GFP_NOFAIL doesn't provide  
>> that
>> anyway.
>

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