linux-kernel - Re: [RFC] propagate gfp_t to page table alloc functions

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Message-ID: <4F9DEA0C.8040203@kernel.org>
Date:	Mon, 30 Apr 2012 10:25:32 +0900
From:	Minchan Kim <minchan@...nel.org>
To:	David Rientjes <rientjes@...gle.com>
CC:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	Nick Piggin <npiggin@...il.com>,
	Ingo Molnar <mingo@...hat.com>, x86@...nel.org,
	Hugh Dickins <hughd@...gle.com>,
	Johannes Weiner <hannes@...xchg.org>,
	Rik van Riel <riel@...hat.com>, Mel Gorman <mgorman@...e.de>,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [RFC] propagate gfp_t to page table alloc functions

On 04/27/2012 07:43 PM, David Rientjes wrote:

> On Fri, 27 Apr 2012, Minchan Kim wrote:
> 
>>> Maybe a per-thread_info variant of gfp_allowed_mask?  So Andrew's 
>>> set_current_gfp() becomes set_current_gfp_allowed() that does
>>>
>>> 	void set_current_gfp_allowed(gfp_t gfp_mask)
>>> 	{
>>> 		current->gfp_allowed = gfp_mask & gfp_allowed_mask;
>>> 	}
>>>
>>> and then the page allocator does
>>>
>>> 	gfp_mask &= current->gfp_allowed;
>>>
>>> rather than how it currently does
>>>
>>> 	gfp_mask &= gfp_allowed_mask;
>>>
>>> and then the caller of set_current_gfp_allowed() cleans up with 
>>> set_current_gfp_allowed(__GFP_BITS_MASK).
>>
> 
> [trimmed the newsgroups from the reply, not sure what the point is?]
> 
>> Caller should restore old gfp_mask instead of __GFP_BITS_MASK in case of
>> nesting.And how do we care of atomic context?
>>
> 
> Eek, I'm hoping these aren't going to be nested but sure that seems 
> appropraite if they are.  (I'm also hoping these will only be either 
> __GFP_HIGH or __GFP_BITS_MASK and no other combinations.)
> 
> Forcing atomic context would just be set_current_gfp_allowed(__GFP_HIGH).


I mean it's not legal to access _current_ in atomic context so that
(gfp_mask &= current->gfp_allowed in page allocator) shouldn't.

-- 
Kind regards,
Minchan Kim
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