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

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Message-ID: <alpine.DEB.2.00.1204270340450.11866@chino.kir.corp.google.com>
Date:	Fri, 27 Apr 2012 03:43:14 -0700 (PDT)
From:	David Rientjes <rientjes@...gle.com>
To:	Minchan Kim <minchan@...nel.org>
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 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).
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