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

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Date:	Wed, 25 Apr 2012 17:20:32 -0700 (PDT)
From:	David Rientjes <rientjes@...gle.com>
To:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
cc:	Andrew Morton <akpm@...ux-foundation.org>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	Nick Piggin <npiggin@...il.com>,
	Minchan Kim <minchan@...nel.org>,
	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 Thu, 26 Apr 2012, KAMEZAWA Hiroyuki wrote:

> > Or do we instead do this:
> > 
> > -	some_function(foo, bar, GFP_NOIO);
> > +	old_gfp = set_current_gfp(GFP_NOIO);
> > +	some_function(foo, bar);
> > +	set_current_gfp(old_gfp);
> > 
> > So the rule is "if the code was using an explicit GFP_foo then convert
> > it to use set_current_gfp().  If the code was receiving a gfp_t
> > variable from the caller then delete that arg".
> > 
> > Or something like that.  It's all too hopelessly impractical to bother
> > discussing - 20 years too late!
> > 
> > 
> > otoh, maybe a constrained version of this could be used to address the
> > vmalloc() problem alone.
> > 
> 
> Yes, I think it will be good start.
> 

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).
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