linux-kernel - Re: [PATCH 12/25] Remove a branch by assuming __GFP_HIGH == ALLOC

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Date:	Tue, 21 Apr 2009 13:25:50 +0300
From:	Pekka Enberg <penberg@...helsinki.fi>
To:	Mel Gorman <mel@....ul.ie>
Cc:	Linux Memory Management List <linux-mm@...ck.org>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	Christoph Lameter <cl@...ux-foundation.org>,
	Nick Piggin <npiggin@...e.de>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Lin Ming <ming.m.lin@...el.com>,
	Zhang Yanmin <yanmin_zhang@...ux.intel.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH 12/25] Remove a branch by assuming __GFP_HIGH == 
	ALLOC_HIGH

Hi Mel,

On Tue, Apr 21, 2009 at 11:45 AM, Mel Gorman <mel@....ul.ie> wrote:
>> > @@ -1639,8 +1639,8 @@ gfp_to_alloc_flags(gfp_t gfp_mask)
>> >      * policy or is asking for __GFP_HIGH memory.  GFP_ATOMIC requests will
>> >      * set both ALLOC_HARDER (!wait) and ALLOC_HIGH (__GFP_HIGH).
>> >      */
>> > -   if (gfp_mask & __GFP_HIGH)
>> > -           alloc_flags |= ALLOC_HIGH;
>> > +   VM_BUG_ON(__GFP_HIGH != ALLOC_HIGH);
>> > +   alloc_flags |= (gfp_mask & __GFP_HIGH);
>>
>> Shouldn't you then also change ALLOC_HIGH to use __GFP_HIGH or at least
>> add a comment somewhere?
>
> That might break in weird ways if __GFP_HIGH changes in value then. I
> can add a comment though
>
> /*
>  * __GFP_HIGH is assumed to be the same as ALLOC_HIGH to save a branch.
>  * Check for DEBUG_VM that the assumption is still correct. It cannot be
>  * checked at compile-time due to casting
>  */
>
> ?

I'm perfectly fine with something like that.

Reviewed-by: Pekka Enberg <penberg@...helsinki.fi>

                                      Pekka
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