linux-kernel - Re: [PATCH 24/27] Convert gfp_zone() to use a table of precalculated values

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Date:	Wed, 18 Mar 2009 13:21:30 -0400 (EDT)
From:	Christoph Lameter <cl@...ux-foundation.org>
To:	Mel Gorman <mel@....ul.ie>
cc:	Linux Memory Management List <linux-mm@...ck.org>,
	Pekka Enberg <penberg@...helsinki.fi>,
	Rik van Riel <riel@...hat.com>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	Johannes Weiner <hannes@...xchg.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>
Subject: Re: [PATCH 24/27] Convert gfp_zone() to use a table of precalculated
 values



> time.
>
> > > > const int gfp_zone_table[GFP_ZONEMASK] = {
> > > > 	ZONE_NORMAL,		/* 00 No flags set */
> > > > 	ZONE_DMA,		/* 01 Only GFP_DMA set */
> > > > 	ZONE_HIGHMEM,		/* 02 Only GFP_HIGHMEM set */
> > > > 	ZONE_DMA,		/* 03 GFP_HIGHMEM and GFP_DMA set */
> > > > 	ZONE_DMA32,		/* 04 Only GFP_DMA32 set */
> > > > 	ZONE_DMA,		/* 05 GFP_DMA and GFP_DMA32 set */
> > > > 	ZONE_DMA32,		/* 06 GFP_DMA32 and GFP_HIGHMEM set */
> > > > 	ZONE_DMA,		/* 07 GFP_DMA, GFP_DMA32 and GFP_DMA32 set */
> > > > 	ZONE_MOVABLE,		/* 08 Only ZONE_MOVABLE set */
> > > > 	ZONE_DMA,		/* 09 MOVABLE + DMA */
> > > > 	ZONE_MOVABLE,		/* 0A MOVABLE + HIGHMEM */
> > > > 	ZONE_DMA,		/* 0B MOVABLE + DMA + HIGHMEM */
> > > > 	ZONE_DMA32,		/* 0C MOVABLE + DMA32 */
> > > > 	ZONE_DMA,		/* 0D MOVABLE + DMA + DMA32 */
> > > > 	ZONE_DMA32,		/* 0E MOVABLE + DMA32 + HIGHMEM */
> > > > 	ZONE_DMA		/* 0F MOVABLE + DMA32 + HIGHMEM + DMA
> > > > };
> > > >
> > > > Hmmmm... Guess one would need to add some #ifdeffery here to setup
> > > > ZONE_NORMAL in cases there is no DMA, DMA32 and HIGHMEM.
> > > >
> > >
> > > Indeed, as I said, this is somewhat error prone which is why the patch
> > > calculates the table at run-time instead of compile-time trickery.
> >
> > One would need to define some macros to make it simpler I guess
> >
> > Write something like
> >
> > #ifdef CONFIG_ZONE_DMA
> > #define TZONE_DMA ZONE_DMA
> > #else
> > #define TZONE_DMA ZONE_NORMAL
> > #endif
> >
> > for each configurable item. Then just add the T to the above table.
> >
>
> If you don't mind, I'd like to postpone writing such a patch until a second
> or third pass at improving the allocator. I don't think I'll have the time
> in the short-term to put together a const-initialised-table patch that will
> definitily be correct.
>
> Alternatively, I can drop this patch entirely from the set.
>
>

Let me give it a shot:

Note that there is a slight buggyness in the current implementation of
gfp_zone. If you set both GFP_DMA32 and GFP_HIGHMEM and the arch does not
support GFP_DMA32 then gfp_zone returns GFP_HIGHMEM which may result in
memory being allocated that cannot be used for I/O.

This version here returns GFP_NORMAL which is more correct.


#ifdef CONFIG_ZONE_HIGHMEM
#define OPT_ZONE_HIGHMEM ZONE_HIGHMEM
#else
#define OPT_ZONE_HIGHMEM ZONE_NORMAL
#endif

#ifdef CONFIG_ZONE_DMA
#define OPT_ZONE_DMA ZONE_DMA
#else
#define OPT_ZONE_DMA ZONE_NORMAL
#endif

#ifdef CONFIG_ZONE_DMA32
#define OPT_ZONE_DMA32 ZONE_DMA32
#else
#define OPT_ZONE_DMA32 OPT_ZONE_DMA
#endif


const int gfp_zone_table[GFP_ZONEMASK] = {
	ZONE_NORMAL,            /* 00 No flags set */
	OPT_ZONE_DMA,           /* 01 GFP_DMA */
	OPT_ZONE_HIGHMEM,       /* 02 GFP_HIGHMEM */
        OPT_ZONE_DMA,           /* 03 GFP_HIGHMEM GFP_DMA */
        OPT_ZONE_DMA32,         /* 04 GFP_DMA32 */
        OPT_ZONE_DMA,           /* 05 GFP_DMA32 GFP_DMA */
        OPT_ZONE_DMA32,         /* 06 GFP_DMA32 GFP_HIGHMEM */
        OPT_ZONE_DMA,           /* 07 GFP_DMA32 GFP_HIGHMEM GFP_DMA */
        ZONE_NORMAL,            /* 08 ZONE_MOVABLE */
        OPT_ZONE_DMA,           /* 09 MOVABLE + DMA */
        ZONE_MOVABLE,           /* 0A MOVABLE + HIGHMEM */
        OPT_ZONE_DMA,           /* 0B MOVABLE + HIGHMEM + DMA */
        OPT_ZONE_DMA32,         /* 0C MOVABLE + DMA32 */
        OPT_ZONE_DMA,           /* 0D MOVABLE + DMA32 + DMA */
        OPT_ZONE_DMA32,         /* 0E MOVABLE + DMA32 + HIGHMEM */
        OPT_ZONE_DMA            /* 0F MOVABLE + DMA32 + HIGHMEM + DMA */
};

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