Messages in this thread | | | Date | Wed, 18 Mar 2009 13:52:23 +0000 | From | Mel Gorman <> | Subject | Re: [PATCH 24/27] Convert gfp_zone() to use a table of precalculated values |
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On Mon, Mar 16, 2009 at 03:12:50PM -0400, Christoph Lameter wrote: > On Mon, 16 Mar 2009, Mel Gorman wrote: > > > +int gfp_zone_table[GFP_ZONEMASK] __read_mostly; > > The gfp_zone_table is compile time determinable. There is no need to > calculate it. >
The cost of calculating it is negligible and the code is then freed later in boot. Does having a const table make any difference?
> 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.
-- Mel Gorman Part-time Phd Student Linux Technology Center University of Limerick IBM Dublin Software Lab
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