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Commit 79046ae0 authored by Andy Whitcroft's avatar Andy Whitcroft Committed by Linus Torvalds
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[PATCH] GFP_ZONETYPES: add commentry on how to calculate 



GFP_ZONETYPES define using GFP_ZONEMASK and add commentry

Add commentry explaining the optimisation that we can apply to GFP_ZONETYPES
when the leftmost bit is a 'loaner', it can only be set in isolation.

Signed-off-by: default avatarAndy Whitcroft <apw@shadowen.org>
Signed-off-by: default avatarAndrew Morton <akpm@osdl.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@osdl.org>
parent 42c722d4

include/linux/mmzone.h

+8 −0
Original line number Diff line number Diff line
@@ -91,6 +91,14 @@ struct per_cpu_pageset { 
 * be 8 (2 ** 3) zonelists.  GFP_ZONETYPES defines the number of possible

 * combinations of zone modifiers in "zone modifier space".

 *

 * As an optimisation any zone modifier bits which are only valid when

 * no other zone modifier bits are set (loners) should be placed in

 * the highest order bits of this field.  This allows us to reduce the

 * extent of the zonelists thus saving space.  For example in the case

 * of three zone modifier bits, we could require up to eight zonelists.

 * If the left most zone modifier is a "loner" then the highest valid

 * zonelist would be four allowing us to allocate only five zonelists.

 *

 * NOTE! Make sure this matches the zones in <linux/gfp.h>

 */

#define GFP_ZONEMASK	0x07