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| author | Andy Whitcroft <apw@shadowen.org> | 2006-02-01 03:05:26 -0800 |
|---|---|---|
| committer | Linus Torvalds <torvalds@g5.osdl.org> | 2006-02-01 08:53:14 -0800 |
| commit | 79046ae07ae21245520ca0aab985ee6678a879f8 (patch) | |
| tree | 8a980747ab9eeaa3407e2aa2366a4c6e95dee9d0 /include/linux/mmzone.h | |
| parent | 42c722d4cb4022e56ff200f3f5a58c0dfd7edac6 (diff) | |
| download | lwn-79046ae07ae21245520ca0aab985ee6678a879f8.tar.gz lwn-79046ae07ae21245520ca0aab985ee6678a879f8.zip | |
[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: Andy Whitcroft <apw@shadowen.org>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
Diffstat (limited to 'include/linux/mmzone.h')
| -rw-r--r-- | include/linux/mmzone.h | 8 |
1 files changed, 8 insertions, 0 deletions
diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h index 93a849f742db..88c30f844abf 100644 --- a/include/linux/mmzone.h +++ b/include/linux/mmzone.h @@ -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 |