diff options
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 93a849f742d..88c30f844ab 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 |