Subject: [RFC 0/8] Reduce MAX_NR_ZONES and remove useless zones.
Newsgroups: gmane.linux.kernel
Date: 2006-07-03 21:55:34 GMT (3 years, 1 day, 4 hours and 44 minutes ago)
I keep seeing zones on various platforms that are never used and wonder why we compile support for them into the kernel. IA64 on SGI for example only uses ZONE_DMA other IA64 platforms can also use ZONE_NORMAL. So we have 50% useless zones. Large amounts of memory go to waste with systems with a few hundred nodes and a few hundred processors. My x86_64 system seems to only use ZONE_DMA and ZONE_DMA32. I never see pages in ZONE_NORMAL (probably because I have less than 4G memory). And ZONE_HIGHMEM on a 64 bit system? We can address all memory. I keep seeing all the highmem counters as zero on ia64 and x86_64 and even on i386 systems. Then it seems that ZONE_DMA32 is only used on x86_64 but we compile it into the kernel for all platforms. This patch makes ZONE_DMA32 and ZONE_HIGHMEM support optional. MAX_NR_ZONES will be 2 for most non i386 platforms and even for i386 without CONFIG_HIGHMEM set. I tested this on IA64 and x86_64. Compiles fine on i386 with and without CONFIG_HIGHMEM set. The patchset consists of 8 patches that are following this message. One could go even further than this patchset and also make ZONE_DMA optional because some platforms do not need a separate DMA zone and can do DMA to all of memory. This could reduce MAX_NR_ZONES to 1.