Question

My kernel is

Linux localhost.localdomain 2.6.30 #5 SMP Tue Aug 10 00:56:36 CST 2010 x86_64 x86_64 x86_64 GNU/Linux

My kernel module find a 2M page while nr_hugepages is disabled.

 [root@localhost ~]# cat /proc/sys/vm/nr_hugepages
0

[root@localhost ~]# cat /proc/meminfo
...
Hugepagesize:       2048 kB
DirectMap4k:        9856 kB
DirectMap2M:     2052096 kB

I wonder whether linux64 kernel can have both 2M and 4K page together? And what’s the condition?

Answer 1

Yes. I believe you need to build with a special kernel setting in order to support huge page size, then allocate the #/huge pages you wish (the rest of memory will be regular, 4K pages).

Here’s are links:

• http://unixfoo.blogspot.com/2007/10/hugepages.html

• http://dbakerber.wordpress.com/2012/03/14/configuring-hugepages-for-oracle-on-linux/

• http://lwn.net/Articles/374424/