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KVA_PAGES is a compile time kernel option on the i386 architecture.

The default value is 256 (512 for PAE enabled kernels) and it is defined in i386/include/pmap.h. This option directly influences the size of the kernel virtual address space and how much is left for userland processes. A value of 256 (512 for PAE) divides the virtual address space (which has a size of 4GB on i386) into a chunk of 3GB for userspace programs (lower part) and 1GB for the kernel (upper part). 512 (1024 for PAE) divides the virtual address space into two 2GB parts. KVA_PAGES has to be a multiple of 4 (8 for PAE).

Warning
Setting KVA_PAGES to something different than the default may break some programs. Especially wine seems to be affected.