Page Size

When working with pages of memory, never assume the page size. It is a common mistake for x86 programmers to assume that the page size is 4KB. Although this is true on x86 machines, other architectures have different sizes. Some architectures support multiple page sizes, in fact! Table 19.4 lists each support architecture's valid page size(s).

Table 19.4. Architecture Page Size(s)

Architecture	PAGE_SHIFT	PAGE_SIZE
alpha	13	8KB
arm	12, 14, 15	4KB, 16KB, 32KB
cris	13	8KB
h8300	12	4KB
i386	12	4KB
ia64	12, 13, 14, 16	4KB, 8KB, 16KB, 64KB
m32r	12	4KB
m68k	12, 13	4KB, 8KB
m68knommu	12	4KB
mips	12	4KB
mips64	12	4KB
parisc	12	4KB
ppc	12	4KB
ppc64	12	4KB
s390	12	4KB
sh	12	4KB
sparc	12, 13	4KB, 8KB
sparc64	13	8KB
v850	12	4KB
x86_64	12	4KB

When working with pages of memory, use PAGE_SIZE as the size of a page, in bytes. The value PAGE_SHIFT is the number of bits to left-shift an address to get its page number. For example, on x86 with 4KB pages, PAGE_SIZE is 4096 and PAGE_SHIFT is 12. These vales are defined in <asm/page.h>.