Get the page size

This page lists the different ways to get the kernel page size used in the device. To connect to the device, you can use adb.

$ adb shell

Use programming code

In C++, prefer getpagesize(2):

# include <unistd.h> ... ... = getpagesize();

In Java, you can use system config:

import android.system.Os; import android.system.OsConstants; ... = Os.sysconf(OsConstants._SC_PAGE_SIZE);

Use the getconf command

Use the getconf command to get the page size, shown as follows:

$ getconf PAGE_SIZE 4096

Use the /proc//smaps pseudo file

The KernelPageSize field in the pseudo file /proc/<pid>/smaps shows the page size, shown as follows:

$ grep KernelPageSize /proc/1/smaps KernelPageSize: 4 kB

Use the LD_SHOW_AUXV=1 linker flag

Use the LD_SHOW_AUXV flag to print the auxiliary vector of the program that is about to be executed. The AT_PAGESZ field contains the page size, shown as follows:

$ LD_SHOW_AUXV=1 ls AT_SYSINFO_EHDR 0x7250460000 AT_MINSIGSTKSZ 4720 AT_HWCAP 0b11111111111111111111111111111111 AT_PAGESZ 4096 AT_CLKTCK 100 AT_PHDR 0x5fda1e0040 AT_PHENT 56 AT_PHNUM 12 AT_BASE 0x72502f8000 AT_FLAGS 0 AT_ENTRY 0x5fda210000 AT_UID 0 AT_EUID 0 AT_GID 0 AT_EGID 0 AT_SECURE 0 AT_RANDOM 0x7fc59d66f8 AT_HWCAP2 0b100011001111111111 AT_EXECFN "/system/bin/ls" AT_PLATFORM "aarch64" data dev. init vendor

Use the /proc/config.gz pseudo file

Check the kernel configuration for the page size in the pseudo file /proc/config.gz. The possible configurations for the page size are:

  • CONFIG_ARM64_4K_PAGES=y: the kernel uses 4096-byte pages.
  • CONFIG_ARM64_16K_PAGES=y: the kernel uses 16384-byte pages.
  • CONFIG_ARM64_64K_PAGES=y: the kernel uses 65536-byte pages.
$ zcat /proc/config.gz | grep "CONFIG_ARM64_[164K]*_PAGES=y" CONFIG_ARM64_16K_PAGES=y

Use the auxiliary vector

When a program is executed, the kernel allocates and initializes the auxiliary vector with information, such as the page size, that is used by the dynamic linker. The auxiliary vector can be read from the pseudo file /proc/<pid>/auxv. The page size from the auxiliary vector of process 1 can be shown as follows:

$ od -N8 -j56 -td8 -An /proc/1/auxv 4096

Where:

  • od dumps files in hexadecimal, decimal or other formats.
  • -N8 -j56 dumps the 8 bytes starting at offset 56 into the file, corresponding to AT_PAGESZ.
  • -td8 formats the value as a decimal 8-byte integer.
  • -An causes just the value to be shown, not its address.

Read from a kernel image

You can read a kernel image's header to determine the page size. This is useful in the bootloader, if you need to know what type of kernel you're booting.

The page size is in the 25th byte of the kernel header:

 $ file Image Image: Linux kernel ARM64 boot executable Image, little-endian, 16K pages  $ hexdump -C Image -n 48 00000000 4d 5a 40 fa ff 7f 7b 14 00 00 00 00 00 00 00 00 |MZ@...{.........| 00000010 00 00 64 02 00 00 00 00 0c 00 00 00 00 00 00 00 |..d.............| 00000020 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 |................| 00000030

In this example, the value is 0x0C = 0000 1100b. Bit 1 has the value 0, and bit 2 has the value 1. Reading these two bits, we get 10b or 2 in decimal. Based on the value of these bits, you can determine the kernel page size:

  • 0 - Unspecified
  • 1 - 4 KB
  • 2 - 16 KB
  • 3 - 64 KB

For more information, see the Linux kernel documentation