PROBLEM: Doesn't compile without CONFIG_SWAP

["haael" <haael@interia.pl>]

I was compiling Linux 2.6.5 with -mjb1 patch, trying to get as small kernel as 
possible. I got an error:
<code>
  CC      mm/vmscan.o
mm/vmscan.c: In function `refill_inactive_zone':
mm/vmscan.c:650: `swapper_space' undeclared (first use in this function)
mm/vmscan.c:650: (Each undeclared identifier is reported only once
mm/vmscan.c:650: for each function it appears in.)
make[1]: *** [mm/vmscan.o] B??d 1
make: *** [mm] Błąd 2
</code>

I had changed the file mm/vmscan.c at line 649 from:
<code>
		app_centile = 100 - ((i.freeram + get_page_cache_size() -
			swapper_space.nrpages) / (i.totalram / 100));
</code>
to:
<code>
#ifdef CONFIG_SWAP
		app_centile = 100 - ((i.freeram + get_page_cache_size() -
			swapper_space.nrpages) / (i.totalram / 100));
#else /* CONFIG_SWAP */
		app_centile = 100 - ((i.freeram + get_page_cache_size()) / (i.totalram / 
100));
#endif /* CONFIG_SWAP */
<code>
Then it compiled (and even worked).

My config was:
<code>
#
# Automatically generated make config: don't edit
#
CONFIG_X86=y
CONFIG_MMU=y
CONFIG_UID16=y
CONFIG_GENERIC_ISA_DMA=y

#
# Code maturity level options
#
CONFIG_EXPERIMENTAL=y
CONFIG_CLEAN_COMPILE=y
# CONFIG_STANDALONE is not set
CONFIG_BROKEN_ON_SMP=y

#
# General setup
#
# CONFIG_SWAP is not set
# CONFIG_SYSVIPC is not set
# CONFIG_BSD_PROCESS_ACCT is not set
# CONFIG_SYSCTL is not set
CONFIG_LOG_BUF_SHIFT=14
# CONFIG_HOTPLUG is not set
# CONFIG_IKCONFIG is not set
CONFIG_EMBEDDED=y
# CONFIG_KALLSYMS is not set
CONFIG_FUTEX=y
CONFIG_EPOLL=y
# CONFIG_IOSCHED_NOOP is not set
# CONFIG_IOSCHED_AS is not set
CONFIG_IOSCHED_DEADLINE=y
CONFIG_CC_OPTIMIZE_FOR_SIZE=y

#
# Loadable module support
#
# CONFIG_MODULES is not set

#
# Processor type and features
#
CONFIG_X86_PC=y
# CONFIG_X86_ELAN is not set
# CONFIG_X86_VOYAGER is not set
# CONFIG_X86_NUMAQ is not set
# CONFIG_X86_SUMMIT is not set
# CONFIG_X86_BIGSMP is not set
# CONFIG_X86_VISWS is not set
# CONFIG_X86_GENERICARCH is not set
# CONFIG_X86_ES7000 is not set
CONFIG_M386=y
# CONFIG_M486 is not set
# CONFIG_M586 is not set
# CONFIG_M586TSC is not set
# CONFIG_M586MMX is not set
# CONFIG_M686 is not set
# CONFIG_MPENTIUMII is not set
# CONFIG_MPENTIUMIII is not set
# CONFIG_MPENTIUMM is not set
# CONFIG_MPENTIUM4 is not set
# CONFIG_MK6 is not set
# CONFIG_MK7 is not set
# CONFIG_MK8 is not set
# CONFIG_MCRUSOE is not set
# CONFIG_MWINCHIPC6 is not set
# CONFIG_MWINCHIP2 is not set
# CONFIG_MWINCHIP3D is not set
# CONFIG_MCYRIXIII is not set
# CONFIG_MVIAC3_2 is not set
CONFIG_X86_GENERIC=y
CONFIG_X86_L1_CACHE_SHIFT=7
CONFIG_RWSEM_GENERIC_SPINLOCK=y
CONFIG_X86_PPRO_FENCE=y
CONFIG_X86_F00F_BUG=y
CONFIG_X86_INTEL_USERCOPY=y
# CONFIG_X86_4G is not set
# CONFIG_X86_SWITCH_PAGETABLES is not set
# CONFIG_X86_4G_VM_LAYOUT is not set
# CONFIG_X86_UACCESS_INDIRECT is not set
# CONFIG_X86_HIGH_ENTRY is not set
# CONFIG_HPET_TIMER is not set
# CONFIG_HPET_EMULATE_RTC is not set
# CONFIG_VSYSCALL_GTOD is not set
# CONFIG_SMP is not set
# CONFIG_X86_UP_APIC is not set
# CONFIG_X86_MCE is not set
# CONFIG_TOSHIBA is not set
# CONFIG_I8K is not set
# CONFIG_MICROCODE is not set
# CONFIG_X86_MSR is not set
# CONFIG_X86_CPUID is not set

#
# Firmware Drivers
#
# CONFIG_EDD is not set
CONFIG_NOHIGHMEM=y
# CONFIG_HIGHMEM4G is not set
# CONFIG_HIGHMEM64G is not set
# CONFIG_MATH_EMULATION is not set
# CONFIG_MTRR is not set
CONFIG_100HZ=y
# CONFIG_1000HZ is not set
# CONFIG_REGPARM is not set
CONFIG_KEXEC=y

#
# Power management options (ACPI, APM)
#
# CONFIG_PM is not set

#
# ACPI (Advanced Configuration and Power Interface) Support
#
# CONFIG_ACPI is not set

#
# CPU Frequency scaling
#
# CONFIG_CPU_FREQ is not set

#
# Bus options (PCI, PCMCIA, EISA, MCA, ISA)
#
CONFIG_PCI=y
# CONFIG_PCI_GOBIOS is not set
# CONFIG_PCI_GOMMCONFIG is not set
CONFIG_PCI_GODIRECT=y
# CONFIG_PCI_GOANY is not set
CONFIG_PCI_DIRECT=y
# CONFIG_PCI_LEGACY_PROC is not set
# CONFIG_PCI_NAMES is not set
CONFIG_ISA=y
# CONFIG_EISA is not set
# CONFIG_MCA is not set
# CONFIG_SCx200 is not set

#
# Executable file formats
#
CONFIG_BINFMT_ELF=y
# CONFIG_BINFMT_AOUT is not set
# CONFIG_BINFMT_MISC is not set

#
# Device Drivers
#

#
# Generic Driver Options
#

#
# Memory Technology Devices (MTD)
#
# CONFIG_MTD is not set

#
# Parallel port support
#
# CONFIG_PARPORT is not set

#
# Plug and Play support
#
# CONFIG_PNP is not set

#
# Block devices
#
# CONFIG_BLK_DEV_FD is not set
# CONFIG_BLK_DEV_XD is not set
# CONFIG_BLK_CPQ_DA is not set
# CONFIG_BLK_CPQ_CISS_DA is not set
# CONFIG_BLK_DEV_DAC960 is not set
# CONFIG_BLK_DEV_UMEM is not set
# CONFIG_BLK_DEV_LOOP is not set
# CONFIG_BLK_DEV_CARMEL is not set
CONFIG_BLK_DEV_RAM=y
CONFIG_BLK_DEV_RAM_SIZE=4096
CONFIG_BLK_DEV_INITRD=y
# CONFIG_LBD is not set

#
# ATA/ATAPI/MFM/RLL support
#
CONFIG_IDE=y
CONFIG_BLK_DEV_IDE=y

#
# Please see Documentation/ide.txt for help/info on IDE drives
#
# CONFIG_BLK_DEV_HD_IDE is not set
CONFIG_BLK_DEV_IDEDISK=y
# CONFIG_IDEDISK_MULTI_MODE is not set
# CONFIG_IDEDISK_STROKE is not set
# CONFIG_BLK_DEV_IDECD is not set
# CONFIG_BLK_DEV_IDETAPE is not set
# CONFIG_BLK_DEV_IDEFLOPPY is not set
# CONFIG_IDE_TASK_IOCTL is not set
# CONFIG_IDE_TASKFILE_IO is not set

#
# IDE chipset support/bugfixes
#
CONFIG_IDE_GENERIC=y
# CONFIG_BLK_DEV_CMD640 is not set
# CONFIG_BLK_DEV_IDEPCI is not set
# CONFIG_IDE_CHIPSETS is not set
# CONFIG_BLK_DEV_IDEDMA is not set
# CONFIG_IDEDMA_AUTO is not set
# CONFIG_BLK_DEV_HD is not set

#
# SCSI device support
#
# CONFIG_SCSI is not set

#
# Old CD-ROM drivers (not SCSI, not IDE)
#
# CONFIG_CD_NO_IDESCSI is not set

#
# Multi-device support (RAID and LVM)
#
# CONFIG_MD is not set

#
# Fusion MPT device support
#
# CONFIG_FUSION is not set

#
# IEEE 1394 (FireWire) support
#
# CONFIG_IEEE1394 is not set

#
# I2O device support
#
# CONFIG_I2O is not set

#
# Networking support
#
# CONFIG_NET is not set

#
# Amateur Radio support
#
# CONFIG_HAMRADIO is not set
# CONFIG_KGDBOE is not set
# CONFIG_NETPOLL is not set
# CONFIG_NETPOLL_RX is not set
# CONFIG_NETPOLL_TRAP is not set
# CONFIG_NET_POLL_CONTROLLER is not set

#
# ISDN subsystem
#

#
# Telephony Support
#
# CONFIG_PHONE is not set

#
# Input device support
#
CONFIG_INPUT=y

#
# Userland interfaces
#
# CONFIG_INPUT_MOUSEDEV is not set
# CONFIG_INPUT_JOYDEV is not set
# CONFIG_INPUT_TSDEV is not set
# CONFIG_INPUT_EVDEV is not set
# CONFIG_INPUT_EVBUG is not set

#
# Input I/O drivers
#
# CONFIG_GAMEPORT is not set
CONFIG_SOUND_GAMEPORT=y
CONFIG_SERIO=y
CONFIG_SERIO_I8042=y
# CONFIG_SERIO_SERPORT is not set
# CONFIG_SERIO_CT82C710 is not set
# CONFIG_SERIO_PCIPS2 is not set

#
# Input Device Drivers
#
CONFIG_INPUT_KEYBOARD=y
CONFIG_KEYBOARD_ATKBD=y
# CONFIG_KEYBOARD_SUNKBD is not set
# CONFIG_KEYBOARD_LKKBD is not set
# CONFIG_KEYBOARD_XTKBD is not set
# CONFIG_KEYBOARD_NEWTON is not set
# CONFIG_INPUT_MOUSE is not set
# CONFIG_INPUT_JOYSTICK is not set
# CONFIG_INPUT_TOUCHSCREEN is not set
# CONFIG_INPUT_MISC is not set

#
# Character devices
#
CONFIG_VT=y
CONFIG_VT_CONSOLE=y
CONFIG_HW_CONSOLE=y
# CONFIG_SERIAL_NONSTANDARD is not set

#
# Serial drivers
#
# CONFIG_SERIAL_8250 is not set

#
# Non-8250 serial port support
#
# CONFIG_UNIX98_PTYS is not set
# CONFIG_LEGACY_PTYS is not set
# CONFIG_QIC02_TAPE is not set

#
# IPMI
#
# CONFIG_IPMI_HANDLER is not set

#
# Watchdog Cards
#
# CONFIG_WATCHDOG is not set
# CONFIG_HW_RANDOM is not set
# CONFIG_NVRAM is not set
# CONFIG_RTC is not set
# CONFIG_GEN_RTC is not set
# CONFIG_DTLK is not set
# CONFIG_R3964 is not set
# CONFIG_APPLICOM is not set
# CONFIG_SONYPI is not set

#
# Ftape, the floppy tape device driver
#
# CONFIG_FTAPE is not set
# CONFIG_AGP is not set
# CONFIG_DRM is not set
# CONFIG_MWAVE is not set
# CONFIG_RAW_DRIVER is not set
# CONFIG_HANGCHECK_TIMER is not set

#
# I2C support
#
# CONFIG_I2C is not set

#
# Misc devices
#
# CONFIG_IBM_ASM is not set

#
# Multimedia devices
#
# CONFIG_VIDEO_DEV is not set

#
# Digital Video Broadcasting Devices
#

#
# Graphics support
#
CONFIG_FB=y
# CONFIG_FB_PM2 is not set
# CONFIG_FB_CYBER2000 is not set
# CONFIG_FB_IMSTT is not set
# CONFIG_FB_VGA16 is not set
CONFIG_FB_VESA=y
CONFIG_VIDEO_SELECT=y
# CONFIG_FB_HGA is not set
# CONFIG_FB_RIVA is not set
# CONFIG_FB_MATROX is not set
# CONFIG_FB_RADEON_OLD is not set
# CONFIG_FB_RADEON is not set
# CONFIG_FB_ATY128 is not set
# CONFIG_FB_ATY is not set
# CONFIG_FB_SIS is not set
# CONFIG_FB_NEOMAGIC is not set
# CONFIG_FB_KYRO is not set
# CONFIG_FB_3DFX is not set
# CONFIG_FB_VOODOO1 is not set
# CONFIG_FB_TRIDENT is not set
# CONFIG_FB_VIRTUAL is not set

#
# Console display driver support
#
CONFIG_VGA_CONSOLE=y
# CONFIG_MDA_CONSOLE is not set
CONFIG_DUMMY_CONSOLE=y
CONFIG_FRAMEBUFFER_CONSOLE=y
CONFIG_PCI_CONSOLE=y
# CONFIG_FONTS is not set
CONFIG_FONT_8x8=y
CONFIG_FONT_8x16=y

#
# Logo configuration
#
# CONFIG_LOGO is not set

#
# Sound
#
# CONFIG_SOUND is not set

#
# USB support
#
# CONFIG_USB is not set

#
# USB Gadget Support
#
# CONFIG_USB_GADGET is not set

#
# File systems
#
# CONFIG_EXT2_FS is not set
CONFIG_EXT3_FS=y
CONFIG_EXT3_FS_XATTR=y
CONFIG_EXT3_FS_POSIX_ACL=y
# CONFIG_EXT3_FS_SECURITY is not set
CONFIG_JBD=y
# CONFIG_JBD_DEBUG is not set
CONFIG_FS_MBCACHE=y
# CONFIG_REISERFS_FS is not set
# CONFIG_JFS_FS is not set
CONFIG_FS_POSIX_ACL=y
# CONFIG_XFS_FS is not set
# CONFIG_MINIX_FS is not set
# CONFIG_ROMFS_FS is not set
# CONFIG_QUOTA is not set
# CONFIG_AUTOFS_FS is not set
# CONFIG_AUTOFS4_FS is not set

#
# CD-ROM/DVD Filesystems
#
# CONFIG_ISO9660_FS is not set
# CONFIG_UDF_FS is not set

#
# DOS/FAT/NT Filesystems
#
# CONFIG_FAT_FS is not set
# CONFIG_NTFS_FS is not set

#
# Pseudo filesystems
#
CONFIG_PROC_FS=y
CONFIG_PROC_KCORE=y
# CONFIG_DEVFS_FS is not set
# CONFIG_TMPFS is not set
# CONFIG_HUGETLBFS is not set
# CONFIG_HUGETLB_PAGE is not set
CONFIG_RAMFS=y

#
# Miscellaneous filesystems
#
# CONFIG_ADFS_FS is not set
# CONFIG_AFFS_FS is not set
# CONFIG_HFS_FS is not set
# CONFIG_HFSPLUS_FS is not set
# CONFIG_BEFS_FS is not set
# CONFIG_BFS_FS is not set
# CONFIG_EFS_FS is not set
# CONFIG_CRAMFS is not set
# CONFIG_VXFS_FS is not set
# CONFIG_HPFS_FS is not set
# CONFIG_QNX4FS_FS is not set
# CONFIG_SYSV_FS is not set
# CONFIG_UFS_FS is not set

#
# Partition Types
#
# CONFIG_PARTITION_ADVANCED is not set
CONFIG_MSDOS_PARTITION=y

#
# Native Language Support
#
# CONFIG_NLS is not set

#
# Profiling support
#
# CONFIG_PROFILING is not set

#
# Kernel hacking
#
# CONFIG_DEBUG_KERNEL is not set
# CONFIG_EARLY_PRINTK is not set
# CONFIG_DEBUG_SPINLOCK_SLEEP is not set
# CONFIG_MMAP_TOPDOWN is not set
# CONFIG_FRAME_POINTER is not set
CONFIG_4KSTACKS=y
# CONFIG_SCHEDSTATS is not set

#
# Security options
#
# CONFIG_SECURITY is not set

#
# Cryptographic options
#
# CONFIG_CRYPTO is not set

#
# Library routines
#
# CONFIG_CRC32 is not set
CONFIG_X86_BIOS_REBOOT=y
</code>

Bartosz Tarnowski <haael@interia.pl>