mm: Support compiling out madvise and fadvise

Many embedded systems will not need these syscalls, and omitting them
saves space.  Add a new EXPERT config option CONFIG_ADVISE_SYSCALLS
(default y) to support compiling them out.

bloat-o-meter:
add/remove: 0/3 grow/shrink: 0/0 up/down: 0/-2250 (-2250)
function                                     old     new   delta
sys_fadvise64                                 57       -     -57
sys_fadvise64_64                             691       -    -691
sys_madvise                                 1502       -   -1502

Signed-off-by: Josh Triplett <josh@joshtriplett.org>

init/Kconfig

@@ -1537,6 +1537,16 @@ config AIO
 	  by some high performance threaded applications. Disabling
 	  this option saves about 7k.
 
+config ADVISE_SYSCALLS
+	bool "Enable madvise/fadvise syscalls" if EXPERT
+	default y
+	help
+	  This option enables the madvise and fadvise syscalls, used by
+	  applications to advise the kernel about their future memory or file
+	  usage, improving performance. If building an embedded system where no
+	  applications use these syscalls, you can disable this option to save
+	  space.
+
 config PCI_QUIRKS
 	default y
 	bool "Enable PCI quirk workarounds" if EXPERT

kernel/sys_ni.c

@@ -156,6 +156,9 @@ cond_syscall(sys_process_vm_writev);
 cond_syscall(compat_sys_process_vm_readv);
 cond_syscall(compat_sys_process_vm_writev);
 cond_syscall(sys_uselib);
+cond_syscall(sys_fadvise64);
+cond_syscall(sys_fadvise64_64);
+cond_syscall(sys_madvise);
 
 /* arch-specific weak syscall entries */
 cond_syscall(sys_pciconfig_read);

mm/Makefile

@@ -3,7 +3,7 @@
 #
 
 mmu-y			:= nommu.o
-mmu-$(CONFIG_MMU)	:= fremap.o gup.o highmem.o madvise.o memory.o mincore.o \
+mmu-$(CONFIG_MMU)	:= fremap.o gup.o highmem.o memory.o mincore.o \
 			   mlock.o mmap.o mprotect.o mremap.o msync.o rmap.o \
 			   vmalloc.o pagewalk.o pgtable-generic.o
 
@@ -11,7 +11,7 @@ ifdef CONFIG_CROSS_MEMORY_ATTACH
 mmu-$(CONFIG_MMU)	+= process_vm_access.o
 endif
 
-obj-y			:= filemap.o mempool.o oom_kill.o fadvise.o \
+obj-y			:= filemap.o mempool.o oom_kill.o \
 			   maccess.o page_alloc.o page-writeback.o \
 			   readahead.o swap.o truncate.o vmscan.o shmem.o \
 			   util.o mmzone.o vmstat.o backing-dev.o \
@@ -28,6 +28,9 @@ else
 	obj-y		+= bootmem.o
 endif
 
+ifdef CONFIG_MMU
+	obj-$(CONFIG_ADVISE_SYSCALLS)	+= fadvise.o madvise.o
+endif
 obj-$(CONFIG_HAVE_MEMBLOCK) += memblock.o
 
 obj-$(CONFIG_SWAP)	+= page_io.o swap_state.o swapfile.o