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>

3 files changed, 18 insertions, 2 deletions

diff --git a/init/Kconfig b/init/Kconfig
index e84c6423a2e5..782a65bf76ea 100644
--- a/init/Kconfig
+++ b/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
diff --git a/kernel/sys_ni.c b/kernel/sys_ni.c
index 391d4ddb6f4b..d4709d481053 100644
--- a/kernel/sys_ni.c
+++ b/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);
diff --git a/mm/Makefile b/mm/Makefile
index 632ae77e6070..fe7a053c0f45 100644
--- a/mm/Makefile
+++ b/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