[PATCH] x86_64: uninline TASK_SIZE

[Alexey Dobriyan]

TASK_SIZE macro is quite deceptive: it looks like a constant but in fact
compiles to 50+ bytes.

Space savings on x86_64 defconfig:

add/remove: 1/0 grow/shrink: 3/24 up/down: 77/-2247 (-2170)
Function                                     old     new   delta
_task_size                                     -      52     +52
mpol_shared_policy_init                      344     363     +19
shmem_get_unmapped_area                       92      97      +5
__rseq_handle_notify_resume.cold              34      35      +1
copy_from_user_nmi                           123     113     -10
mmap_address_hint_valid                       92      56     -36
arch_get_unmapped_area_topdown               471     435     -36
tlb_gather_mmu                               164     126     -38
hugetlb_get_unmapped_area                    774     736     -38
__create_xol_area                            497     458     -39
arch_tlb_gather_mmu                          160     120     -40
setup_new_exec                               380     336     -44
__x64_sys_mlockall                           378     333     -45
__ia32_sys_mlockall                          378     333     -45
tlb_flush_mmu                                235     189     -46
unmap_page_range                            2098    2048     -50
copy_mount_options                           518     465     -53
__get_user_pages                            1737    1675     -62
get_unmapped_area                            270     204     -66
perf_prepare_sample                         1176    1098     -78
perf_callchain_user                          549     469     -80
mremap_to.isra                               545     457     -88
arch_tlb_finish_mmu                          394     305     -89
__do_munmap                                 1039     927    -112
elf_map                                      527     409    -118
prctl_set_mm                                1509    1335    -174
__rseq_handle_notify_resume                 1116     906    -210
load_elf_binary                            11761   11111    -650
Total: Before=14121337, After=14119167, chg -0.02%

Signed-off-by: Alexey Dobriyan <adobriyan@xxxxxxxxx>
---

 arch/x86/include/asm/processor.h |    4 ++--
 arch/x86/kernel/Makefile         |    1 +
 arch/x86/kernel/task_size_64.c   |    9 +++++++++
 3 files changed, 12 insertions(+), 2 deletions(-)

--- a/arch/x86/include/asm/processor.h
+++ b/arch/x86/include/asm/processor.h
@@ -887,8 +887,8 @@ static inline void spin_lock_prefetch(const void *x)
 
 #define TASK_SIZE_LOW		(test_thread_flag(TIF_ADDR32) ? \
 					IA32_PAGE_OFFSET : DEFAULT_MAP_WINDOW)
-#define TASK_SIZE		(test_thread_flag(TIF_ADDR32) ? \
-					IA32_PAGE_OFFSET : TASK_SIZE_MAX)
+unsigned long _task_size(void);
+#define TASK_SIZE		_task_size()
 #define TASK_SIZE_OF(child)	((test_tsk_thread_flag(child, TIF_ADDR32)) ? \
 					IA32_PAGE_OFFSET : TASK_SIZE_MAX)
 
--- a/arch/x86/kernel/Makefile
+++ b/arch/x86/kernel/Makefile
@@ -46,6 +46,7 @@ CFLAGS_irq.o := -I$(src)/../include/asm/trace
 
 obj-y			:= process_$(BITS).o signal.o
 obj-$(CONFIG_COMPAT)	+= signal_compat.o
+obj-$(CONFIG_X86_64)	+= task_size_64.o
 obj-y			+= traps.o idt.o irq.o irq_$(BITS).o dumpstack_$(BITS).o
 obj-y			+= time.o ioport.o dumpstack.o nmi.o
 obj-$(CONFIG_MODIFY_LDT_SYSCALL)	+= ldt.o
new file mode 100644
--- /dev/null
+++ b/arch/x86/kernel/task_size_64.c
@@ -0,0 +1,9 @@
+#include <linux/export.h>
+#include <linux/sched.h>
+#include <linux/thread_info.h>
+
+unsigned long _task_size(void)
+{
+	return test_thread_flag(TIF_ADDR32) ? IA32_PAGE_OFFSET : TASK_SIZE_MAX;
+}
+EXPORT_SYMBOL(_task_size);