[PATCH] x86_64: uninline TASK_SIZE

Alexey Dobriyan
2019-04-21T16:06:07Z

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@gmail.com>
---

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);