Re: [PATCH] x86_64: uninline TASK_SIZE

Ingo Molnar
2019-04-21T18:28:50Z

* Alexey Dobriyan <adobriyan@gmail.com> wrote:

> 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);

Good idea - but instead of adding yet another compilation unit, why not
stick _task_size() into arch/x86/kernel/process_64.c, which is the
canonical place for process management related arch functions?

Thanks,

Ingo