Re: [PATCH] x86_64: uninline TASK_SIZE

hpa
2019-04-21T20:07:36Z

On April 21, 2019 11:28:42 AM PDT, Ingo Molnar <mingo@kernel.org> wrote:
>
>* 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

Better yet... since TIF_ADDR32 isn't something that changes randomly, perhaps this should be a separate variable?
--
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