linux-kernel - Re: [PATCH] x86_64: uninline TASK

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Date:   Mon, 22 Apr 2019 00:10:07 +0300
From:   Alexey Dobriyan <adobriyan@...il.com>
To:     hpa@...or.com
Cc:     Ingo Molnar <mingo@...nel.org>, tglx@...utronix.de,
        mingo@...hat.com, bp@...en8.de, linux-kernel@...r.kernel.org,
        x86@...nel.org
Subject: Re: [PATCH] x86_64: uninline TASK_SIZE

On Sun, Apr 21, 2019 at 01:07:08PM -0700, hpa@...or.com wrote:
> On April 21, 2019 11:28:42 AM PDT, Ingo Molnar <mingo@...nel.org> wrote:
> >
> >* Alexey Dobriyan <adobriyan@...il.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@...il.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?

Maybe. I only thought about putting every 32-bit related flag under
CONFIG_COMPAT to further eradicate bloat (and force everyone else
to keep an eye on it, ha-ha).