Re: [PATCH] mm, show_mem: drop pgdat_resize_lock in show_mem()

[Wei Yang <richard.weiyang@gmail.com>]

On Thu, Nov 29, 2018 at 04:49:22PM +0100, Michal Hocko wrote:
>On Thu 29-11-18 15:04:49, Wei Yang wrote:
>> On Thu, Nov 29, 2018 at 09:17:03AM +0100, Michal Hocko wrote:
>> >On Thu 29-11-18 05:08:15, Wei Yang wrote:
>> >> Function show_mem() is used to print system memory status when user
>> >> requires or fail to allocate memory. Generally, this is a best effort
>> >> information and not willing to affect core mm subsystem.
>> >
>> >I would drop the part after and
>> >
>> >> The data protected by pgdat_resize_lock is mostly correct except there is:
>> >> 
>> >>    * page struct defer init
>> >>    * memory hotplug
>> >
>> >This is more confusing than helpful. I would just drop it.
>> >
>> >The changelog doesn't explain what is done and why. The second one is
>> >much more important. I would say this
>> >
>> >"
>> >Function show_mem() is used to print system memory status when user
>> >requires or fail to allocate memory. Generally, this is a best effort
>> >information so any races with memory hotplug (or very theoretically an
>> >early initialization) should be toleratable and the worst that could
>> >happen is to print an imprecise node state.
>> >
>> >Drop the resize lock because this is the only place which might hold the
>> 
>> As I mentioned in https://patchwork.kernel.org/patch/10689759/, there is
>> one place used in __remove_zone(). I don't get your suggestion of this
>> place. And is __remove_zone() could be called in IRQ context?
>
>It is only called from __remove_pages and that one calls cond_resched so
>obviosly not.
>

Forgive my poor background knowledge, I went throught the code, but not
found where call cond_resched.

  __remove_pages()
    release_mem_region_adjustable()
    clear_zone_contiguous()
    __remove_section()
      unregister_memory_section()
      __remove_zone()
      sparse_remove_one_section()
    set_zone_contiguous()

Would you mind giving me a hint?

>-- 
>Michal Hocko
>SUSE Labs

-- 
Wei Yang
Help you, Help me