Re: [PATCH] mm/page_alloc: call set_pageblock_order() once for each node

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

On Thu, Apr 05, 2018 at 11:55:50AM +0200, Michal Hocko wrote:
>On Wed 04-04-18 09:27:34, Wei Yang wrote:
>> On Tue, Apr 03, 2018 at 09:57:37AM +0200, Michal Hocko wrote:
>> >On Fri 30-03-18 09:02:43, Wei Yang wrote:
>> >> On Thu, Mar 29, 2018 at 01:11:09PM +0100, Mel Gorman wrote:
>> >> >On Thu, Mar 29, 2018 at 11:36:07AM +0800, Wei Yang wrote:
>> >> >> set_pageblock_order() is a standalone function which sets pageblock_order,
>> >> >> while current implementation calls this function on each ZONE of each node
>> >> >> in free_area_init_core().
>> >> >> 
>> >> >> Since free_area_init_node() is the only user of free_area_init_core(),
>> >> >> this patch moves set_pageblock_order() up one level to invoke
>> >> >> set_pageblock_order() only once on each node.
>> >> >> 
>> >> >> Signed-off-by: Wei Yang <richard.weiyang@gmail.com>
>> >> >
>> >> >The patch looks ok but given that set_pageblock_order returns immediately
>> >> >if it has already been called, I expect the benefit is marginal. Was any
>> >> >improvement in boot time measured?
>> >> 
>> >> No, I don't expect measurable improvement from this since the number of nodes
>> >> and zones are limited.
>> >> 
>> >> This is just a code refine from logic point of view.
>> >
>> >Then, please make sure it is a real refinement. Calling this function
>> >per node is only half way to get there as the function is by no means
>> >per node.
>> >
>> 
>> Hi, Michal
>> 
>> I guess you are willing to see this function is only called once for the whole
>> system.
>> 
>> Yes, that is the ideal way, well I don't come up with an elegant way. The best
>> way is to move this to free_area_init_nodes(), while you can see not all arch
>> use this function.
>> 
>> Then I have two options:
>> 
>> A: Move this to free_area_init_nodes() for those arch using it. Call it
>> specifically for those arch not using free_area_init_nodes().
>> 
>> B: call it before setup_arch() in start_kernel()
>> 
>> Hmm... which one you would prefer? If you have a better idea, that would be
>> great.
>
>or
>C: do nothing and/or just document why do we call it this way
>(convenience).

Ok, maybe we can leave it alone now.

>-- 
>Michal Hocko
>SUSE Labs

-- 
Wei Yang
Help you, Help me