Re: [PATCH] mm: use managed_zone() for more exact check in zone iteration

[Wei Yang]

On Fri, Nov 16, 2018 at 12:26:03PM +0100, Michal Hocko wrote:
>On Fri 16-11-18 12:05:04, osalvador wrote:
>> On Fri, 2018-11-16 at 10:57 +0100, Michal Hocko wrote:
>[...]
>> > E.g. memory hotplug decreases both managed and present counters. I
>> > am actually not sure that is 100% correct (put on my TODO list to
>> > check). There is no consistency in that regards.
>> 
>> We can only offline non-reserved pages (so, managed pages).
>
>Yes
>
>> Since present pages holds reserved_pages + managed_pages, decreasing
>> both should be fine unless I am mistaken.
>
>Well, present_pages is defined as "physical pages existing within the zone"
>and those pages are still existing but they are offline. But as I've
>said I have to think about it some more

I may not catch up with your discussions, while I'd like to share what I
learnt.

online_pages()
    online_pages_range()
    zone->present_pages += onlined_pages;

__offline_pages()
    adjust_managed_page_count()
    zone->present_pages -= offlined_pages;

The two counters: present_pages & managed_pages would be adjusted during
online/offline.

While I am not sure when *reserved_pages* would be adjusted. Will we add
this hot-added memory into memblock.reserved? and allocate memory by
memblock_alloc() after system bootup?

>-- 
>Michal Hocko
>SUSE Labs

-- 
Wei Yang
Help you, Help me