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

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Message-ID: <20181116155828.strdglxqgqe4jqkr@master>
Date:   Fri, 16 Nov 2018 15:58:28 +0000
From:   Wei Yang <richard.weiyang@...il.com>
To:     Michal Hocko <mhocko@...nel.org>
Cc:     osalvador <osalvador@...e.de>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Wei Yang <richard.weiyang@...il.com>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mm: use managed_zone() for more exact check in zone
 iteration

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