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

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Message-ID: <20181116112603.GI14706@dhcp22.suse.cz>
Date:   Fri, 16 Nov 2018 12:26:03 +0100
From:   Michal Hocko <mhocko@...nel.org>
To:     osalvador <osalvador@...e.de>
Cc:     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 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
-- 
Michal Hocko
SUSE Labs