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

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Message-ID: <1542366304.3020.15.camel@suse.de>
Date:   Fri, 16 Nov 2018 12:05:04 +0100
From:   osalvador <osalvador@...e.de>
To:     Michal Hocko <mhocko@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>
Cc:     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, 2018-11-16 at 10:57 +0100, Michal Hocko wrote:
> On Thu 15-11-18 13:37:35, Andrew Morton wrote:
> [...]
> > Worse, the situations in which managed_zone() != populated_zone()
> > are
> > rare(?), so it will take a long time for problems to be discovered,
> > I
> > expect.
> 
> We would basically have to deplete the whole zone by the bootmem
> allocator or pull out all pages from the page allocator. 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).
Since present pages holds reserved_pages + managed_pages, decreasing
both should be fine unless I am mistaken.

Oscar Salvador