linux-kernel - Re: [PATCH] mm, memory_hotplug: check zone_movable in has_unmovable

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Message-ID: <20181107081426.GW27423@dhcp22.suse.cz>
Date:   Wed, 7 Nov 2018 09:14:26 +0100
From:   Michal Hocko <mhocko@...nel.org>
To:     osalvador <osalvador@...e.de>
Cc:     Balbir Singh <bsingharora@...il.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Baoquan He <bhe@...hat.com>, linux-mm@...ck.org,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] mm, memory_hotplug: check zone_movable in
 has_unmovable_pages

On Wed 07-11-18 08:55:26, osalvador wrote:
> On Wed, 2018-11-07 at 08:35 +0100, Michal Hocko wrote:
> > On Wed 07-11-18 07:35:18, Balbir Singh wrote:
> > > The check seems to be quite aggressive and in a loop that iterates
> > > pages, but has nothing to do with the page, did you mean to make
> > > the check
> > > 
> > > zone_idx(page_zone(page)) == ZONE_MOVABLE
> > 
> > Does it make any difference? Can we actually encounter a page from a
> > different zone here?
> 
> AFAIK, test_pages_in_a_zone() called from offline_pages() should ensure
> that the range belongs to a unique zone, so we should not encounter
> pages from other zones there, right?

Yes that is the case for memory hotplug. We do assume a single zone at
set_migratetype_isolate where we take the zone->lock. If the
contig_alloc can span multiple zones then it should check for similar.
-- 
Michal Hocko
SUSE Labs