linux-kernel - Re: [PATCH 1/2] mm: drop migrate type checks from has_unmovable

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Message-ID: <20171017120318.rers7zga3cnirt4i@dhcp22.suse.cz>
Date:   Tue, 17 Oct 2017 14:03:18 +0200
From:   Michal Hocko <mhocko@...nel.org>
To:     Michael Ellerman <mpe@...erman.id.au>,
        Andrew Morton <akpm@...ux-foundation.org>
Cc:     linux-mm@...ck.org, Vlastimil Babka <vbabka@...e.cz>,
        KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
        Reza Arbab <arbab@...ux.vnet.ibm.com>,
        Yasuaki Ishimatsu <yasu.isimatu@...il.com>,
        qiuxishi@...wei.com, Igor Mammedov <imammedo@...hat.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/2] mm: drop migrate type checks from has_unmovable_pages

On Tue 17-10-17 22:41:08, Michael Ellerman wrote:
> Michal Hocko <mhocko@...nel.org> writes:
> 
> > From: Michal Hocko <mhocko@...e.com>
> >
> > Michael has noticed that the memory offline tries to migrate kernel code
> > pages when doing
> >  echo 0 > /sys/devices/system/memory/memory0/online
> >
> > The current implementation will fail the operation after several failed
> > page migration attempts but we shouldn't even attempt to migrate
> > that memory and fail right away because this memory is clearly not
> > migrateable. This will become a real problem when we drop the retry loop
> > counter resp. timeout.
> >
> > The real problem is in has_unmovable_pages in fact. We should fail if
> > there are any non migrateable pages in the area. In orther to guarantee
> > that remove the migrate type checks because MIGRATE_MOVABLE is not
> > guaranteed to contain only migrateable pages. It is merely a heuristic.
> > Similarly MIGRATE_CMA does guarantee that the page allocator doesn't
> > allocate any non-migrateable pages from the block but CMA allocations
> > themselves are unlikely to migrateable. Therefore remove both checks.
> >
> > Reported-by: Michael Ellerman <mpe@...erman.id.au>
> > Signed-off-by: Michal Hocko <mhocko@...e.com>
> 
> Thanks, that works for me.
> 
> Tested-by: Michael Ellerman <mpe@...erman.id.au>

Thanks a lot Michael!

Andrew, could you add these two patches and merge them before
mm-memory_hotplug-do-not-fail-offlining-too-early.patch? Or should I
rather repost the full series (including 2 already merged patches?
again?
-- 
Michal Hocko
SUSE Labs