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From:   Anshuman Khandual <anshuman.khandual@arm.com>
Subject: Re: [PATCH 0/5] mm, memory_hotplug: improve memory offlining failures
 debugging
To:     Michal Hocko <mhocko@kernel.org>,
        Andrew Morton <akpm@linux-foundation.org>
Cc:     Oscar Salvador <OSalvador@suse.com>, Baoquan He <bhe@redhat.com>,
        linux-mm@kvack.org, LKML <linux-kernel@vger.kernel.org>
References: <20181116083020.20260-1-mhocko@kernel.org>
Message-ID: <8a91e93d-386d-f0bc-d639-a696bb37a34e@arm.com>
Date:   Fri, 16 Nov 2018 17:25:35 +0530
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On 11/16/2018 02:00 PM, Michal Hocko wrote:
> Hi,
> this has been posted as an RFC [1]. I have screwed during rebasing so
> there were few compilation issues in the previous version. I have also
> integrated review feedback from Andrew and Anshuman.
> 
> I have been promissing to improve memory offlining failures debugging
> for quite some time. As things stand now we get only very limited
> information in the kernel log when the offlining fails. It is usually
> only
> [ 1984.506184] rac1 kernel: memory offlining [mem 0x82600000000-0x8267fffffff] failed
> without no further details. We do not know what exactly fails and for
> what reason. Whenever I was forced to debug such a failure I've always
> had to do a debugging patch to tell me more. We can enable some
> tracepoints but it would be much better to get a better picture without
> using them.
> 
> This patch series does 2 things. The first one is to make dump_page
> more usable by printing more information about the mapping patch 1.
> Then it reduces the log level from emerg to warning so that this
> function is usable from less critical context patch 2. Then I have
> added more detailed information about the offlining failure patch 4
> and finally add dump_page to isolation and offlining migration paths.
> Patch 3 is a trivial cleanup.
> 
> Does this look go to you?
> 
> [1] http://lkml.kernel.org/r/20181107101830.17405-1-mhocko@kernel.org
> 

Agreed. It has been always difficult to debug memory hot plug problems
without a debug patch particularly to understand the unmovable pages
and their isolation failures in the range to be removed. This series
is definitely going to help improve the situation.