Re: [PATCH 1/2] mm, memory_hotplug: do not fail offlining too early

From: Anshuman Khandual <khandual@linux.vnet.ibm.com>
To: Michael Ellerman <mpe@ellerman.id.au>, Michal Hocko <mhocko@kernel.org>
Cc: Andrew Morton <akpm@linux-foundation.org>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>,
	Reza Arbab <arbab@linux.vnet.ibm.com>,
	Yasuaki Ishimatsu <yasu.isimatu@gmail.com>,
	qiuxishi@huawei.com, Igor Mammedov <imammedo@redhat.com>,
	Vitaly Kuznetsov <vkuznets@redhat.com>,
	linux-mm@kvack.org, LKML <linux-kernel@vger.kernel.org>,
	Vlastimil Babka <vbabka@suse.cz>
Subject: Re: [PATCH 1/2] mm, memory_hotplug: do not fail offlining too early
Date: Wed, 11 Oct 2017 19:35:04 +0530	[thread overview]
Message-ID: <fa9bd463-bb94-f060-bd57-2a1416a125df@linux.vnet.ibm.com> (raw)
In-Reply-To: <87a80yz2gm.fsf@concordia.ellerman.id.au>

On 10/11/2017 10:49 AM, Michael Ellerman wrote:
> Michael Ellerman <mpe@ellerman.id.au> writes:
>> Michal Hocko <mhocko@kernel.org> writes:
>>> On Tue 10-10-17 23:05:08, Michael Ellerman wrote:
>>>> Michal Hocko <mhocko@kernel.org> writes:
>>>>> From: Michal Hocko <mhocko@suse.com>
>>>>> Memory offlining can fail just too eagerly under a heavy memory pressure.
>>>>>
>>>>> [ 5410.336792] page:ffffea22a646bd00 count:255 mapcount:252 mapping:ffff88ff926c9f38 index:0x3
>>>>> [ 5410.336809] flags: 0x9855fe40010048(uptodate|active|mappedtodisk)
>>>>> [ 5410.336811] page dumped because: isolation failed
>>>>> [ 5410.336813] page->mem_cgroup:ffff8801cd662000
>>>>> [ 5420.655030] memory offlining [mem 0x18b580000000-0x18b5ffffffff] failed
>>>>>
>>>>> Isolation has failed here because the page is not on LRU. Most probably
>>>>> because it was on the pcp LRU cache or it has been removed from the LRU
>>>>> already but it hasn't been freed yet. In both cases the page doesn't look
>>>>> non-migrable so retrying more makes sense.
>>>> This breaks offline for me.
>>>>
>>>> Prior to this commit:
>>>>   /sys/devices/system/memory/memory0# time echo 0 > online
>>>>   -bash: echo: write error: Device or resource busy
>>>>   
>>>>   real	0m0.001s
>>>>   user	0m0.000s
>>>>   sys	0m0.001s
>>>>
>>>> After:
>>>>   /sys/devices/system/memory/memory0# time echo 0 > online
>>>>   -bash: echo: write error: Device or resource busy
>>>>   
>>>>   real	2m0.009s
>>>>   user	0m0.000s
>>>>   sys	1m25.035s
>>>>
>>>> There's no way that block can be removed, it contains the kernel text,
>>>> so it should instantly fail - which it used to.
>>> OK, that means that start_isolate_page_range should have failed but it
>>> hasn't for some reason. I strongly suspect has_unmovable_pages is doing
>>> something wrong. Is the kernel text marked somehow? E.g. PageReserved?
>> I'm not sure how the text is marked, will have to dig into that.
> Yeah it's reserved:
> 
>   $ grep __init_begin /proc/kallsyms
>   c000000000d70000 T __init_begin
>   $ ./page-types -r -a 0x0,0xd7
>                flags	page-count       MB  symbolic-flags			long-symbolic-flags
>   0x0000000100000000	       215       13  __________________________r_______________	reserved
>                total	       215       13

Hey Michael,

What tool is this 'page-types' ?