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From: Michael Ellerman <mpe@ellerman.id.au>
To: 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 13:37:50 +1100
Message-ID: <87infmz9xd.fsf@concordia.ellerman.id.au> (raw)
In-Reply-To: <20171010122726.6jrfdzkscwge6gez@dhcp22.suse.cz>

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.

> In other words, does the diff below helps?

No that doesn't help.

> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index 3badcedf96a7..00d042052501 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -7368,6 +7368,9 @@ bool has_unmovable_pages(struct zone *zone, struct page *page, int count,
>  
>  		page = pfn_to_page(check);
>  
> +		if (PageReserved(page))
> +			return true;
> +
>  		/*
>  		 * Hugepages are not in LRU lists, but they're movable.
>  		 * We need not scan over tail pages bacause we don't
>
>
>> With commit 3aa2823fdf66 ("mm, memory_hotplug: remove timeout from
>> __offline_memory") also applied, it appears to just get stuck forever,
>> and I get lots of:
>> 
>>   [ 1232.112953] INFO: task kworker/3:0:4609 blocked for more than 120 seconds.
>>   [ 1232.113067]       Not tainted 4.14.0-rc4-gcc6-next-20171009-g49827b9 #1
>>   [ 1232.113183] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
>>   [ 1232.113319] kworker/3:0     D11984  4609      2 0x00000800
>>   [ 1232.113416] Workqueue: memcg_kmem_cache memcg_kmem_cache_create_func
>>   [ 1232.113531] Call Trace:
>>   [ 1232.113579] [c0000000fb2db7a0] [c0000000fb2db900] 0xc0000000fb2db900 (unreliable)
>>   [ 1232.113717] [c0000000fb2db970] [c00000000001c964] __switch_to+0x304/0x6e0
>>   [ 1232.113840] [c0000000fb2dba10] [c000000000a408c0] __schedule+0x2e0/0xa80
>>   [ 1232.113978] [c0000000fb2dbae0] [c000000000a410a8] schedule+0x48/0xc0
>>   [ 1232.114113] [c0000000fb2dbb10] [c000000000a44d88] rwsem_down_read_failed+0x128/0x1b0
>>   [ 1232.114269] [c0000000fb2dbb70] [c0000000001696a8] __percpu_down_read+0x108/0x110
>>   [ 1232.114426] [c0000000fb2dbba0] [c00000000032e498] get_online_mems+0x68/0x80
>>   [ 1232.115487] [c0000000fb2dbbc0] [c0000000002c82ec] memcg_create_kmem_cache+0x4c/0x190
>>   [ 1232.115651] [c0000000fb2dbc60] [c0000000003483b8] memcg_kmem_cache_create_func+0x38/0xf0
>>   [ 1232.115809] [c0000000fb2dbc90] [c000000000121594] process_one_work+0x2b4/0x590
>>   [ 1232.115964] [c0000000fb2dbd20] [c000000000121908] worker_thread+0x98/0x5d0
>>   [ 1232.116095] [c0000000fb2dbdc0] [c00000000012a134] kthread+0x164/0x1b0
>>   [ 1232.116229] [c0000000fb2dbe30] [c00000000000bae0] ret_from_kernel_thread+0x5c/0x7c
>
> I do not see how this is related to the offline path.

It's blocked doing get_online_mems(). So it's unrelated to the offline,
but it can't proceed until the offline finishes, which it never does,
IIUIC.

cheers

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  reply index

Thread overview: 56+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2017-09-18  7:08 [PATCH v2 0/2] mm, memory_hotplug: redefine memory offline retry logic Michal Hocko
2017-09-18  7:08 ` [PATCH 1/2] mm, memory_hotplug: do not fail offlining too early Michal Hocko
2017-10-10 12:05   ` Michael Ellerman
2017-10-10 12:27     ` Michal Hocko
2017-10-11  2:37       ` Michael Ellerman [this message]
2017-10-11  5:19         ` Michael Ellerman
2017-10-11 14:05           ` Anshuman Khandual
2017-10-11 14:16             ` Michal Hocko
2017-10-11  6:51         ` Michal Hocko
2017-10-11  8:04           ` Vlastimil Babka
2017-10-11  8:13             ` Michal Hocko
2017-10-11 11:17               ` Vlastimil Babka
2017-10-11 11:24                 ` Michal Hocko
2017-10-13 11:42             ` Michael Ellerman
2017-10-13 11:58               ` Michal Hocko
2017-10-13 12:00                 ` [PATCH 1/2] mm: drop migrate type checks from has_unmovable_pages Michal Hocko
2017-10-13 12:00                   ` [PATCH 2/2] mm, page_alloc: fail has_unmovable_pages when seeing reserved pages Michal Hocko
2017-10-13 12:04                     ` Vlastimil Babka
2017-10-13 12:07                       ` Michal Hocko
2017-10-17 13:03                         ` Vlastimil Babka
2017-10-17 11:41                   ` [PATCH 1/2] mm: drop migrate type checks from has_unmovable_pages Michael Ellerman
2017-10-17 12:03                     ` Michal Hocko
2017-10-17 13:02                   ` Vlastimil Babka
2017-10-19  2:51                   ` Joonsoo Kim
2017-10-19  7:15                     ` Michal Hocko
2017-10-19  7:33                       ` Joonsoo Kim
2017-10-19  8:20                         ` Michal Hocko
2017-10-19 12:21                           ` Michal Hocko
2017-10-20  2:13                             ` Joonsoo Kim
2017-10-20  5:59                               ` Michal Hocko
2017-10-20  6:50                                 ` Joonsoo Kim
2017-10-20  7:02                                   ` Michal Hocko
2017-10-23  5:23                                     ` Joonsoo Kim
2017-10-23  8:10                                       ` Michal Hocko
2017-10-24  4:44                                         ` Joonsoo Kim
2017-10-24  7:44                                           ` Michal Hocko
2017-10-24  8:12                                           ` Vlastimil Babka
2017-10-24 12:25                                             ` Michal Hocko
2017-10-26  2:47                                             ` Joonsoo Kim
2017-10-26  7:41                                               ` Michal Hocko
2017-10-20  7:22                               ` Xishi Qiu
2017-10-20  8:17                                 ` Michal Hocko
2017-10-23  5:26                                   ` Joonsoo Kim
2017-10-26 13:04                             ` Vlastimil Babka
2017-10-26 13:59                             ` Michal Hocko
2017-09-18  7:08 ` [PATCH 2/2] mm, memory_hotplug: remove timeout from __offline_memory Michal Hocko
  -- strict thread matches above, loose matches on Subject: below --
2017-09-04  8:21 [PATCH 0/2] mm, memory_hotplug: redefine memory offline retry logic Michal Hocko
2017-09-04  8:21 ` [PATCH 1/2] mm, memory_hotplug: do not fail offlining too early Michal Hocko
2017-09-05  6:29   ` Anshuman Khandual
2017-09-05  7:13     ` Michal Hocko
2017-09-08 17:26   ` Vlastimil Babka
2017-09-11  8:17     ` Michal Hocko
2017-09-13 11:41       ` Vlastimil Babka
2017-09-13 12:10         ` Michal Hocko
2017-09-13 12:14           ` Michal Hocko
2017-09-13 12:19             ` Vlastimil Babka
2017-09-13 12:32               ` Michal Hocko

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