Date:   Wed, 18 Aug 2021 09:24:01 +0200
From:   David Hildenbrand <david@...hat.com>
To:     Naoya Horiguchi <naoya.horiguchi@...ux.dev>,
        Yang Shi <shy828301@...il.com>
Cc:     osalvador@...e.de, tdmackey@...tter.com, akpm@...ux-foundation.org,
        corbet@....net, linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        Naoya Horiguchi <naoya.horiguchi@....com>
Subject: Re: [PATCH 1/2] mm: hwpoison: don't drop slab caches for offlining
 non-LRU page

On 18.08.21 08:30, Naoya Horiguchi wrote:
> On Mon, Aug 16, 2021 at 11:09:08AM -0700, Yang Shi wrote:
>> In the current implementation of soft offline, if non-LRU page is met,
>> all the slab caches will be dropped to free the page then offline.  But
>> if the page is not slab page all the effort is wasted in vain.  Even
>> though it is a slab page, it is not guaranteed the page could be freed
>> at all.
>>
>> However the side effect and cost is quite high.  It does not only drop
>> the slab caches, but also may drop a significant amount of page caches
>> which are associated with inode caches.  It could make the most
>> workingset gone in order to just offline a page.  And the offline is not
>> guaranteed to succeed at all, actually I really doubt the success rate
>> for real life workload.
>>
>> Furthermore the worse consequence is the system may be locked up and
>> unusable since the page cache release may incur huge amount of works
>> queued for memcg release.
>>
>> Actually we ran into such unpleasant case in our production environment.
>> Firstly, the workqueue of memory_failure_work_func is locked up as
>> below:
>>
>> BUG: workqueue lockup - pool cpus=1 node=0 flags=0x0 nice=0 stuck for 53s!
>> Showing busy workqueues and worker pools:
>> workqueue events: flags=0x0
>>    pwq 2: cpus=1 node=0 flags=0x0 nice=0 active=14/256 refcnt=15
>>      in-flight: 409271:memory_failure_work_func
>>      pending: kfree_rcu_work, kfree_rcu_monitor, kfree_rcu_work, rht_deferred_worker, rht_deferred_worker, rht_deferred_worker, rht_deferred_worker, kfree_rcu_work, kfree_rcu_work, kfree_rcu_work, kfree_rcu_work, drain_local_stock, kfree_rcu_work
>> workqueue mm_percpu_wq: flags=0x8
>>    pwq 2: cpus=1 node=0 flags=0x0 nice=0 active=1/256 refcnt=2
>>      pending: vmstat_update
>> workqueue cgroup_destroy: flags=0x0
>>    pwq 2: cpus=1 node=0 flags=0x0 nice=0 active=1/1 refcnt=12072
>>      pending: css_release_work_fn
>>
>> There were over 12K css_release_work_fn queued, and this caused a few
>> lockups due to the contention of worker pool lock with IRQ disabled, for
>> example:
>>
>> NMI watchdog: Watchdog detected hard LOCKUP on cpu 1
>> Modules linked in: amd64_edac_mod edac_mce_amd crct10dif_pclmul crc32_pclmul ghash_clmulni_intel xt_DSCP iptable_mangle kvm_amd bpfilter vfat fat acpi_ipmi i2c_piix4 usb_storage ipmi_si k10temp i2c_core ipmi_devintf ipmi_msghandler acpi_cpufreq sch_fq_codel xfs libcrc32c crc32c_intel mlx5_core mlxfw nvme xhci_pci ptp nvme_core pps_core xhci_hcd
>> CPU: 1 PID: 205500 Comm: kworker/1:0 Tainted: G             L    5.10.32-t1.el7.twitter.x86_64 #1
>> Hardware name: TYAN F5AMT /z        /S8026GM2NRE-CGN, BIOS V8.030 03/30/2021
>> Workqueue: events memory_failure_work_func
>> RIP: 0010:queued_spin_lock_slowpath+0x41/0x1a0
>> Code: 41 f0 0f ba 2f 08 0f 92 c0 0f b6 c0 c1 e0 08 89 c2 8b 07 30 e4 09 d0 a9 00 01 ff ff 75 1b 85 c0 74 0e 8b 07 84 c0 74 08 f3 90 <8b> 07 84 c0 75 f8 b8 01 00 00 00 66 89 07 c3 f6 c4 01 75 04 c6 47
>> RSP: 0018:ffff9b2ac278f900 EFLAGS: 00000002
>> RAX: 0000000000480101 RBX: ffff8ce98ce71800 RCX: 0000000000000084
>> RDX: 0000000000000000 RSI: 0000000000000000 RDI: ffff8ce98ce6a140
>> RBP: 00000000000284c8 R08: ffffd7248dcb6808 R09: 0000000000000000
>> R10: 0000000000000003 R11: ffff9b2ac278f9b0 R12: 0000000000000001
>> R13: ffff8cb44dab9c00 R14: ffffffffbd1ce6a0 R15: ffff8cacaa37f068
>> FS:  0000000000000000(0000) GS:ffff8ce98ce40000(0000) knlGS:0000000000000000
>> CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
>> CR2: 00007fcf6e8cb000 CR3: 0000000a0c60a000 CR4: 0000000000350ee0
>> Call Trace:
>>   __queue_work+0xd6/0x3c0
>>   queue_work_on+0x1c/0x30
>>   uncharge_batch+0x10e/0x110
>>   mem_cgroup_uncharge_list+0x6d/0x80
>>   release_pages+0x37f/0x3f0
>>   __pagevec_release+0x1c/0x50
>>   __invalidate_mapping_pages+0x348/0x380
>>   ? xfs_alloc_buftarg+0xa4/0x120 [xfs]
>>   inode_lru_isolate+0x10a/0x160
>>   ? iput+0x1d0/0x1d0
>>   __list_lru_walk_one+0x7b/0x170
>>   ? iput+0x1d0/0x1d0
>>   list_lru_walk_one+0x4a/0x60
>>   prune_icache_sb+0x37/0x50
>>   super_cache_scan+0x123/0x1a0
>>   do_shrink_slab+0x10c/0x2c0
>>   shrink_slab+0x1f1/0x290
>>   drop_slab_node+0x4d/0x70
>>   soft_offline_page+0x1ac/0x5b0
>>   ? dev_mce_log+0xee/0x110
>>   ? notifier_call_chain+0x39/0x90
>>   memory_failure_work_func+0x6a/0x90
>>   process_one_work+0x19e/0x340
>>   ? process_one_work+0x340/0x340
>>   worker_thread+0x30/0x360
>>   ? process_one_work+0x340/0x340
>>   kthread+0x116/0x130
>>
>> The lockup made the machine is quite unusable.  And it also made the
>> most workingset gone, the reclaimabled slab caches were reduced from 12G
>> to 300MB, the page caches were decreased from 17G to 4G.
>>
>> But the most disappointing thing is all the effort doesn't make the page
>> offline, it just returns:
>>
>> soft_offline: 0x1469f2: unknown non LRU page type 5ffff0000000000 ()
>>
>> It seems the aggressive behavior for non-LRU page didn't pay back, so it
>> doesn't make too much sense to keep it considering the terrible side
>> effect.
>>
>> Reported-by: David Mackey <tdmackey@...tter.com>
>> Cc: Naoya Horiguchi <naoya.horiguchi@....com>
>> Cc: Oscar Salvador <osalvador@...e.de>
>> Signed-off-by: Yang Shi <shy828301@...il.com>
> 
> Thank you. I agree with the idea of dropping drop_slab_node() in shake_page(),
> hoping that range-based slab shrinker will be implemented in the future.
> 
> This patch conflicts with the patch
> https://lore.kernel.org/linux-mm/20210817053703.2267588-1-naoya.horiguchi@linux.dev/T/#u
> which adds another shake_page(), so could you add the following hunk in your patch?
> 
> diff --git a/mm/memory-failure.c b/mm/memory-failure.c
> index 64f8ac969544..7dd2ca665866 100644
> --- a/mm/memory-failure.c
> +++ b/mm/memory-failure.c
> @@ -1198,7 +1198,7 @@ static int get_any_page(struct page *p, unsigned long flags)
>   			 * page, retry.
>   			 */
>   			if (pass++ < 3) {
> -				shake_page(p, 1);
> +				shake_page(p);
>   				goto try_again;
>   			}
>   			goto out;
> 
> 
> Thanks,
> Naoya Horiguchi
> 

Might we want to add a TODO in the code? We have a similar one in 
mm/page_isolation.c:set_migratetype_isolate() and it's certainly a 
reminder that something of value is missing.

-- 
Thanks,

David / dhildenb

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