Date:   Fri, 20 Aug 2021 09:08:39 +0200
From:   David Hildenbrand <david@...hat.com>
To:     Yang Shi <shy828301@...il.com>, naoya.horiguchi@....com,
        osalvador@...e.de, tdmackey@...tter.com, willy@...radead.org,
        akpm@...ux-foundation.org, corbet@....net
Cc:     linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [v2 PATCH 1/3] mm: hwpoison: don't drop slab caches for offlining
 non-LRU page

On 19.08.21 07:41, 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>
> Cc: David Hildenbrand <david@...hat.com>
> Signed-off-by: Yang Shi <shy828301@...il.com>
> ---
Acked-by: David Hildenbrand <david@...hat.com>

-- 
Thanks,

David / dhildenb

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