Re: [PATCH 1/2] mm: hwpoison: don't drop slab caches for offlining non-LRU page

[David Hildenbrand]

On 16.08.21 21:02, David Hildenbrand wrote:
> On 16.08.21 20:09, 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
>
> Just curious, who actually ends up calling soft_offline_page() ? I
> cannot really make sense of this, looking at upstream Linux.
>
> I can spot
>
> a) drivers/base/memory.c: /sys/devices/system/memory/soft_offline_page
> seems to be a testing interface
>
> b) MADV_SOFT_OFFLINE seems to be a testing interface as well
>
> c) arch/parisc/kernel/pdt.c doesn't apply to your case I guess?
>
> I'm just wondering who ends up calling soft_offline_page() in a
> production environment and via which call path. I'm most probably
> missing something.

... and I missed memory_failure_work_func() with MF_SOFT_OFFLINE :)

Ignore my question :)

--
Thanks,

David / dhildenb