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

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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






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