Re: 4.3-rc1 dirty page count underflow (cgroup-related?)

[Greg Thelen]

Greg Thelen wrote:

> Dave Hansen wrote:
>
>> I've been seeing some strange behavior with 4.3-rc1 kernels on my Ubuntu
>> 14.04.3 system.  The system will run fine for a few hours, but suddenly
>> start becoming horribly I/O bound.  A compile of perf for instance takes
>> 20-30 minutes and the compile seems entirely I/O bound.  But, the SSD is
>> only seeing tens or hundreds of KB/s of writes.
>>
>> Looking at some writeback tracepoints shows it hitting
>> balance_dirty_pages() pretty hard with a pretty large number of dirty
>> pages. :)
>>
>>>               ld-27008 [000] ...1 88895.190770: balance_dirty_pages: bdi
>>> 8:0: limit=234545 setpoint=204851 dirty=18446744073709513951
>>> bdi_setpoint=184364 bdi_dirty=33 dirty_ratelimit=24 task_ratelimit=0
>>> dirtied=1 dirtied_pause=0 paused=0 pause=136 period=136 think=0
>>> cgroup=/user/1000.user/c2.session
>>
>> So something is underflowing dirty.
>>
>> I added the attached patch and got a warning pretty quickly, so this
>> looks pretty reproducible for me.
>>
>> I'm not 100% sure this is from the 4.3 merge window.  I was running the
>> 4.2-rcs, but they seemed to have their own issues.  Ubuntu seems to be
>> automatically creating some cgroups, so they're definitely in play here.
>>
>> Any ideas what is going on?
>>
>>> [   12.415472] ------------[ cut here ]------------
>>> [   12.415481] WARNING: CPU: 1 PID: 1684 at mm/page-writeback.c:2435 account_page_cleaned+0x101/0x110()
>>> [   12.415483] MEM_CGROUP_STAT_DIRTY bogus
>>> [   12.415484] Modules linked in: ipt_MASQUERADE nf_nat_masquerade_ipv4 iptable_nat nf_nat_ipv4 nf_nat nf_conntrack_ipv4 nf_defrag_ipv4 xt_conntrack nf_conntrack ipt_REJECT nf_reject_ipv4 xt_CHECKSUM iptable_mangle xt_tcpudp bridge stp llc iptable_filter ip_tables ebtable_nat ebtables x_tables dm_crypt cmac rfcomm bnep arc4 iwldvm mac80211 btusb snd_hda_codec_hdmi iwlwifi btrtl btbcm btintel snd_hda_codec_realtek snd_hda_codec_generic bluetooth snd_hda_intel snd_hda_codec cfg80211 snd_hwdep snd_hda_core intel_rapl iosf_mbi hid_logitech_hidpp x86_pkg_temp_thermal snd_pcm coretemp ghash_clmulni_intel thinkpad_acpi joydev snd_seq_midi snd_seq_midi_event snd_rawmidi nvram snd_seq snd_timer snd_seq_device wmi snd soundcore mac_hid lpc_ich aesni_intel aes_x86_64 glue_helper lrw gf128mul ablk_helper cryptd kvm_intel kvm hid_logitech_dj sdhci_pci sdhci usbhid hid
>>> [   12.415538] CPU: 1 PID: 1684 Comm: indicator-keybo Not tainted 4.3.0-rc1-dirty #25
>>> [   12.415540] Hardware name: LENOVO 2325AR2/2325AR2, BIOS G2ETA4WW (2.64 ) 04/09/2015
>>> [   12.415542]  ffffffff81aa8172 ffff8800c926ba30 ffffffff8132e3e2 ffff8800c926ba78
>>> [   12.415544]  ffff8800c926ba68 ffffffff8105e386 ffffea000fca4700 ffff880409b96420
>>> [   12.415547]  ffff8803ef979490 ffff880403ff4800 0000000000000000 ffff8800c926bac8
>>> [   12.415550] Call Trace:
>>> [   12.415555]  [<ffffffff8132e3e2>] dump_stack+0x4b/0x69
>>> [   12.415560]  [<ffffffff8105e386>] warn_slowpath_common+0x86/0xc0
>>> [   12.415563]  [<ffffffff8105e40c>] warn_slowpath_fmt+0x4c/0x50
>>> [   12.415566]  [<ffffffff8115f951>] account_page_cleaned+0x101/0x110
>>> [   12.415568]  [<ffffffff8115fa1d>] cancel_dirty_page+0xbd/0xf0
>>> [   12.415571]  [<ffffffff811fc044>] try_to_free_buffers+0x94/0xb0
>>> [   12.415575]  [<ffffffff81296740>] jbd2_journal_try_to_free_buffers+0x100/0x130
>>> [   12.415578]  [<ffffffff812498b2>] ext4_releasepage+0x52/0xa0
>>> [   12.415582]  [<ffffffff81153765>] try_to_release_page+0x35/0x50
>>> [   12.415585]  [<ffffffff811fcc13>] block_invalidatepage+0x113/0x130
>>> [   12.415587]  [<ffffffff81249d5e>] ext4_invalidatepage+0x5e/0xb0
>>> [   12.415590]  [<ffffffff8124a6f0>] ext4_da_invalidatepage+0x40/0x310
>>> [   12.415593]  [<ffffffff81162b03>] truncate_inode_page+0x83/0x90
>>> [   12.415595]  [<ffffffff81162ce9>] truncate_inode_pages_range+0x199/0x730
>>> [   12.415598]  [<ffffffff8109c494>] ? __wake_up+0x44/0x50
>>> [   12.415600]  [<ffffffff812962ca>] ? jbd2_journal_stop+0x1ba/0x3b0
>>> [   12.415603]  [<ffffffff8125a754>] ? ext4_unlink+0x2f4/0x330
>>> [   12.415607]  [<ffffffff811eed3d>] ? __inode_wait_for_writeback+0x6d/0xc0
>>> [   12.415609]  [<ffffffff811632ec>] truncate_inode_pages_final+0x4c/0x60
>>> [   12.415612]  [<ffffffff81250736>] ext4_evict_inode+0x116/0x4c0
>>> [   12.415615]  [<ffffffff811e139c>] evict+0xbc/0x190
>>> [   12.415617]  [<ffffffff811e1d2d>] iput+0x17d/0x1e0
>>> [   12.415620]  [<ffffffff811d623b>] do_unlinkat+0x1ab/0x2b0
>>> [   12.415622]  [<ffffffff811d6cb6>] SyS_unlink+0x16/0x20
>>> [   12.415626]  [<ffffffff817d7f97>] entry_SYSCALL_64_fastpath+0x12/0x6a
>>> [   12.415628] ---[ end trace 6fba1ddd3d240e13 ]---
>>> [   12.418211] ------------[ cut here ]------------
>
> I'm not denying the issue, bug the WARNING splat isn't necessarily
> catching a problem.  The corresponding code comes from your debug patch:
> +		WARN_ONCE(__this_cpu_read(memcg->stat->count[MEM_CGROUP_STAT_DIRTY]) > (1UL<<30), "MEM_CGROUP_STAT_DIRTY bogus");
>
> This only checks a single cpu's counter, which can be negative.  The sum
> of all counters is what matters.
> Imagine:
> cpu1) dirty page: inc
> cpu2) clean page: dec
> The sum is properly zero, but cpu2 is -1, which will trigger the WARN.
>
> I'll look at the code and also see if I can reproduce the failure using
> mem_cgroup_read_stat() for all of the new WARNs.
>
> Did you notice if the global /proc/meminfo:Dirty count also underflowed?

Looks to be miscommunication between memcg dirty page accounting and
page migration.