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? -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>