Re: WARNINGs in set_task_reclaim_state with memory cgroup and full memory usage

[Yafang Shao]

On Sat, Aug 24, 2019 at 10:57 AM Hillf Danton <hdanton@xxxxxxxx> wrote:
>
>
> On Fri, 23 Aug 2019 18:00:15 -0400 Adric Blake wrote:
> > Synopsis:
> > A WARN_ON_ONCE is hit twice in set_task_reclaim_state under the
> > following conditions:
> > - a memory cgroup has been created and a task assigned it it
> > - memory.limit_in_bytes has been set
> > - memory has filled up, likely from cache
> >
> Thanks for report.
>
> > In my usage, I create a cgroup under the current session scope and
> > assign a task to it. I then set memory.limit_in_bytes and
> > memory.soft_limit_in_bytes for the cgroup to reasonable values, say
> > 1G/512M. The program accesses large files frequently and gradually
> > fills memory with the page cache. The warnings appears when the
> > entirety of the system memory is filled, presumably from other
> > programs.
> >
> > If I wait until the program has filled the entirety of system memory
> > with cache and then assign a memory limit, the warnings appear
> > immediately.
> >
> > I am building the linux git. I first noticed this issue with the
> > drm-tip 5.3rc3 and 5.3rc4 kernels, and tested linux master after
> > 5.3rc5 to confirm the bug more resoundingly.
> >
> > Here are the warnings.
> >
> > [38491.963105] WARNING: CPU: 7 PID: 175 at mm/vmscan.c:245 set_task_reclaim_state+0x1e/0x40
> > [38491.963106] Modules linked in: iwlmvm mac80211 libarc4 iwlwifi
> > cfg80211 xt_comment nls_iso8859_1 nls_cp437 vfat fat xfs jfs btrfs xor
> > raid6_pq libcrc32c ccm tun rfcomm fuse xt_tcpudp ip6t_REJECT
> > nf_reject_ipv6 ipt_REJECT nf_reject_ipv4 xt_multiport xt_owner
> > snd_hda_codec_hdmi ip6table_filter ip6_tables iptable_filter bnep ext4
> > crc32c_generic mbcache jbd2 snd_hda_codec_realtek
> > snd_hda_codec_generic snd_soc_skl snd_soc_hdac_hda snd_hda_ext_core
> > snd_soc_skl_ipc x86_pkg_temp_thermal intel_powerclamp snd_soc_sst_ipc
> > coretemp snd_soc_sst_dsp snd_soc_acpi_intel_match kvm_intel
> > snd_soc_acpi i915 snd_soc_core kvm snd_compress ac97_bus
> > snd_pcm_dmaengine snd_hda_intel i2c_algo_bit btusb irqbypass
> > drm_kms_helper btrtl snd_hda_codec dell_laptop btbcm crct10dif_pclmul
> > snd_hda_core crc32c_intel btintel iTCO_wdt ghash_clmulni_intel drm
> > ledtrig_audio aesni_intel iTCO_vendor_support snd_hwdep dell_wmi
> > rtsx_usb_ms r8169 dell_smbios aes_x86_64 mei_hdcp crypto_simd
> > intel_gtt bluetooth snd_pcm cryptd dcdbas
> > [38491.963155]  wmi_bmof dell_wmi_descriptor intel_rapl_msr
> > glue_helper snd_timer joydev intel_cstate snd realtek memstick
> > dell_smm_hwmon mousedev psmouse input_leds libphy intel_uncore
> > ecdh_generic ecc crc16 rfkill intel_rapl_perf soundcore i2c_i801
> > agpgart mei_me tpm_crb syscopyarea sysfillrect sysimgblt mei
> > intel_xhci_usb_role_switch fb_sys_fops idma64 tpm_tis roles
> > processor_thermal_device intel_rapl_common i2c_hid tpm_tis_core
> > int3403_thermal intel_soc_dts_iosf battery wmi intel_lpss_pci
> > intel_lpss intel_pch_thermal tpm int3400_thermal int3402_thermal
> > acpi_thermal_rel int340x_thermal_zone rng_core intel_hid ac
> > sparse_keymap evdev mac_hid crypto_user ip_tables x_tables
> > hid_multitouch rtsx_usb_sdmmc mmc_core rtsx_usb hid_logitech_hidpp
> > sr_mod cdrom sd_mod uas usb_storage hid_logitech_dj hid_generic usbhid
> > hid ahci serio_raw libahci atkbd libps2 libata xhci_pci scsi_mod
> > xhci_hcd crc32_pclmul i8042 serio f2fs [last unloaded: cfg80211]
> > [38491.963221] CPU: 7 PID: 175 Comm: kswapd0 Not tainted 5.3.0-rc5+149+gbb7ba8069de9 #1
> > [38491.963222] Hardware name: Dell Inc. Inspiron 5570/09YTN7, BIOS 1.2.3 05/15/2019
> > [38491.963226] RIP: 0010:set_task_reclaim_state+0x1e/0x40
> > [38491.963228] Code: 78 a9 e7 ff 0f 1f 84 00 00 00 00 00 0f 1f 44 00
> > 00 55 48 89 f5 53 48 89 fb 48 85 ed 48 8b 83 08 08 00 00 74 11 48 85
> > c0 74 02 <0f> 0b 48 89 ab 08 08 00 00 5b 5d c3 48 85 c0 75 f1 0f 0b 48
> > 89 ab
> > [38491.963229] RSP: 0018:ffff8c898031fc60 EFLAGS: 00010286
> > [38491.963230] RAX: ffff8c898031fe28 RBX: ffff892aa04ddc40 RCX: 0000000000000000
> > [38491.963231] RDX: ffff8c898031fc60 RSI: ffff8c898031fcd0 RDI: ffff892aa04ddc40
> > [38491.963233] RBP: ffff8c898031fcd0 R08: ffff8c898031fd48 R09: ffff89279674b800
> > [38491.963234] R10: 00000000ffffffff R11: 0000000000000000 R12: ffff8c898031fd48
> > [38491.963235] R13: ffff892a842ef000 R14: ffff892aaf7fc000 R15: 0000000000000000
> > [38491.963236] FS:  0000000000000000(0000) GS:ffff892aa33c0000(0000) knlGS:0000000000000000
> > [38491.963238] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> > [38491.963239] CR2: 00007f90628fa000 CR3: 000000027ee0a002 CR4: 00000000003606e0
> > [38491.963239] Call Trace:
> > [38491.963246]  mem_cgroup_shrink_node+0x9b/0x1d0
> > [38491.963250]  mem_cgroup_soft_limit_reclaim+0x10c/0x3a0
> > [38491.963254]  balance_pgdat+0x276/0x540
> > [38491.963258]  kswapd+0x200/0x3f0
> > [38491.963261]  ? wait_woken+0x80/0x80
> > [38491.963265]  kthread+0xfd/0x130
> > [38491.963267]  ? balance_pgdat+0x540/0x540
> > [38491.963269]  ? kthread_park+0x80/0x80
> > [38491.963273]  ret_from_fork+0x35/0x40
> > [38491.963276] ---[ end trace 727343df67b2398a ]---
>
> Save and restore reclaim state for global reclaimer as it
> can be clobbered by memcg.
>

Hi Hillf,

Thanks for your patch. It could fix this issue.
But I'm wondering if it is proper to place a new scan_control in
mem_cgroup_shrink_node().
Because the page alloction context is stored in the original
scan_control, but this new scan_control beaks it at all.
For example, the sc.nodemask is the page allocation preferred node,
but it is override by the new scan_control, that may cause extra
useless page reclaim, especially in the direct reclaim path.

Thanks
Yafang
> --- a/mm/vmscan.c
> +++ b/bb/vmscan.c
> @@ -253,6 +253,22 @@ static void set_task_reclaim_state(struc
>         task->reclaim_state = rs;
>  }
>
> +static struct reclaim_state *
> +save_task_reclaim_state(struct task_struct *task)
> +{
> +       struct reclaim_state *rs = task->reclaim_state;
> +       if (rs)
> +               set_task_reclaim_state(task, NULL);
> +       return rs;
> +}
> +
> +static void restore_task_reclaim_state(struct task_struct *task,
> +                                       struct reclaim_state *rs)
> +{
> +       if (rs)
> +               set_task_reclaim_state(task, rs);
> +}
> +
>  #ifdef CONFIG_MEMCG
>  static bool global_reclaim(struct scan_control *sc)
>  {
> @@ -3241,7 +3257,9 @@ unsigned long mem_cgroup_shrink_node(str
>                 .may_shrinkslab = 1,
>         };
>         unsigned long lru_pages;
> +       struct reclaim_state *rs;
>
> +       rs = save_task_reclaim_state(current);
>         set_task_reclaim_state(current, &sc.reclaim_state);
>         sc.gfp_mask = (gfp_mask & GFP_RECLAIM_MASK) |
>                         (GFP_HIGHUSER_MOVABLE & ~GFP_RECLAIM_MASK);
> @@ -3261,6 +3279,7 @@ unsigned long mem_cgroup_shrink_node(str
>         trace_mm_vmscan_memcg_softlimit_reclaim_end(sc.nr_reclaimed);
>
>         set_task_reclaim_state(current, NULL);
> +       restore_task_reclaim_state(current, rs);
>         *nr_scanned = sc.nr_scanned;
>
>         return sc.nr_reclaimed;
> --
>