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Date:   Fri, 13 Jan 2023 11:57:16 -0800
From:   Mike Kravetz <mike.kravetz@oracle.com>
To:     Sergey Senozhatsky <senozhatsky@chromium.org>
Cc:     Minchan Kim <minchan@kernel.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        linux-kernel@vger.kernel.org, linux-mm@kvack.org
Subject: Re: [PATCHv2 0/4] zsmalloc: make zspage chain size configurable
Message-ID: <Y8G3nJ9+k2lB0kas@monkey>
References: <20230109033838.2779902-1-senozhatsky@chromium.org>
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On 01/09/23 12:38, Sergey Senozhatsky wrote:
> Hi,
> 
> 	This turns hard coded limit on maximum number of physical
> pages per-zspage into a config option. It also increases the default
> limit from 4 to 8.
> 
> Sergey Senozhatsky (4):
>   zsmalloc: rework zspage chain size selection
>   zsmalloc: skip chain size calculation for pow_of_2 classes
>   zsmalloc: make zspage chain size configurable
>   zsmalloc: set default zspage chain size to 8
> 
>  Documentation/mm/zsmalloc.rst | 168 ++++++++++++++++++++++++++++++++++
>  mm/Kconfig                    |  19 ++++
>  mm/zsmalloc.c                 |  72 +++++----------
>  3 files changed, 212 insertions(+), 47 deletions(-)

Hi Sergey,

The following BUG shows up after this series in linux-next.  I can easily
recreate by doing the following:

# echo large_value > /sys/kernel/mm/hugepages/hugepages-2048kB/nr_hugepages
where 'large_value' is a so big that there could never possibly be that
many 2MB huge pages in the system.

-- 
Mike Kravetz

[   22.981684] ------------[ cut here ]------------
[   22.982990] kernel BUG at mm/zsmalloc.c:1982!
[   22.984204] invalid opcode: 0000 [#1] PREEMPT SMP PTI
[   22.985561] CPU: 0 PID: 41 Comm: kcompactd0 Not tainted 6.2.0-rc3+ #13
[   22.987430] Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.1-2.fc37 04/01/2014
[   22.989728] RIP: 0010:zs_page_migrate+0x43c/0x490
[   22.991070] Code: c7 c6 c8 f6 21 82 e8 b3 73 f6 ff 0f 0b 0f 1f 44 00 00 e9 20 fd ff ff 0f 1f 44 00 00 e9 9e fd ff ff 48 83 ef 01 e9 6b fe ff ff <0f> 0b 48 8b 43 20 49 89 45 20 e9 ff fd ff ff 48 c7 c6 60 d3 1d 82
[   22.995900] RSP: 0018:ffffc9000121fb20 EFLAGS: 00010246
[   22.997364] RAX: 0000000000000002 RBX: ffffea0005b8b380 RCX: 0000000000000000
[   22.999299] RDX: 0000000000000002 RSI: ffffffff81e28a62 RDI: 00000000ffffffff
[   23.001236] RBP: ffff88816e2cf000 R08: ffffea0005b8b340 R09: 0000000000000008
[   23.003181] R10: ffff88827fffafe0 R11: 0000000000280000 R12: ffff88816e2cf400
[   23.005038] R13: ffffea0009e7f800 R14: ffff88817d783880 R15: ffff8881036a44d8
[   23.006921] FS:  0000000000000000(0000) GS:ffff888277c00000(0000) knlGS:0000000000000000
[   23.009116] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[   23.010732] CR2: 00007f8b14e20550 CR3: 0000000103026004 CR4: 0000000000370ef0
[   23.013978] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
[   23.015931] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
[   23.017892] Call Trace:
[   23.018664]  <TASK>
[   23.019345]  move_to_new_folio+0x14d/0x1f0
[   23.020710]  migrate_pages+0xe36/0x1240
[   23.021895]  ? __pfx_compaction_alloc+0x10/0x10
[   23.023202]  ? _raw_write_lock+0x13/0x30
[   23.024335]  ? __pfx_compaction_free+0x10/0x10
[   23.025608]  ? isolate_movable_page+0xff/0x250
[   23.026880]  compact_zone+0x9da/0xdf0
[   23.027990]  kcompactd_do_work+0x1d2/0x2c0
[   23.029180]  kcompactd+0x220/0x3e0
[   23.030166]  ? __pfx_autoremove_wake_function+0x10/0x10
[   23.031612]  ? __pfx_kcompactd+0x10/0x10
[   23.032706]  kthread+0xe6/0x110
[   23.033648]  ? __pfx_kthread+0x10/0x10
[   23.034704]  ret_from_fork+0x29/0x50
[   23.035734]  </TASK>
[   23.036443] Modules linked in: rfkill ip6table_filter ip6_tables sunrpc snd_hda_codec_generic snd_hda_intel snd_intel_dspcfg snd_hda_codec snd_hwdep snd_hda_core snd_seq snd_seq_device 9p netfs snd_pcm joydev 9pnet_virtio virtio_balloon snd_timer snd soundcore 9pnet virtio_blk virtio_net net_failover failover virtio_console crct10dif_pclmul crc32_pclmul crc32c_intel ghash_clmulni_intel serio_raw virtio_pci virtio virtio_pci_legacy_dev virtio_pci_modern_dev virtio_ring fuse
[   23.049869] ---[ end trace 0000000000000000 ]---
[   23.051154] RIP: 0010:zs_page_migrate+0x43c/0x490
[   23.052466] Code: c7 c6 c8 f6 21 82 e8 b3 73 f6 ff 0f 0b 0f 1f 44 00 00 e9 20 fd ff ff 0f 1f 44 00 00 e9 9e fd ff ff 48 83 ef 01 e9 6b fe ff ff <0f> 0b 48 8b 43 20 49 89 45 20 e9 ff fd ff ff 48 c7 c6 60 d3 1d 82
[   23.057413] RSP: 0018:ffffc9000121fb20 EFLAGS: 00010246
[   23.058892] RAX: 0000000000000002 RBX: ffffea0005b8b380 RCX: 0000000000000000
[   23.060867] RDX: 0000000000000002 RSI: ffffffff81e28a62 RDI: 00000000ffffffff
[   23.062835] RBP: ffff88816e2cf000 R08: ffffea0005b8b340 R09: 0000000000000008
[   23.064825] R10: ffff88827fffafe0 R11: 0000000000280000 R12: ffff88816e2cf400
[   23.066806] R13: ffffea0009e7f800 R14: ffff88817d783880 R15: ffff8881036a44d8
[   23.068738] FS:  0000000000000000(0000) GS:ffff888277c00000(0000) knlGS:0000000000000000
[   23.071022] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[   23.072579] CR2: 00007f8b14e20550 CR3: 0000000103026004 CR4: 0000000000370ef0
[   23.076152] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
[   23.078172] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
[   23.080134] note: kcompactd0[41] exited with preempt_count 1