Date:   Wed, 20 Apr 2022 12:58:05 -0400
From:   Kent Overstreet <kent.overstreet@...il.com>
To:     Michal Hocko <mhocko@...e.com>
Cc:     linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        linux-fsdevel@...r.kernel.org, roman.gushchin@...ux.dev,
        hannes@...xchg.org
Subject: Re: [PATCH 3/4] mm: Centralize & improve oom reporting in show_mem.c

On Wed, Apr 20, 2022 at 08:58:36AM +0200, Michal Hocko wrote:
> On Tue 19-04-22 16:32:01, Kent Overstreet wrote:
> > This patch:
> >  - Moves lib/show_mem.c to mm/show_mem.c
> 
> Sure, why not. Should be a separate patch.
> 
> >  - Changes show_mem() to always report on slab usage
> >  - Instead of reporting on all slabs, we only report on top 10 slabs,
> >    and in sorted order
> >  - Also reports on shrinkers, with the new shrinkers_to_text().
> 
> Why do we need/want this? It would be also great to provide an example
> of why the new output is better (in which cases) than the existing one.

Did you read the cover letter to the patch series?

But sure, I can give you an example of the new output:

00177 018: page allocation failure: order:5, mode:0x40dc0(GFP_KERNEL|__GFP_COMP|__GFP_ZERO), nodemask=(null)
00177 CPU: 0 PID: 32171 Comm: 018 Not tainted 5.17.0-01346-g09b56740d418-dirty #154
00177 Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.15.0-1 04/01/2014
00177 Call Trace:
00177  <TASK>
00177  dump_stack_lvl+0x38/0x49
00177  dump_stack+0x10/0x12
00177  warn_alloc+0x128/0x150
00177  ? __alloc_pages_direct_compact+0x171/0x1f0
00177  __alloc_pages_slowpath.constprop.0+0xac6/0xc30
00177  ? make_kgid+0x17/0x20
00177  ? p9pdu_readf+0x28c/0xb00
00177  __alloc_pages+0x215/0x230
00177  kmalloc_order+0x30/0x80
00177  kmalloc_order_trace+0x1d/0x80
00177  __kmalloc+0x1a2/0x1d0
00177  v9fs_alloc_rdir_buf.isra.0+0x28/0x40
00177  v9fs_dir_readdir_dotl+0x55/0x160
00177  ? __alloc_pages+0x151/0x230
00177  ? lru_cache_add+0x1c/0x20
00177  ? lru_cache_add_inactive_or_unevictable+0x27/0x80
00177  ? __handle_mm_fault+0x666/0xae0
00177  iterate_dir+0x151/0x1b0
00177  __x64_sys_getdents64+0x80/0x120
00177  ? compat_fillonedir+0x160/0x160
00177  do_syscall_64+0x35/0x80
00177  entry_SYSCALL_64_after_hwframe+0x44/0xae
00177 RIP: 0033:0x7f0b15e2f9c7
00177 Code: 00 00 0f 05 eb b3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 00 48 81 fa ff ff ff 7f b8 ff ff ff 7f 48 0f 47 d0 b8 d9 00 00 00 0f 05 <48> 3d 00 f0 ff ff 77 01 c3 48 8b 15 79 b4 10 00 f7 d8 64 89 02 48
00177 RSP: 002b:00007ffcf9445b88 EFLAGS: 00000293 ORIG_RAX: 00000000000000d9
00177 RAX: ffffffffffffffda RBX: 000056137dd23ba0 RCX: 00007f0b15e2f9c7
00177 RDX: 000000000001f000 RSI: 000056137dd23bd0 RDI: 0000000000000003
00177 RBP: 000056137dd23bd0 R08: 0000000000000030 R09: 00007f0b15f3bc00
00177 R10: fffffffffffff776 R11: 0000000000000293 R12: ffffffffffffff88
00177 R13: 000056137dd23ba4 R14: 0000000000000000 R15: 000056137dd23ba0
00177  </TASK>
00177 Mem-Info:
00177 active_anon:13706 inactive_anon:32266 isolated_anon:16
00177  active_file:1653 inactive_file:1822 isolated_file:0
00177  unevictable:0 dirty:0 writeback:0
00177  slab_reclaimable:6242 slab_unreclaimable:11168
00177  mapped:3824 shmem:3 pagetables:1266 bounce:0
00177  kernel_misc_reclaimable:0
00177  free:4362 free_pcp:35 free_cma:0
00177 Node 0 active_anon:54824kB inactive_anon:129064kB active_file:6612kB inactive_file:7288kB unevictable:0kB isolated(anon):64kB isolated(file):0kB mapped:15296kB dirty:0kB writeback:0kB shmem:12kB writeback_tmp:0kB kernel_stack:3392kB pagetables:5064kB all_unreclaimable? no
00177 DMA free:2232kB boost:0kB min:88kB low:108kB high:128kB reserved_highatomic:0KB active_anon:2924kB inactive_anon:6596kB active_file:428kB inactive_file:384kB unevictable:0kB writepending:0kB present:15992kB managed:15360kB mlocked:0kB bounce:0kB free_pcp:0kB local_pcp:0kB free_cma:0kB
00177 lowmem_reserve[]: 0 426 426 426
00177 DMA32 free:15092kB boost:5836kB min:8432kB low:9080kB high:9728kB reserved_highatomic:0KB active_anon:52196kB inactive_anon:122392kB active_file:6176kB inactive_file:7068kB unevictable:0kB writepending:0kB present:507760kB managed:441816kB mlocked:0kB bounce:0kB free_pcp:72kB local_pcp:0kB free_cma:0kB
00177 lowmem_reserve[]: 0 0 0 0
00177 DMA: 284*4kB (UM) 53*8kB (UM) 21*16kB (U) 11*32kB (U) 0*64kB 0*128kB 0*256kB 0*512kB 0*1024kB 0*2048kB 0*4096kB = 2248kB
00177 DMA32: 2765*4kB (UME) 375*8kB (UME) 57*16kB (UM) 5*32kB (U) 0*64kB 0*128kB 0*256kB 0*512kB 0*1024kB 0*2048kB 0*4096kB = 15132kB
00177 4656 total pagecache pages
00177 1031 pages in swap cache
00177 Swap cache stats: add 6572399, delete 6572173, find 488603/3286476
00177 Free swap  = 509112kB
00177 Total swap = 2097148kB
00177 130938 pages RAM
00177 0 pages HighMem/MovableOnly
00177 16644 pages reserved
00177 Unreclaimable slab info:
00177 9p-fcall-cache    total: 8.25 MiB active: 8.25 MiB
00177 kernfs_node_cache total: 2.15 MiB active: 2.15 MiB
00177 kmalloc-64        total: 2.08 MiB active: 2.07 MiB
00177 task_struct       total: 1.95 MiB active: 1.95 MiB
00177 kmalloc-4k        total: 1.50 MiB active: 1.50 MiB
00177 signal_cache      total: 1.34 MiB active: 1.34 MiB
00177 kmalloc-2k        total: 1.16 MiB active: 1.16 MiB
00177 bch_inode_info    total: 1.02 MiB active: 922 KiB
00177 perf_event        total: 1.02 MiB active: 1.02 MiB
00177 biovec-max        total: 992 KiB active: 960 KiB
00177 Shrinkers:
00177 super_cache_scan: objects: 127
00177 super_cache_scan: objects: 106
00177 jbd2_journal_shrink_scan: objects: 32
00177 ext4_es_scan: objects: 32
00177 bch2_btree_cache_scan: objects: 8
00177   nr nodes:          24
00177   nr dirty:          0
00177   cannibalize lock:  0000000000000000
00177 
00177 super_cache_scan: objects: 8
00177 super_cache_scan: objects: 1

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