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SubjectRe: Kswapd in 3.2.0-rc5 is a CPU hog
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On Wed, 2011-12-21 at 11:24 +0100, Michal Hocko wrote:
> [Let's cc also some fs and xfs people]
>
> On Wed 21-12-11 14:15:21, nowhere wrote:
> > В Ср., 21/12/2011 в 10:52 +0100, Michal Hocko пишет:
> > > [Let's CC linux-mm]
> > >
> > > On Wed 21-12-11 07:10:36, Nikolay S. wrote:
> > > > Hello,
> > > >
> > > > I'm using 3.2-rc5 on a machine, which atm does almost nothing except
> > > > file system operations and network i/o (i.e. file server). And there is
> > > > a problem with kswapd.
> > >
> > > What kind of filesystem do you use?
> >
> > Well, that is XFS.
> > I have a large volume with ~200000 files, and a periodic job, which
> > checks all file's timestamps once per 30 minutes and makes actions if
> > timestamp has changed.
>
> Is it the first time you are seeing this? I am not familiar with xfs at
> all but the number of files sounds like dcache shrinker might be really
> busy...
>
> > > > I'm playing with dd:
> > > > dd if=/some/big/file of=/dev/null bs=8M


Just to be clear, is it always the same file you are
operating on in all of the cases you show here? If
so, there anything else happening to that file in
the mean time? Is it being written to at all?

Is the filesystem in question (the one with the
big file) also being NFS served? Are there any
other filesystems being served, and if so, are
they also XFS?

I presume you are doing nothing special with respect
to the file serving, i.e. in all these cases and
timings, etc. the system has been and continues to
act as an NFS server.

Is the filesystem anywhere near full?

I don't know if these answers change much but it
might help to complete the picture.

Thanks.

-Alex
> > > > I.e. I'm filling page cache.
> > > >
> > > > So when the machine is just rebooted, kswapd during this operation is
> > > > almost idle, just 5-8 percent according to top.
> > > >
> > > > After ~5 days of uptime (5 days, 2:10), the same operation demands ~70%
> > > > for kswapd:
> > > >
> > > > PID USER S %CPU %MEM TIME+ SWAP COMMAND
> > > > 420 root R 70 0.0 22:09.60 0 kswapd0
> > > > 17717 nowhere D 27 0.2 0:01.81 10m dd
> > > >
> > > > In fact, kswapd cpu usage on this operation steadily increases over
> > > > time.
> > > >
> > > > Also read performance degrades over time. After reboot:
> > > > dd if=/some/big/file of=/dev/null bs=8M
> > > > 1019+1 records in
> > > > 1019+1 records out
> > > > 8553494018 bytes (8.6 GB) copied, 16.211 s, 528 MB/s
> > > >
> > > > After ~5 days uptime:
> > > > dd if=/some/big/file of=/dev/null bs=8M
> > > > 1019+1 records in
> > > > 1019+1 records out
> > > > 8553494018 bytes (8.6 GB) copied, 29.0507 s, 294 MB/s
> > > >
> > > > Whereas raw disk sequential read performance stays the same:
> > > > dd if=/some/big/file of=/dev/null bs=8M iflag=direct
> > > > 1019+1 records in
> > > > 1019+1 records out
> > > > 8553494018 bytes (8.6 GB) copied, 14.7286 s, 581 MB/s
> > > >
> > > > Also after dropping caches, situation somehow improves, but not to the
> > > > state of freshly restarted system:
> > > > PID USER S %CPU %MEM TIME+ SWAP COMMAND
> > > > 420 root S 39 0.0 23:31.17 0 kswapd0
> > > > 19829 nowhere D 24 0.2 0:02.72 7764 dd
> > > >
> > > > perf shows:
> > > >
> > > > 31.24% kswapd0 [kernel.kallsyms] [k] _raw_spin_lock
> > > > 26.19% kswapd0 [kernel.kallsyms] [k] shrink_slab
> > > > 16.28% kswapd0 [kernel.kallsyms] [k] prune_super
> > > > 6.55% kswapd0 [kernel.kallsyms] [k] grab_super_passive
> > > > 5.35% kswapd0 [kernel.kallsyms] [k] down_read_trylock
> > > > 4.03% kswapd0 [kernel.kallsyms] [k] up_read
> > > > 2.31% kswapd0 [kernel.kallsyms] [k] put_super
> > > > 1.81% kswapd0 [kernel.kallsyms] [k] drop_super
> > > > 0.99% kswapd0 [kernel.kallsyms] [k] __put_super
> > > > 0.25% kswapd0 [kernel.kallsyms] [k] __isolate_lru_page
> > > > 0.23% kswapd0 [kernel.kallsyms] [k] free_pcppages_bulk
> > > > 0.19% kswapd0 [r8169] [k] rtl8169_interrupt
> > > > 0.15% kswapd0 [kernel.kallsyms] [k] twa_interrupt
> > >
> > > Quite a lot of time spent shrinking slab (dcache I guess) and a lot of
> > > spin lock contention.
> >
> > This is slabinfo, sorted by num objects:
> >
> > xfs_inode 192941 193205 960 17 4 : tunables 0 0 0 : slabdata 11365 11365 0
> > dentry 118818 118818 192 21 1 : tunables 0 0 0 : slabdata 5658 5658 0
> > kmalloc-256 107920 107920 256 16 1 : tunables 0 0 0 : slabdata 6745 6745 0
> > kmalloc-64 59912 102656 64 64 1 : tunables 0 0 0 : slabdata 1604 1604 0
> > radix_tree_node 30618 33474 568 14 2 : tunables 0 0 0 : slabdata 2391 2391 0
> > kmalloc-96 27092 41202 96 42 1 : tunables 0 0 0 : slabdata 981 981 0
> > buffer_head 24892 63843 104 39 1 : tunables 0 0 0 : slabdata 1637 1637 0
> > kmalloc-192 23332 34503 192 21 1 : tunables 0 0 0 : slabdata 1643 1643 0
> > sysfs_dir_cache 17444 17444 144 28 1 : tunables 0 0 0 : slabdata 623 623 0
> > arp_cache 12863 14796 320 12 1 : tunables 0 0 0 : slabdata 1233 1233 0
> > kmalloc-512 11051 11440 512 16 2 : tunables 0 0 0 : slabdata 715 715 0
> > kmalloc-128 10611 13152 128 32 1 : tunables 0 0 0 : slabdata 411 411 0
> > ext4_inode_cache 9660 18018 880 18 4 : tunables 0 0 0 : slabdata 1001 1001 0
> > kmalloc-8 8704 8704 8 512 1 : tunables 0 0 0 : slabdata 17 17 0
> > ext4_io_page 6912 6912 16 256 1 : tunables 0 0 0 : slabdata 27 27 0
> > anon_vma_chain 6701 10880 48 85 1 : tunables 0 0 0 : slabdata 128 128 0
> > Acpi-Namespace 6611 8058 40 102 1 : tunables 0 0 0 : slabdata 79 79 0
> > fsnotify_event_holder 6290 6970 24 170 1 : tunables 0 0 0 : slabdata 41 41 0
> > kmalloc-1024 5813 5888 1024 16 4 : tunables 0 0 0 : slabdata 368 368 0
> > vm_area_struct 5664 5664 168 24 1 : tunables 0 0 0 : slabdata 236 236 0
> > reiser_inode_cache 3992 5198 704 23 4 : tunables 0 0 0 : slabdata 226 226 0
> > Acpi-ParseExt 3808 3808 72 56 1 : tunables 0 0 0 : slabdata 68 68 0
> > kmalloc-2048 3587 3888 2048 16 8 : tunables 0 0 0 : slabdata 243 243 0
> > proc_inode_cache 3498 3510 624 13 2 : tunables 0 0 0 : slabdata 270 270 0
> > anon_vma 3380 3640 72 56 1 : tunables 0 0 0 : slabdata 65 65 0
> > kmalloc-16 3072 3072 16 256 1 : tunables 0 0 0 : slabdata 12 12 0
> > inode_cache 3024 3024 560 14 2 : tunables 0 0 0 : slabdata 216 216 0
> > ext4_allocation_context 3000 3000 136 30 1 : tunables 0 0 0 : slabdata 100 100 0
> > nf_conntrack_ffffffff81776d40 2910 3549 312 13 1 : tunables 0 0 0 : slabdata 273 273 0
> > kmalloc-4096 2792 3136 4096 8 8 : tunables 0 0 0 : slabdata 392 392 0
> > ext4_free_data 2701 2701 56 73 1 : tunables 0 0 0 : slabdata 37 37 0
> > pid_namespace 2130 2130 2112 15 8 : tunables 0 0 0 : slabdata 142 142 0
> > mqueue_inode_cache 2124 2124 896 18 4 : tunables 0 0 0 : slabdata 118 118 0
> > jbd2_revoke_record 1664 1664 32 128 1 : tunables 0 0 0 : slabdata 13 13 0
> > kmalloc-32 1434 3072 32 128 1 : tunables 0 0 0 : slabdata 24 24 0
> > shmem_inode_cache 1400 1521 624 13 2 : tunables 0 0 0 : slabdata 117 117 0
> > xfs_ili 1139 1260 216 18 1 : tunables 0 0 0 : slabdata 70 70 0
> > nfsd4_stateids 1131 1496 120 34 1 : tunables 0 0 0 : slabdata 44 44 0
> > idr_layer_cache 900 900 544 15 2 : tunables 0 0 0 : slabdata 60 60 0
> > jbd2_journal_head 742 1008 112 36 1 : tunables 0 0 0 : slabdata 28 28 0
> > fsnotify_event 648 648 112 36 1 : tunables 0 0 0 : slabdata 18 18 0
> > sock_inode_cache 577 624 640 12 2 : tunables 0 0 0 : slabdata 52 52 0
> > tw_sock_TCP 504 504 192 21 1 : tunables 0 0 0 : slabdata 24 24 0
> > TCP 356 414 1728 18 8 : tunables 0 0 0 : slabdata 23 23 0
> > RAW 342 342 832 19 4 : tunables 0 0 0 : slabdata 18 18 0
> > jbd2_journal_handle 340 340 24 170 1 : tunables 0 0 0 : slabdata 2 2 0
> > blkdev_requests 322 322 344 23 2 : tunables 0 0 0 : slabdata 14 14 0
> > task_struct 293 357 1504 21 8 : tunables 0 0 0 : slabdata 17 17 0
> > UDP 285 285 832 19 4 : tunables 0 0 0 : slabdata 15 15 0
> > files_cache 276 276 704 23 4 : tunables 0 0 0 : slabdata 12 12 0
> > nfsd4_openowners 220 320 392 20 2 : tunables 0 0 0 : slabdata 16 16 0
> > mm_struct 216 216 896 18 4 : tunables 0 0 0 : slabdata 12 12 0
> > sighand_cache 199 225 2112 15 8 : tunables 0 0 0 : slabdata 15 15 0
> > nfsd4_delegations 198 198 368 22 2 : tunables 0 0 0 : slabdata 9 9 0
> > kmem_cache_node 192 192 64 64 1 : tunables 0 0 0 : slabdata 3 3 0
> > xfs_buf_item 162 162 224 18 1 : tunables 0 0 0 : slabdata 9 9 0
> > ip_fib_trie 146 146 56 73 1 : tunables 0 0 0 : slabdata 2 2 0
> > ext4_io_end 140 154 1128 14 4 : tunables 0 0 0 : slabdata 11 11 0
> > dnotify_mark 120 120 136 30 1 : tunables 0 0 0 : slabdata 4 4 0
> > TCPv6 104 119 1856 17 8 : tunables 0 0 0 : slabdata 7 7 0
> > cfq_queue 102 102 232 17 1 : tunables 0 0 0 : slabdata 6 6 0
> > Acpi-State 102 102 80 51 1 : tunables 0 0 0 : slabdata 2 2 0
> > sigqueue 100 100 160 25 1 : tunables 0 0 0 : slabdata 4 4 0
> > xfs_efd_item 80 80 400 20 2 : tunables 0 0 0 : slabdata 4 4 0
> > tw_sock_TCPv6 64 144 256 16 1 : tunables 0 0 0 : slabdata 9 9 0
> > bdev_cache 57 57 832 19 4 : tunables 0 0 0 : slabdata 3 3 0
> > blkdev_queue 54 54 1744 18 8 : tunables 0 0 0 : slabdata 3 3 0
> > net_namespace 52 52 2432 13 8 : tunables 0 0 0 : slabdata 4 4 0
> > kmalloc-8192 52 52 8192 4 8 : tunables 0 0 0 : slabdata 13 13 0
> > kmem_cache 42 42 192 21 1 : tunables 0 0 0 : slabdata 2 2 0
> > xfs_log_ticket 40 40 200 20 1 : tunables 0 0 0 : slabdata 2 2 0
> > xfs_btree_cur 38 38 208 19 1 : tunables 0 0 0 : slabdata 2 2 0
> > rpc_inode_cache 38 38 832 19 4 : tunables 0 0 0 : slabdata 2 2 0
> > nf_conntrack_expect 34 34 240 17 1 : tunables 0 0 0 : slabdata 2 2 0
> > xfs_da_state 32 32 488 16 2 : tunables 0 0 0 : slabdata 2 2 0
> > UDPv6 32 32 1024 16 4 : tunables 0 0 0 : slabdata 2 2 0
> > xfs_trans 28 28 280 14 1 : tunables 0 0 0 : slabdata 2 2 0
> > taskstats 24 24 328 12 1 : tunables 0 0 0 : slabdata 2 2 0
> > dio 24 24 640 12 2 : tunables 0 0 0 : slabdata 2 2 0
> > posix_timers_cache 23 23 176 23 1 : tunables 0 0 0 : slabdata 1 1 0
> > hugetlbfs_inode_cache 14 14 560 14 2 : tunables 0 0 0 : slabdata 1 1 0
> > xfrm_dst_cache 0 0 384 21 2 : tunables 0 0 0 : slabdata 0 0 0
> > user_namespace 0 0 1072 15 4 : tunables 0 0 0 : slabdata 0 0 0
> > UDPLITEv6 0 0 1024 16 4 : tunables 0 0 0 : slabdata 0 0 0
> > UDP-Lite 0 0 832 19 4 : tunables 0 0 0 : slabdata 0 0 0
> > kcopyd_job 0 0 3240 10 8 : tunables 0 0 0 : slabdata 0 0 0
> > flow_cache 0 0 104 39 1 : tunables 0 0 0 : slabdata 0 0 0
> > ext2_xattr 0 0 88 46 1 : tunables 0 0 0 : slabdata 0 0 0
> > ext2_inode_cache 0 0 752 21 4 : tunables 0 0 0 : slabdata 0 0 0
> > dquot 0 0 256 16 1 : tunables 0 0 0 : slabdata 0 0 0
> > dm_uevent 0 0 2608 12 8 : tunables 0 0 0 : slabdata 0 0 0
> > dma-kmalloc-96 0 0 96 42 1 : tunables 0 0 0 : slabdata 0 0 0
> > dma-kmalloc-8192 0 0 8192 4 8 : tunables 0 0 0 : slabdata 0 0 0
> > dma-kmalloc-8 0 0 8 512 1 : tunables 0 0 0 : slabdata 0 0 0
> > dma-kmalloc-64 0 0 64 64 1 : tunables 0 0 0 : slabdata 0 0 0
> > dma-kmalloc-512 0 0 512 16 2 : tunables 0 0 0 : slabdata 0 0 0
> > dma-kmalloc-4096 0 0 4096 8 8 : tunables 0 0 0 : slabdata 0 0 0
> > dma-kmalloc-32 0 0 32 128 1 : tunables 0 0 0 : slabdata 0 0 0
> > dma-kmalloc-256 0 0 256 16 1 : tunables 0 0 0 : slabdata 0 0 0
> > dma-kmalloc-2048 0 0 2048 16 8 : tunables 0 0 0 : slabdata 0 0 0
> > dma-kmalloc-192 0 0 192 21 1 : tunables 0 0 0 : slabdata 0 0 0
> > dma-kmalloc-16 0 0 16 256 1 : tunables 0 0 0 : slabdata 0 0 0
> > dma-kmalloc-128 0 0 128 32 1 : tunables 0 0 0 : slabdata 0 0 0
> > dma-kmalloc-1024 0 0 1024 16 4 : tunables 0 0 0 : slabdata 0 0 0
> > bsg_cmd 0 0 312 13 1 : tunables 0 0 0 : slabdata 0 0 0
> >
> > > Could you also take few snapshots of /proc/420/stack to see what kswapd
> > > is doing.
> >
> > Uhm, there is no such entry in proc. Guess I need to enable some kernel
> > option and recompile?
>
> Yes, you need CONFIG_STACKTRACE. But you can get a similar information
> by sysrq+t
>
> > This will reset uptime and a problem for another 5-10 days..
>
> Then don't do that ;)
>
> > > > P.S.: The message above was written couple of days ago. Now I'm at 10
> > > > days uptime, and this is the result as of today
> > > > PID USER S %CPU %MEM TIME+ SWAP COMMAND
> > > > 420 root R 93 0.0 110:48.48 0 kswapd0
> > > > 30085 nowhere D 42 0.2 0:04.36 10m dd
> > > >
> > > > PPS: Please CC me.
>



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