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SubjectOver-eager swapping
We run a number of relatively large x86-64 hosts with twenty or so qemu-kvm
virtual machines on each of them, and I'm have some trouble with over-eager
swapping on some of the machines. This is resulting in load spikes during the
swapping and customer reports of very poor response latency from the virtual
machines which have been swapped out, despite the hosts apparently having
large amounts of free memory, and running fine if swap is turned off.


All of the hosts are currently running a 3.1.4 or 3.2.2 kernel and have ksm
enabled with 64GB of RAM and 2x eight-core AMD Opteron 6128 processors.
However, we have seen this same problem since 2010 on a 2.6.32.7 kernel and
older hardware - see http://marc.info/?l=linux-mm&m=128075337008943
(previous helpful contributors cc:ed here - thanks).

We have /proc/sys/vm/swappiness set to 0. The kernel config is here:
http://users.org.uk/config-3.1.4


The rrd graphs at http://imgur.com/a/Fklxr show a typical incident.

We estimate memory used from /proc/meminfo as:

= MemTotal - MemFree - Buffers + SwapTotal - SwapFree

The first rrd shows memory used increasing as a VM starts, but not getting
near the 64GB of physical RAM.

The second rrd shows the heavy swapping this VM start caused.

The third rrd shows a multi-gigabyte jump in swap used = SwapTotal - SwapFree

The fourth rrd shows the large load spike (from 1 to 15) caused by this swap
storm.


It is obviously hard to capture all of the relevant data actually during an
incident. However, as of this morning, the relevant stats are as below.

Any help much appreciated! Our strong belief is that there is unnecessary
swapping going on here, and causing these load spikes. We would like to run
with swap for real out-of-memory situations, but at present it is causing
these kind of load spikes on machines which run completely happily with swap
disabled.

Thanks,

Richard.


# cat /proc/meminfo
MemTotal: 65915384 kB
MemFree: 271104 kB
Buffers: 36274368 kB
Cached: 31048 kB
SwapCached: 1830860 kB
Active: 30594144 kB
Inactive: 32295972 kB
Active(anon): 21883428 kB
Inactive(anon): 4695308 kB
Active(file): 8710716 kB
Inactive(file): 27600664 kB
Unevictable: 6740 kB
Mlocked: 6740 kB
SwapTotal: 33054708 kB
SwapFree: 30067948 kB
Dirty: 1044 kB
Writeback: 0 kB
AnonPages: 24962708 kB
Mapped: 7320 kB
Shmem: 48 kB
Slab: 2210964 kB
SReclaimable: 1013272 kB
SUnreclaim: 1197692 kB
KernelStack: 6816 kB
PageTables: 129248 kB
NFS_Unstable: 0 kB
Bounce: 0 kB
WritebackTmp: 0 kB
CommitLimit: 66012400 kB
Committed_AS: 67375852 kB
VmallocTotal: 34359738367 kB
VmallocUsed: 259380 kB
VmallocChunk: 34308695568 kB
HardwareCorrupted: 0 kB
AnonHugePages: 155648 kB
HugePages_Total: 0
HugePages_Free: 0
HugePages_Rsvd: 0
HugePages_Surp: 0
Hugepagesize: 2048 kB
DirectMap4k: 576 kB
DirectMap2M: 2095104 kB
DirectMap1G: 65011712 kB

# cat /proc/sys/vm/zone_reclaim_mode
0

# cat /proc/sys/vm/min_unmapped_ratio
1

# cat /proc/slabinfo
slabinfo - version: 2.1
# name <active_objs> <num_objs> <objsize> <objperslab> <pagesperslab> : tunables <limit> <batchcount> <sharedfactor> : slabdata <active_slabs> <num_slabs> <sharedavail>
ext4_groupinfo_1k 32 32 128 32 1 : tunables 0 0 0 : slabdata 1 1 0
RAWv6 34 34 960 34 8 : tunables 0 0 0 : slabdata 1 1 0
UDPLITEv6 0 0 960 34 8 : tunables 0 0 0 : slabdata 0 0 0
UDPv6 544 544 960 34 8 : tunables 0 0 0 : slabdata 16 16 0
tw_sock_TCPv6 0 0 320 25 2 : tunables 0 0 0 : slabdata 0 0 0
TCPv6 72 72 1728 18 8 : tunables 0 0 0 : slabdata 4 4 0
nf_conntrack_expect 592 592 216 37 2 : tunables 0 0 0 : slabdata 16 16 0
nf_conntrack_ffffffff8199a280 933 1856 280 29 2 : tunables 0 0 0 : slabdata 64 64 0
dm_raid1_read_record 0 0 1064 30 8 : tunables 0 0 0 : slabdata 0 0 0
dm_snap_pending_exception 0 0 104 39 1 : tunables 0 0 0 : slabdata 0 0 0
dm_crypt_io 1811 2574 152 26 1 : tunables 0 0 0 : slabdata 99 99 0
kcopyd_job 0 0 3240 10 8 : tunables 0 0 0 : slabdata 0 0 0
dm_uevent 0 0 2608 12 8 : tunables 0 0 0 : slabdata 0 0 0
cfq_queue 0 0 232 35 2 : tunables 0 0 0 : slabdata 0 0 0
bsg_cmd 0 0 312 26 2 : tunables 0 0 0 : slabdata 0 0 0
mqueue_inode_cache 36 36 896 36 8 : tunables 0 0 0 : slabdata 1 1 0
udf_inode_cache 0 0 656 24 4 : tunables 0 0 0 : slabdata 0 0 0
fuse_request 0 0 608 26 4 : tunables 0 0 0 : slabdata 0 0 0
fuse_inode 0 0 704 46 8 : tunables 0 0 0 : slabdata 0 0 0
ntfs_big_inode_cache 0 0 832 39 8 : tunables 0 0 0 : slabdata 0 0 0
ntfs_inode_cache 0 0 280 29 2 : tunables 0 0 0 : slabdata 0 0 0
isofs_inode_cache 0 0 600 27 4 : tunables 0 0 0 : slabdata 0 0 0
fat_inode_cache 0 0 664 24 4 : tunables 0 0 0 : slabdata 0 0 0
fat_cache 0 0 40 102 1 : tunables 0 0 0 : slabdata 0 0 0
hugetlbfs_inode_cache 28 28 568 28 4 : tunables 0 0 0 : slabdata 1 1 0
squashfs_inode_cache 0 0 640 25 4 : tunables 0 0 0 : slabdata 0 0 0
jbd2_journal_handle 2720 2720 24 170 1 : tunables 0 0 0 : slabdata 16 16 0
jbd2_journal_head 818 1620 112 36 1 : tunables 0 0 0 : slabdata 45 45 0
jbd2_revoke_record 2048 4096 32 128 1 : tunables 0 0 0 : slabdata 32 32 0
ext4_inode_cache 2754 5328 864 37 8 : tunables 0 0 0 : slabdata 144 144 0
ext4_xattr 0 0 88 46 1 : tunables 0 0 0 : slabdata 0 0 0
ext4_free_data 1168 2628 56 73 1 : tunables 0 0 0 : slabdata 36 36 0
ext4_allocation_context 540 540 136 30 1 : tunables 0 0 0 : slabdata 18 18 0
ext4_io_end 0 0 1128 29 8 : tunables 0 0 0 : slabdata 0 0 0
ext4_io_page 256 256 16 256 1 : tunables 0 0 0 : slabdata 1 1 0
configfs_dir_cache 0 0 88 46 1 : tunables 0 0 0 : slabdata 0 0 0
kioctx 0 0 384 42 4 : tunables 0 0 0 : slabdata 0 0 0
inotify_inode_mark 30 30 136 30 1 : tunables 0 0 0 : slabdata 1 1 0
kvm_async_pf 448 448 144 28 1 : tunables 0 0 0 : slabdata 16 16 0
kvm_vcpu 64 94 13856 2 8 : tunables 0 0 0 : slabdata 47 47 0
UDP-Lite 0 0 768 42 8 : tunables 0 0 0 : slabdata 0 0 0
xfrm_dst_cache 0 0 448 36 4 : tunables 0 0 0 : slabdata 0 0 0
ip_fib_trie 219 219 56 73 1 : tunables 0 0 0 : slabdata 3 3 0
arp_cache 417 500 320 25 2 : tunables 0 0 0 : slabdata 20 20 0
RAW 672 672 768 42 8 : tunables 0 0 0 : slabdata 16 16 0
UDP 672 672 768 42 8 : tunables 0 0 0 : slabdata 16 16 0
tw_sock_TCP 512 1088 256 32 2 : tunables 0 0 0 : slabdata 34 34 0
TCP 345 357 1536 21 8 : tunables 0 0 0 : slabdata 17 17 0
blkdev_queue 414 440 1616 20 8 : tunables 0 0 0 : slabdata 22 22 0
blkdev_requests 945 2209 344 47 4 : tunables 0 0 0 : slabdata 47 47 0
sock_inode_cache 456 475 640 25 4 : tunables 0 0 0 : slabdata 19 19 0
shmem_inode_cache 2063 2375 632 25 4 : tunables 0 0 0 : slabdata 95 95 0
Acpi-ParseExt 3848 3864 72 56 1 : tunables 0 0 0 : slabdata 69 69 0
Acpi-Namespace 633667 1059270 40 102 1 : tunables 0 0 0 : slabdata 10385 10385 0
task_delay_info 1238 1584 112 36 1 : tunables 0 0 0 : slabdata 44 44 0
taskstats 384 384 328 24 2 : tunables 0 0 0 : slabdata 16 16 0
proc_inode_cache 2460 3250 616 26 4 : tunables 0 0 0 : slabdata 125 125 0
sigqueue 400 400 160 25 1 : tunables 0 0 0 : slabdata 16 16 0
bdev_cache 701 714 768 42 8 : tunables 0 0 0 : slabdata 17 17 0
sysfs_dir_cache 31662 34425 80 51 1 : tunables 0 0 0 : slabdata 675 675 0
inode_cache 2546 3886 552 29 4 : tunables 0 0 0 : slabdata 134 134 0
dentry 9452 14868 192 42 2 : tunables 0 0 0 : slabdata 354 354 0
buffer_head 8175114 8360937 104 39 1 : tunables 0 0 0 : slabdata 214383 214383 0
vm_area_struct 35344 35834 176 46 2 : tunables 0 0 0 : slabdata 782 782 0
files_cache 736 874 704 46 8 : tunables 0 0 0 : slabdata 19 19 0
signal_cache 1011 1296 896 36 8 : tunables 0 0 0 : slabdata 36 36 0
sighand_cache 682 945 2112 15 8 : tunables 0 0 0 : slabdata 63 63 0
task_struct 1057 1386 1520 21 8 : tunables 0 0 0 : slabdata 66 66 0
anon_vma 2417 2856 72 56 1 : tunables 0 0 0 : slabdata 51 51 0
shared_policy_node 4877 6800 48 85 1 : tunables 0 0 0 : slabdata 80 80 0
numa_policy 45589 48450 24 170 1 : tunables 0 0 0 : slabdata 285 285 0
radix_tree_node 227192 248388 568 28 4 : tunables 0 0 0 : slabdata 9174 9174 0
idr_layer_cache 603 660 544 30 4 : tunables 0 0 0 : slabdata 22 22 0
dma-kmalloc-8192 0 0 8192 4 8 : 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-2048 0 0 2048 16 8 : tunables 0 0 0 : slabdata 0 0 0
dma-kmalloc-1024 0 0 1024 32 8 : tunables 0 0 0 : slabdata 0 0 0
dma-kmalloc-512 0 0 512 32 4 : tunables 0 0 0 : slabdata 0 0 0
dma-kmalloc-256 0 0 256 32 2 : 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-64 0 0 64 64 1 : 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-16 0 0 16 256 1 : 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-192 0 0 192 42 2 : tunables 0 0 0 : slabdata 0 0 0
dma-kmalloc-96 0 0 96 42 1 : tunables 0 0 0 : slabdata 0 0 0
kmalloc-8192 88 100 8192 4 8 : tunables 0 0 0 : slabdata 25 25 0
kmalloc-4096 3567 3704 4096 8 8 : tunables 0 0 0 : slabdata 463 463 0
kmalloc-2048 55140 55936 2048 16 8 : tunables 0 0 0 : slabdata 3496 3496 0
kmalloc-1024 5960 6496 1024 32 8 : tunables 0 0 0 : slabdata 203 203 0
kmalloc-512 12185 12704 512 32 4 : tunables 0 0 0 : slabdata 397 397 0
kmalloc-256 195078 199040 256 32 2 : tunables 0 0 0 : slabdata 6220 6220 0
kmalloc-128 45645 47328 128 32 1 : tunables 0 0 0 : slabdata 1479 1479 0
kmalloc-64 14647251 14776576 64 64 1 : tunables 0 0 0 : slabdata 230884 230884 0
kmalloc-32 5573 7552 32 128 1 : tunables 0 0 0 : slabdata 59 59 0
kmalloc-16 7550 10752 16 256 1 : tunables 0 0 0 : slabdata 42 42 0
kmalloc-8 13805 14848 8 512 1 : tunables 0 0 0 : slabdata 29 29 0
kmalloc-192 47641 50883 192 42 2 : tunables 0 0 0 : slabdata 1214 1214 0
kmalloc-96 3673 6006 96 42 1 : tunables 0 0 0 : slabdata 143 143 0
kmem_cache 32 32 256 32 2 : tunables 0 0 0 : slabdata 1 1 0
kmem_cache_node 495 576 64 64 1 : tunables 0 0 0 : slabdata 9 9 0

# cat /proc/buddyinfo
Node 0, zone DMA 0 0 1 0 2 1 1 0 1 1 3
Node 0, zone DMA32 9148 1941 657 673 131 53 18 2 0 0 0
Node 0, zone Normal 8080 13 0 2 0 2 1 0 1 0 0
Node 1, zone Normal 19071 3239 675 200 413 37 4 1 2 0 0
Node 2, zone Normal 37716 3924 154 9 3 1 2 0 1 0 0
Node 3, zone Normal 20015 4590 1768 996 334 20 1 1 1 0 0

# grep MemFree /sys/devices/system/node/node*/meminfo
/sys/devices/system/node/node0/meminfo:Node 0 MemFree: 201460 kB
/sys/devices/system/node/node1/meminfo:Node 1 MemFree: 283224 kB
/sys/devices/system/node/node2/meminfo:Node 2 MemFree: 287060 kB
/sys/devices/system/node/node3/meminfo:Node 3 MemFree: 316928 kB

# cat /proc/vmstat
nr_free_pages 224933
nr_inactive_anon 1173838
nr_active_anon 5209232
nr_inactive_file 6998686
nr_active_file 2180311
nr_unevictable 1685
nr_mlock 1685
nr_anon_pages 5940145
nr_mapped 1836
nr_file_pages 9635092
nr_dirty 603
nr_writeback 0
nr_slab_reclaimable 253121
nr_slab_unreclaimable 299440
nr_page_table_pages 32311
nr_kernel_stack 854
nr_unstable 0
nr_bounce 0
nr_vmscan_write 50485772
nr_writeback_temp 0
nr_isolated_anon 0
nr_isolated_file 0
nr_shmem 12
nr_dirtied 5630347228
nr_written 5625041387
numa_hit 28372623283
numa_miss 4761673976
numa_foreign 4761673976
numa_interleave 30490
numa_local 28372334279
numa_other 4761962980
nr_anon_transparent_hugepages 76
nr_dirty_threshold 8192
nr_dirty_background_threshold 4096
pgpgin 9523143630
pgpgout 23124688920
pswpin 57978726
pswpout 50121412
pgalloc_dma 0
pgalloc_dma32 1132547190
pgalloc_normal 32421613044
pgalloc_movable 0
pgfree 39379011152
pgactivate 751722445
pgdeactivate 591205976
pgfault 41103638391
pgmajfault 11853858
pgrefill_dma 0
pgrefill_dma32 24124080
pgrefill_normal 540719764
pgrefill_movable 0
pgsteal_dma 0
pgsteal_dma32 297677595
pgsteal_normal 4784595717
pgsteal_movable 0
pgscan_kswapd_dma 0
pgscan_kswapd_dma32 241277864
pgscan_kswapd_normal 4004618399
pgscan_kswapd_movable 0
pgscan_direct_dma 0
pgscan_direct_dma32 65729843
pgscan_direct_normal 1012932822
pgscan_direct_movable 0
zone_reclaim_failed 0
pginodesteal 66
slabs_scanned 668153728
kswapd_steal 4063341017
kswapd_inodesteal 2063
kswapd_low_wmark_hit_quickly 9834
kswapd_high_wmark_hit_quickly 488468
kswapd_skip_congestion_wait 580150
pageoutrun 22006623
allocstall 926752
pgrotated 28467920
compact_blocks_moved 522323130
compact_pages_moved 5774251432
compact_pagemigrate_failed 5267247
compact_stall 121045
compact_fail 68349
compact_success 52696
htlb_buddy_alloc_success 0
htlb_buddy_alloc_fail 0
unevictable_pgs_culled 19976952
unevictable_pgs_scanned 0
unevictable_pgs_rescued 33137561
unevictable_pgs_mlocked 35042070
unevictable_pgs_munlocked 33138335
unevictable_pgs_cleared 0
unevictable_pgs_stranded 0
unevictable_pgs_mlockfreed 1024
thp_fault_alloc 263176
thp_fault_fallback 717335
thp_collapse_alloc 21307
thp_collapse_alloc_failed 91103
thp_split 90328


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