Re: lot of MemAvailable but falling cache and raising PSI

[Stefan Priebe - Profihost AG <s.priebe@profihost.ag>]

These are the biggest differences in meminfo before and after cached
starts to drop. I didn't expect cached end up in MemFree.

Before:
MemTotal:       16423116 kB
MemFree:          374572 kB
MemAvailable:    5633816 kB
Cached:          5550972 kB
Inactive:        4696580 kB
Inactive(file):  3624776 kB


After:
MemTotal:       16423116 kB
MemFree:         3477168 kB
MemAvailable:    6066916 kB
Cached:          2724504 kB
Inactive:        1854740 kB
Inactive(file):   950680 kB

Any explanation?

Greets,
Stefan
Am 05.09.19 um 13:56 schrieb Stefan Priebe - Profihost AG:
> 
> Am 05.09.19 um 13:40 schrieb Michal Hocko:
>> On Thu 05-09-19 13:27:10, Stefan Priebe - Profihost AG wrote:
>>> Hello all,
>>>
>>> i hope you can help me again to understand the current MemAvailable
>>> value in the linux kernel. I'm running a 4.19.52 kernel + psi patches in
>>> this case.
>>>
>>> I'm seeing the following behaviour i don't understand and ask for help.
>>>
>>> While MemAvailable shows 5G the kernel starts to drop cache from 4G down
>>> to 1G while the apache spawns some PHP processes. After that the PSI
>>> mem.some value rises and the kernel tries to reclaim memory but
>>> MemAvailable stays at 5G.
>>>
>>> Any ideas?
>>
>> Can you collect /proc/vmstat (every second or so) and post it while this
>> is the case please?
> 
> Yes sure.
> 
> But i don't know which event you mean exactly. Current situation is PSI
> / memory pressure is > 20 but:
> 
> This is the current status where MemAvailable show 5G but Cached is
> already dropped to 1G coming from 4G:
> 
> 
> meminfo:
> MemTotal:       16423116 kB
> MemFree:         5280736 kB
> MemAvailable:    5332752 kB
> Buffers:            2572 kB
> Cached:          1225112 kB
> SwapCached:            0 kB
> Active:          8934976 kB
> Inactive:        1026900 kB
> Active(anon):    8740396 kB
> Inactive(anon):   873448 kB
> Active(file):     194580 kB
> Inactive(file):   153452 kB
> Unevictable:       19900 kB
> Mlocked:           19900 kB
> SwapTotal:             0 kB
> SwapFree:              0 kB
> Dirty:              1980 kB
> Writeback:             0 kB
> AnonPages:       8423480 kB
> Mapped:           978212 kB
> Shmem:            875680 kB
> Slab:             839868 kB
> SReclaimable:     383396 kB
> SUnreclaim:       456472 kB
> KernelStack:       22576 kB
> PageTables:        49824 kB
> NFS_Unstable:          0 kB
> Bounce:                0 kB
> WritebackTmp:          0 kB
> CommitLimit:     8211556 kB
> Committed_AS:   32060624 kB
> VmallocTotal:   34359738367 kB
> VmallocUsed:           0 kB
> VmallocChunk:          0 kB
> Percpu:           118048 kB
> HardwareCorrupted:     0 kB
> AnonHugePages:   6406144 kB
> ShmemHugePages:        0 kB
> ShmemPmdMapped:        0 kB
> HugePages_Total:       0
> HugePages_Free:        0
> HugePages_Rsvd:        0
> HugePages_Surp:        0
> Hugepagesize:       2048 kB
> Hugetlb:               0 kB
> DirectMap4k:     2580336 kB
> DirectMap2M:    14196736 kB
> DirectMap1G:     2097152 kB
> 
> 
> vmstat shows:
> nr_free_pages 1320053
> nr_zone_inactive_anon 218362
> nr_zone_active_anon 2185108
> nr_zone_inactive_file 38363
> nr_zone_active_file 48645
> nr_zone_unevictable 4975
> nr_zone_write_pending 495
> nr_mlock 4975
> nr_page_table_pages 12553
> nr_kernel_stack 22576
> nr_bounce 0
> nr_zspages 0
> nr_free_cma 0
> numa_hit 13916119899
> numa_miss 0
> numa_foreign 0
> numa_interleave 15629
> numa_local 13916119899
> numa_other 0
> nr_inactive_anon 218362
> nr_active_anon 2185164
> nr_inactive_file 38363
> nr_active_file 48645
> nr_unevictable 4975
> nr_slab_reclaimable 95849
> nr_slab_unreclaimable 114118
> nr_isolated_anon 0
> nr_isolated_file 0
> workingset_refault 71365357
> workingset_activate 20281670
> workingset_restore 8995665
> workingset_nodereclaim 326085
> nr_anon_pages 2105903
> nr_mapped 244553
> nr_file_pages 306921
> nr_dirty 495
> nr_writeback 0
> nr_writeback_temp 0
> nr_shmem 218920
> nr_shmem_hugepages 0
> nr_shmem_pmdmapped 0
> nr_anon_transparent_hugepages 3128
> nr_unstable 0
> nr_vmscan_write 0
> nr_vmscan_immediate_reclaim 1833104
> nr_dirtied 386544087
> nr_written 259220036
> nr_dirty_threshold 265636
> nr_dirty_background_threshold 132656
> pgpgin 1817628997
> pgpgout 3730818029
> pswpin 0
> pswpout 0
> pgalloc_dma 0
> pgalloc_dma32 5790777997
> pgalloc_normal 20003662520
> pgalloc_movable 0
> allocstall_dma 0
> allocstall_dma32 0
> allocstall_normal 39
> allocstall_movable 1980089
> pgskip_dma 0
> pgskip_dma32 0
> pgskip_normal 0
> pgskip_movable 0
> pgfree 26637215947
> pgactivate 316722654
> pgdeactivate 261039211
> pglazyfree 0
> pgfault 17719356599
> pgmajfault 30985544
> pglazyfreed 0
> pgrefill 286826568
> pgsteal_kswapd 36740923
> pgsteal_direct 349291470
> pgscan_kswapd 36878966
> pgscan_direct 395327492
> pgscan_direct_throttle 0
> zone_reclaim_failed 0
> pginodesteal 49817087
> slabs_scanned 597956834
> kswapd_inodesteal 1412447
> kswapd_low_wmark_hit_quickly 39
> kswapd_high_wmark_hit_quickly 319
> pageoutrun 3585
> pgrotated 2873743
> drop_pagecache 0
> drop_slab 0
> oom_kill 0
> pgmigrate_success 839062285
> pgmigrate_fail 507313
> compact_migrate_scanned 9619077010
> compact_free_scanned 67985619651
> compact_isolated 1684537704
> compact_stall 205761
> compact_fail 182420
> compact_success 23341
> compact_daemon_wake 2
> compact_daemon_migrate_scanned 811
> compact_daemon_free_scanned 490241
> htlb_buddy_alloc_success 0
> htlb_buddy_alloc_fail 0
> unevictable_pgs_culled 1006521
> unevictable_pgs_scanned 0
> unevictable_pgs_rescued 997077
> unevictable_pgs_mlocked 1319203
> unevictable_pgs_munlocked 842471
> unevictable_pgs_cleared 470531
> unevictable_pgs_stranded 459613
> thp_fault_alloc 20263113
> thp_fault_fallback 3368635
> thp_collapse_alloc 226476
> thp_collapse_alloc_failed 17594
> thp_file_alloc 0
> thp_file_mapped 0
> thp_split_page 1159
> thp_split_page_failed 3927
> thp_deferred_split_page 20348941
> thp_split_pmd 53361
> thp_split_pud 0
> thp_zero_page_alloc 1
> thp_zero_page_alloc_failed 0
> thp_swpout 0
> thp_swpout_fallback 0
> balloon_inflate 0
> balloon_deflate 0
> balloon_migrate 0
> swap_ra 0
> swap_ra_hit 0
> 
> Greets,
> Stefan
>