On 17.03.2017 18:13, Michal Hocko wrote:
On Fri 17-03-17 17:37:48, Gerhard Wiesinger wrote:
[...]
Why does the kernel prefer to swapin/out and not use
a.) the free memory?
It will use all the free memory up to min watermark which is set up
based on min_free_kbytes.
Makes sense, how is /proc/sys/vm/min_free_kbytes default value calculated?
b.) the buffer/cache?
the memory reclaim is strongly biased towards page cache and we try to
avoid swapout as much as possible (see get_scan_count).
If I understand it correctly, swapping is preferred over dropping the
cache, right. Can this behaviour be changed to prefer dropping the cache
to some minimum amount?
Is this also configurable in a way?
(As far as I remember e.g. kernel 2.4 dropped the caches well).
There is ~100M memory available but kernel swaps all the time ...
Any ideas?
Kernel: 4.9.14-200.fc25.x86_64
top - 17:33:43 up 28 min, 3 users, load average: 3.58, 1.67, 0.89
Tasks: 145 total, 4 running, 141 sleeping, 0 stopped, 0 zombie
%Cpu(s): 19.1 us, 56.2 sy, 0.0 ni, 4.3 id, 13.4 wa, 2.0 hi, 0.3 si, 4.7
st
KiB Mem : 230076 total, 61508 free, 123472 used, 45096 buff/cache
procs -----------memory---------- ---swap-- -----io---- -system--
------cpu-----
r b swpd free buff cache si so bi bo in cs us sy id wa st
3 5 303916 60372 328 43864 27828 200 41420 236 6984 11138 11 47 6 23 14
I am really surprised to see any reclaim at all. 26% of free memory
doesn't sound as if we should do a reclaim at all. Do you have an
unusual configuration of /proc/sys/vm/min_free_kbytes ? Or is there
anything running inside a memory cgroup with a small limit?
nothing special set regarding /proc/sys/vm/min_free_kbytes (default
values), detailed config below. Regarding cgroups, none of I know. How
to check (I guess nothing is set because cg* commands are not available)?
cat /etc/sysctl.d/* | grep "^vm"
vm.dirty_background_ratio = 3
vm.dirty_ratio = 15
vm.overcommit_memory = 2
vm.overcommit_ratio = 80
vm.swappiness=10
find /proc/sys/vm -type f -exec echo {} \; -exec cat {} \;
/proc/sys/vm/admin_reserve_kbytes
8192
/proc/sys/vm/block_dump
0
/proc/sys/vm/compact_memory
cat: /proc/sys/vm/compact_memory: Permission denied
/proc/sys/vm/compact_unevictable_allowed
1
/proc/sys/vm/dirty_background_bytes
0
/proc/sys/vm/dirty_background_ratio
3
/proc/sys/vm/dirty_bytes
0
/proc/sys/vm/dirty_expire_centisecs
3000
/proc/sys/vm/dirty_ratio
15
/proc/sys/vm/dirty_writeback_centisecs
500
/proc/sys/vm/dirtytime_expire_seconds
43200
/proc/sys/vm/drop_caches
0
/proc/sys/vm/extfrag_threshold
500
/proc/sys/vm/hugepages_treat_as_movable
0
/proc/sys/vm/hugetlb_shm_group
0
/proc/sys/vm/laptop_mode
0
/proc/sys/vm/legacy_va_layout
0
/proc/sys/vm/lowmem_reserve_ratio
256 256 32 1
/proc/sys/vm/max_map_count
65530
/proc/sys/vm/memory_failure_early_kill
0
/proc/sys/vm/memory_failure_recovery
1
/proc/sys/vm/min_free_kbytes
45056
/proc/sys/vm/min_slab_ratio
5
/proc/sys/vm/min_unmapped_ratio
1
/proc/sys/vm/mmap_min_addr
65536
/proc/sys/vm/mmap_rnd_bits
28
/proc/sys/vm/mmap_rnd_compat_bits
8
/proc/sys/vm/nr_hugepages
0
/proc/sys/vm/nr_hugepages_mempolicy
0
/proc/sys/vm/nr_overcommit_hugepages
0
/proc/sys/vm/nr_pdflush_threads
0
/proc/sys/vm/numa_zonelist_order
default
/proc/sys/vm/oom_dump_tasks
1
/proc/sys/vm/oom_kill_allocating_task
0
/proc/sys/vm/overcommit_kbytes
0
/proc/sys/vm/overcommit_memory
2
/proc/sys/vm/overcommit_ratio
80
/proc/sys/vm/page-cluster
3
/proc/sys/vm/panic_on_oom
0
/proc/sys/vm/percpu_pagelist_fraction
0
/proc/sys/vm/stat_interval
1
/proc/sys/vm/stat_refresh
/proc/sys/vm/swappiness
10
/proc/sys/vm/user_reserve_kbytes
31036
/proc/sys/vm/vfs_cache_pressure
100
/proc/sys/vm/watermark_scale_factor
10
/proc/sys/vm/zone_reclaim_mode
0
Thnx.
Ciao,
Gerhard
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