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From Jered Floyd <je...@convivian.com>
Subject Re: TrafficServer using swap with almost 60GB still available
Date Fri, 22 Jul 2016 18:20:08 GMT
Kaivan, 

I believe you are misunderstanding how the Linux kernel uses swap. Swap is not just used to
avoid out-of-memory conditions, but also to free up cache memory by evicting infrequently
used blocks in memory. The behavior you are seeing is not unreasonable, but if you really
want to store everything in memory (which could reduce performance) you can adjust the "swappiness"
of your system. 

There are many good explanations of this online, here is one: 
http://askubuntu.com/questions/157793/why-is-swap-being-used-even-though-i-have-plenty-of-free-ram


--Jered 

----- On Jul 22, 2016, at 1:52 PM, Kaivan Sanghvi <kaivan.sanghvi@gmail.com> wrote:


> Hi,

> Recently we encountered that the traffic_server process was using about
> 7GB(total available 8GB) of swap space even when only half of the available
> physical memory(~68GB out of 128GB) was used up on the host. Can someone help
> us with why this might be happening and if we need to tweak any configurations
> for the same?

> Here is some more information:

> ATS : 5.1.2 using 24 6TB HDDs

> Ubuntu 14.04.4 LTS

> RAM Cache:
> traffic_line -r proxy.config.cache.ram_cache.size
> 21474836480

> cat /proc/18038/status

> Name: [ET_NET 0]
> State: S (sleeping)
> Tgid: 18038
> Ngid: 18082
> Pid: 18038
> PPid: 18017
> TracerPid: 0
> Uid: 65534 65534 65534 65534
> Gid: 65534 65534 65534 65534
> FDSize: 1024
> Groups: 0
> VmPeak: 62507948 kB
> VmSize: 60678648 kB
> VmLck: 0 kB
> VmPin: 0 kB
> VmHWM: 55435964 kB
> VmRSS: 50802704 kB
> VmData: 60601012 kB
> VmStk: 136 kB
> VmExe: 4188 kB
> VmLib: 8624 kB
> VmPTE: 105724 kB
> VmSwap: 7145508 kB
> Threads: 247
> SigQ: 0/1027883
> SigPnd: 0000000000000000
> ShdPnd: 0000000000000000
> SigBlk: 0000000000000000
> SigIgn: 0000000000381000
> SigCgt: 0000000180004e4f
> CapInh: 0000000000000000
> CapPrm: 0000000000005402
> CapEff: 0000000000005400
> CapBnd: 0000001fffffffff
> Seccomp: 0
> Cpus_allowed: ffffffff
> Cpus_allowed_list: 0-31
> Mems_allowed: 00000000,00000003
> Mems_allowed_list: 0-1
> voluntary_ctxt_switches: 444748631
> nonvoluntary_ctxt_switches: 627214

> HTOP output showing swap usage and almost half of physical memory still
> available :

> cat /proc/meminfo

> MemTotal: 131590680 kB
> MemFree: 60468340 kB
> Buffers: 602848 kB
> Cached: 8235876 kB
> SwapCached: 2261820 kB
> Active: 60177604 kB
> Inactive: 8754340 kB
> Active(anon): 52968336 kB
> Inactive(anon): 7126492 kB
> Active(file): 7209268 kB
> Inactive(file): 1627848 kB
> Unevictable: 0 kB
> Mlocked: 0 kB
> SwapTotal: 8000508 kB
> SwapFree: 4000400 kB
> Dirty: 796 kB
> Writeback: 0 kB
> AnonPages: 59005956 kB
> Mapped: 56164 kB
> Shmem: 1600 kB
> Slab: 1066076 kB
> SReclaimable: 835516 kB
> SUnreclaim: 230560 kB
> KernelStack: 8840 kB
> PageTables: 144336 kB
> NFS_Unstable: 0 kB
> Bounce: 0 kB
> WritebackTmp: 0 kB
> CommitLimit: 73795848 kB
> Committed_AS: 64516392 kB
> VmallocTotal: 34359738367 kB
> VmallocUsed: 484776 kB
> VmallocChunk: 34291077428 kB
> HardwareCorrupted: 0 kB
> AnonHugePages: 39610368 kB
> HugePages_Total: 0
> HugePages_Free: 0
> HugePages_Rsvd: 0
> HugePages_Surp: 0
> Hugepagesize: 2048 kB
> DirectMap4k: 113280 kB
> DirectMap2M: 3631104 kB
> DirectMap1G: 132120576 kB

> cat /proc/sys/vm/max_map_count
> 65530

> Thanks,
> Kaivan.

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