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Date:      Fri, 10 Jun 2022 21:32:10 -0700
From:      Mark Millard <marklmi@yahoo.com>
To:        FreeBSD Hackers <freebsd-hackers@freebsd.org>
Cc:        Daniel Ebdrup Jensen <debdrup@freebsd.org>, David Cross <david@crossfamilyweb.com>, Robert Clausecker <fuz@fuz.su>
Subject:   Re: What can I learn about data that is staying paged out? (There is a more specific poudriere bulk related context given.)
Message-ID:  <6EA27152-3355-4356-B246-A083F31452F2@yahoo.com>
In-Reply-To: <573B8B0C-5209-459D-98AD-EE92DDA4DF83@yahoo.com>
References:  <C337A09C-D546-46FC-A166-DBB3237D1AFC@yahoo.com> <A9C9AC24-62EC-43C1-B713-F2012CD1FD5B@yahoo.com> <573B8B0C-5209-459D-98AD-EE92DDA4DF83@yahoo.com>

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On 2022-Jun-10, at 21:27, Mark Millard <marklmi@yahoo.com> wrote:

> On 2022-Jun-5, at 15:04, Mark Millard <marklmi@yahoo.com> wrote:
>=20
>> On 2022-Jun-5, at 12:42, Mark Millard <marklmi@yahoo.com> wrote:
>>=20
>>> I have a poudriere bulk -a -c going on a 8 Gibyte
>>> aarch64 system. top has been showing an occasionally
>>> increasing swap usage but never any sizable decreases.
>>> Over 5800 ports have built so far. The context is UFS
>>> only. The system is running a non-debug build of main.
>>>=20
>>> Part of the context is ( in /etc/sysctl.conf ):
>>>=20
>>> vm.swap_enabled=3D0
>>> vm.swap_idle_enabled=3D0
>>>=20
>>> Also ( in /usr/local/etc/poudriere.conf ):
>>>=20
>>> USE_TMPFS=3D"data"
>>>=20
>>> poudriere's TMPFS reports normally total under 128
>>> KiBytes across the 4 builders.
>>>=20
>>> For reference, example figures . . .
>>>=20
>>> A top variant shows:
>>>=20
>>> Swap: 30720Mi Total, 306816Ki Used
>>>=20
>>> vmstat -s shows:
>>>=20
>>>  78152 swap pager pages paged out
>>>=20
>>> Note: (78152*4096)/1024 =3D=3D 312608Ki
>>>=20
>>> So nearly all of the "swap pager pages paged out"
>>> pages are still sitting out in the used swap/paging
>>> space. Thus, the usage is not held by user processes
>>> or is held via very long running processes or is
>>> not directly tied to user processes --or some mix.
>>>=20
>>> The variant of top reports never having observed
>>> more than: 6658Mi MaxObs(Act+Wir+Lndry).
>>> ("MaxObs" is short for "Maximum Observed".)
>>> Such high usage is for a bounded time, long past
>>> at this point. (Until some combination of port
>>> builds ends up active that uses such.)
>>>=20
>>> So I'm curious:
>>>=20
>>> What can I learn about the data that is staying
>>> paged out (and is gradually growing)? How can I
>>> learn it?
>>>=20
>>>=20
>>> Other notes:
>>>=20
>>> The poudriere jail being built is:
>>>=20
>>> # poudriere jail -jmain-CA7-bulk_a -i
>>> Jail name:         main-CA7-bulk_a
>>> Jail version:      14.0-CURRENT
>>> Jail arch:         arm.armv7
>>> Jail method:       null
>>> Jail mount:        /usr/obj/DESTDIRs/main-CA7-poud-bulk_a
>>> Jail fs:          =20
>>> Jail updated:      2022-05-23 02:21:24
>>> Jail pkgbase:      disabled
>>>=20
>>> (Just in case the armv7 jail usage or the null method
>>> or such is important to the issue.)
>>=20
>> Hmm. systat -swap reports a toal for the Devices/Paths Used
>> that is somewhat less than the total for what reports for the
>> Pid . . . Total figures (not the Pid Swap figures!):
>>=20
>> # systat -swap
>>                   /0   /1   /2   /3   /4   /5   /6   /7   /8   /9   =
/10
>>    Load Average   ||||||||  =20
>>=20
>> Device/Path       Size  Used |0%  /10  /20  /30  /40  / 60\  70\  80\ =
 90\ 100|
>> gpt/CA72USBswp14   14G  150M
>> gpt/CA72USBswp16   16G  150M
>> Total              30G  300M
>>=20
>> Pid    Username   Command     Swap/Total Per-Process    Per-System
>> 1453 root       nfsd         1M /  15M  9%              0%
>> 1451 root       mountd       1M /  15M  7%              0%
>> 1481 root       sshd       912K /  20M  4%              0%
>> 1406 root       ntpd       740K /  27M  2%              0%
>> 1513 root       login      724K /  14M  5%              0%
>> 1514 root       sh         656K /  13M  4%              0%
>>  342 _dhcp      dhclient   516K /  13M  3%              0%
>> 1363 root       rpcbind    448K /  13M  3%              0%
>> 1454 root       nfsd       400K /  12M  3%              0%
>>  341 root       dhclient   380K /  13M  2%              0%
>> 1341 root       syslogd    324K /  12M  2%              0%
>> 1505 root       getty      292K /  12M  2%              0%
>> 1510 root       getty      292K /  12M  2%              0%
>> 1511 root       getty      292K /  12M  2%              0%
>> 1512 root       getty      292K /  12M  2%              0%
>> 1509 root       getty      292K /  12M  2%              0%
>> 1508 root       getty      292K /  12M  2%              0%
>> 1507 root       getty      292K /  12M  2%              0%
>> 1506 root       getty      288K /  12M  2%              0%
>> 1135 root       devd       272K /  11M  2%              0%
>>  338 root       dhclient   264K /  13M  2%              0%
>>    1 root       init       244K /  11M  2%              0%
>> 1486 root       cron       188K /  13M  1%              0%
>>=20
>> I'm, Still looking for a clear indication of what
>> most of the 300 MiBytes or so of swap/paging space
>> is in use for.
>=20
> I finally gave up and checked if a swapoff would
> actually bring in all the pages from swap space
> that were needed (if any) and then un-configure
> the swap space. It did. (The bulk -a was still
> ongoing. It was not doing memory-hog builder
> activity at the time.)
>=20
> So such an activity may be a workaround for long
> running things like bulk -a to avoid a swap space
> accumulation that seems to be happening.
>=20
> I do not know how much was brought in to RAM vs.
> simply deallocated from swap space (pages not
> changed and still in RAM). If I do such a test
> again, it would be good to figure out how to
> monitor what the swapoff does for bringing in
> pages vs. just discarding them --if possible.
>=20
> After a while 12136Ki Used showed up after the
> swapon that reconfigured the swap space, which is
> about the size of the increments that I'd observed
> for its sustained increases.
>=20

An interesting point for "systat -swap" now:

                    /0   /1   /2   /3   /4   /5   /6   /7   /8   /9   =
/10
     Load Average   |||||||||||||||||||||||||||||

Device/Path       Size  Used |0%  /10  /20  /30  /40  / 60\  70\  80\  =
90\ 100|
gpt/CA72USBswp14   14G 6108K
gpt/CA72USBswp16   16G 6028K
Total              30G   12M

Pid    Username   Command     Swap/Total Per-Process    Per-System


No process is listed as using swap but the 12M
shows as used! That should be a hint, not that
it is directly useful for me figuring out what
the usage is from/for.


=3D=3D=3D
Mark Millard
marklmi at yahoo.com




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