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Groups > linux.debian.user > #199345 > unrolled thread

Swap priority in Debian

Started bySubhadip Ghosh <subhadip.sky@gmail.com>
First post2018-08-25 06:20 +0200
Last post2018-08-25 18:20 +0200
Articles 8 — 5 participants

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  Swap priority in Debian Subhadip Ghosh <subhadip.sky@gmail.com> - 2018-08-25 06:20 +0200
    Re: Swap priority in Debian Dekks Herton <dekkzz78@gmail.com> - 2018-08-25 09:50 +0200
      Re: Swap priority in Debian Subhadip Ghosh <subhadip.sky@gmail.com> - 2018-08-25 10:20 +0200
        Re: Swap priority in Debian Rick Thomas <rbthomas@pobox.com> - 2018-08-25 11:50 +0200
          Re: Re: Swap priority in Debian dekkzz78@gmail.com - 2018-08-25 13:10 +0200
    Re: Swap priority in Debian Reco <recoverym4n@gmail.com> - 2018-08-25 13:10 +0200
      Re: Swap priority in Debian Subhadip Ghosh <subhadip.sky@gmail.com> - 2018-08-25 14:40 +0200
        Re: Swap priority in Debian Reco <recoverym4n@gmail.com> - 2018-08-25 18:20 +0200

#199345 — Swap priority in Debian

FromSubhadip Ghosh <subhadip.sky@gmail.com>
Date2018-08-25 06:20 +0200
SubjectSwap priority in Debian
Message-ID<wqydj-Ux-1@gated-at.bofh.it>
Hi,

I am a Debian testing user. Recently I am experiencing freezing on my 
Debian system intermittently and during troubleshooting the same, I 
found out that the I have a swap partition with priority set to -2. But 
according to the below manpage:

https://manpages.debian.org/stretch/mount/swapon.8.en.html

swap priority should be between -1 and 32767. I have a swappiness value 
of 60 but I don't remember seeing the swap being used at all recently, 
the used swap is always 0%.

My question is, do you think that the -2 priority is stopping the swap 
partition from actually being used and because of that, the system is 
getting frozen when the memory usage is high?

Thanks,
Subhadip

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#199346

FromDekks Herton <dekkzz78@gmail.com>
Date2018-08-25 09:50 +0200
Message-ID<wqBux-2Hl-1@gated-at.bofh.it>
In reply to#199345
Subhadip Ghosh <subhadip.sky@gmail.com> writes:

> Hi,
>
> I am a Debian testing user. Recently I am experiencing freezing on my
> Debian system intermittently and during troubleshooting the same, I
> found out that the I have a swap partition with priority set to
> -2. But according to the below manpage:
>
> https://manpages.debian.org/stretch/mount/swapon.8.en.html
>
> swap priority should be between -1 and 32767. I have a swappiness
> value of 60 but I don't remember seeing the swap being used at all
> recently, the used swap is always 0%.

Whats swapon -s say? do you use zsawp or zram?

> My question is, do you think that the -2 priority is stopping the swap
> partition from actually being used and because of that, the system is
> getting frozen when the memory usage is high?

No, it's -2 on my stretch box with zswap enabled and it swaps as one
would expect.

-- 
Regards.........
 
PGP Fingerprint: 3DF8 311C 4740 B5BC 3867  72DF 1050 452F 9BCE BA00

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#199349

FromSubhadip Ghosh <subhadip.sky@gmail.com>
Date2018-08-25 10:20 +0200
Message-ID<wqBXA-35X-9@gated-at.bofh.it>
In reply to#199346
On Saturday 25 August 2018 01:17 PM, Dekks Herton wrote:
> Subhadip Ghosh <subhadip.sky@gmail.com> writes:
>
>> Hi,
>>
>> I am a Debian testing user. Recently I am experiencing freezing on my
>> Debian system intermittently and during troubleshooting the same, I
>> found out that the I have a swap partition with priority set to
>> -2. But according to the below manpage:
>>
>> https://manpages.debian.org/stretch/mount/swapon.8.en.html
>>
>> swap priority should be between -1 and 32767. I have a swappiness
>> value of 60 but I don't remember seeing the swap being used at all
>> recently, the used swap is always 0%.
> Whats swapon -s say? do you use zsawp or zram?
Filename                Type        Size    Used    Priority
/dev/sda5                                  partition    8203260 0    -2

I am using zswap.
>
>> My question is, do you think that the -2 priority is stopping the swap
>> partition from actually being used and because of that, the system is
>> getting frozen when the memory usage is high?
> No, it's -2 on my stretch box with zswap enabled and it swaps as one
> would expect.

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#199352

FromRick Thomas <rbthomas@pobox.com>
Date2018-08-25 11:50 +0200
Message-ID<wqDmF-3OD-3@gated-at.bofh.it>
In reply to#199349
On Aug 25, 2018, at 1:15 AM, Subhadip Ghosh <subhadip.sky@gmail.com> wrote:

> 
> On Saturday 25 August 2018 01:17 PM, Dekks Herton wrote:
>> Subhadip Ghosh <subhadip.sky@gmail.com> writes:
>> 
>>> Hi,
>>> 
>>> I am a Debian testing user. Recently I am experiencing freezing on my
>>> Debian system intermittently and during troubleshooting the same, I
>>> found out that the I have a swap partition with priority set to
>>> -2. But according to the below manpage:
>>> 
>>> https://manpages.debian.org/stretch/mount/swapon.8.en.html
>>> 
>>> swap priority should be between -1 and 32767. I have a swappiness
>>> value of 60 but I don't remember seeing the swap being used at all
>>> recently, the used swap is always 0%.
>> Whats swapon -s say? do you use zsawp or zram?
> Filename                Type        Size    Used    Priority
> /dev/sda5                                  partition    8203260 0    -2
> 
> I am using zswap.
>> 
>>> My question is, do you think that the -2 priority is stopping the swap
>>> partition from actually being used and because of that, the system is
>>> getting frozen when the memory usage is high?
>> No, it's -2 on my stretch box with zswap enabled and it swaps as one
>> would expect.
> 

My buster box says pretty much the same thing.  I’m not using zswap.

> Filename				Type		Size		Used	Priority
> /dev/dm-1                              	partition	10485756	0	-2

I don’t recall ever having seen it actually use any swap, but that may just be me not remembering something that didn’t seem important at the time.

Rick

PS:  I did manage, just now, to force it to swap a small, but non-zero, amount by opening lots of tabs in firefox.  So it will use a “-2” swap partition if it has to.
For what it’s worth, I noticed that firefox got kinda slow, but it didn’t freeze.

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#199356

Fromdekkzz78@gmail.com
Date2018-08-25 13:10 +0200
Message-ID<wqEC6-4Il-13@gated-at.bofh.it>
In reply to#199352

[Multipart message — attachments visible in raw view] — view raw

On 08/25, Rick Thomas wrote:
>
>On Aug 25, 2018, at 1:15 AM, Subhadip Ghosh <subhadip.sky@gmail.com> wrote:
>
>>
>> On Saturday 25 August 2018 01:17 PM, Dekks Herton wrote:
>>> Subhadip Ghosh <subhadip.sky@gmail.com> writes:
>>>
>>>> Hi,
>>>>
>>>> I am a Debian testing user. Recently I am experiencing freezing on my
>>>> Debian system intermittently and during troubleshooting the same, I
>>>> found out that the I have a swap partition with priority set to
>>>> -2. But according to the below manpage:
>>>>
>>>> https://manpages.debian.org/stretch/mount/swapon.8.en.html
>>>>
>>>> swap priority should be between -1 and 32767. I have a swappiness
>>>> value of 60 but I don't remember seeing the swap being used at all
>>>> recently, the used swap is always 0%.
>>> Whats swapon -s say? do you use zsawp or zram?
>> Filename                Type        Size    Used    Priority
>> /dev/sda5                                  partition    8203260 0    -2
>>
>> I am using zswap.
>>>
>>>> My question is, do you think that the -2 priority is stopping the swap
>>>> partition from actually being used and because of that, the system is
>>>> getting frozen when the memory usage is high?
>>> No, it's -2 on my stretch box with zswap enabled and it swaps as one
>>> would expect.
>>
>
>My buster box says pretty much the same thing.  I’m not using zswap.
>
>> Filename				Type		Size		Used	Priority
>> /dev/dm-1                              	partition	10485756	0	-2
>
>I don’t recall ever having seen it actually use any swap, but that may just be me not remembering something that didn’t seem important at the time.
>
>Rick
>
>PS:  I did manage, just now, to force it to swap a small, but non-zero, amount by opening lots of tabs in firefox.  So it will use a “-2” swap partition if it has to.
>For what it’s worth, I noticed that firefox got kinda slow, but it didn’t freeze.

I run stretch on a t60p with 2GB of RAM, so i know it swaps as normal. But both I and the OP use zswap which probably sets the prority to -2, FWIW swap space shows 300MB with the 
zswap space compressed to 110MB


-- 
regards.....

Dekks Herton

Thinkpad T61 2.0Ghz 2GB WSXGA+

Jabber IM: dekkzz78@jabber.hot-chilli.net

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#199357

FromReco <recoverym4n@gmail.com>
Date2018-08-25 13:10 +0200
Message-ID<wqEC6-4Il-15@gated-at.bofh.it>
In reply to#199345
	Hi.

On Sat, Aug 25, 2018 at 09:42:31AM +0530, Subhadip Ghosh wrote:
> Hi,
> 
> I am a Debian testing user. Recently I am experiencing freezing on my Debian
> system intermittently and during troubleshooting the same, I found out that
> the I have a swap partition with priority set to -2.

Same here with stable.


> But according to the below manpage:
> 
> https://manpages.debian.org/stretch/mount/swapon.8.en.html
> 
> swap priority should be between -1 and 32767.

So swapon(8) utility has this restriction. Note that the system call
itself - swapon(2) merely interprets swap priority as a signed integer,
so any priority number is actually possible (within integer limits of
course).


> I have a swappiness value of 60 but I don't remember seeing the swap
> being used at all recently, the used swap is always 0%.

A hint. They invented this wonderful thing called sysstat decades ago so
you don't have to remember your swap usage, along with other things
sysstat gathers.


> My question is, do you think that the -2 priority is stopping the swap
> partition from actually being used and because of that, the system is
> getting frozen when the memory usage is high?

No, it definitely does not work this way.
A swap priority only comes into play once you have multiple instances of
swaps. If you have a single swap partition/lv/file, a priority value is
meaningless.

A system freezes, on the other hand (did I mention sysstat?), could
indicate heavy swapping, barrier writes, kernel bugs (12309, anyone?),
oom killer invocations, overheating and many other things.
A good starting point would be kernel message log (aka
/var/log/kern.log) from the time of this freeze.

Reco

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#199361

FromSubhadip Ghosh <subhadip.sky@gmail.com>
Date2018-08-25 14:40 +0200
Message-ID<wqG1b-5pR-9@gated-at.bofh.it>
In reply to#199357

On Saturday 25 August 2018 04:29 PM, Reco wrote:
> 	Hi.
>
> On Sat, Aug 25, 2018 at 09:42:31AM +0530, Subhadip Ghosh wrote:
>> Hi,
>>
>> I am a Debian testing user. Recently I am experiencing freezing on my Debian
>> system intermittently and during troubleshooting the same, I found out that
>> the I have a swap partition with priority set to -2.
> Same here with stable.
>
>
>> But according to the below manpage:
>>
>> https://manpages.debian.org/stretch/mount/swapon.8.en.html
>>
>> swap priority should be between -1 and 32767.
> So swapon(8) utility has this restriction. Note that the system call
> itself - swapon(2) merely interprets swap priority as a signed integer,
> so any priority number is actually possible (within integer limits of
> course).
>
>
>> I have a swappiness value of 60 but I don't remember seeing the swap
>> being used at all recently, the used swap is always 0%.
> A hint. They invented this wonderful thing called sysstat decades ago so
> you don't have to remember your swap usage, along with other things
> sysstat gathers.
>
>
>> My question is, do you think that the -2 priority is stopping the swap
>> partition from actually being used and because of that, the system is
>> getting frozen when the memory usage is high?
> No, it definitely does not work this way.
> A swap priority only comes into play once you have multiple instances of
> swaps. If you have a single swap partition/lv/file, a priority value is
> meaningless.
>
> A system freezes, on the other hand (did I mention sysstat?), could
> indicate heavy swapping, barrier writes, kernel bugs (12309, anyone?),
> oom killer invocations, overheating and many other things.
> A good starting point would be kernel message log (aka
> /var/log/kern.log) from the time of this freeze.
Thanks for the suggestion. I checked the kern.log but did not find any 
suspicious log, in fact no entry from that exact time frame when the 
last freeze happened. Do you have any other suggestions to troubleshoot 
the freezes?

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#199364

FromReco <recoverym4n@gmail.com>
Date2018-08-25 18:20 +0200
Message-ID<wqJs5-7zr-11@gated-at.bofh.it>
In reply to#199361
	Hi.

On Sat, Aug 25, 2018 at 06:07:01PM +0530, Subhadip Ghosh wrote:
> 
> 
> On Saturday 25 August 2018 04:29 PM, Reco wrote:
> > 	Hi.
> > 
> > On Sat, Aug 25, 2018 at 09:42:31AM +0530, Subhadip Ghosh wrote:
> > > Hi,
> > > 
> > > I am a Debian testing user. Recently I am experiencing freezing on my Debian
> > > system intermittently and during troubleshooting the same, I found out that
> > > the I have a swap partition with priority set to -2.
> > Same here with stable.
> > 
> > 
> > > But according to the below manpage:
> > > 
> > > https://manpages.debian.org/stretch/mount/swapon.8.en.html
> > > 
> > > swap priority should be between -1 and 32767.
> > So swapon(8) utility has this restriction. Note that the system call
> > itself - swapon(2) merely interprets swap priority as a signed integer,
> > so any priority number is actually possible (within integer limits of
> > course).
> > 
> > 
> > > I have a swappiness value of 60 but I don't remember seeing the swap
> > > being used at all recently, the used swap is always 0%.
> > A hint. They invented this wonderful thing called sysstat decades ago so
> > you don't have to remember your swap usage, along with other things
> > sysstat gathers.
> > 
> > 
> > > My question is, do you think that the -2 priority is stopping the swap
> > > partition from actually being used and because of that, the system is
> > > getting frozen when the memory usage is high?
> > No, it definitely does not work this way.
> > A swap priority only comes into play once you have multiple instances of
> > swaps. If you have a single swap partition/lv/file, a priority value is
> > meaningless.
> > 
> > A system freezes, on the other hand (did I mention sysstat?), could
> > indicate heavy swapping, barrier writes, kernel bugs (12309, anyone?),
> > oom killer invocations, overheating and many other things.
> > A good starting point would be kernel message log (aka
> > /var/log/kern.log) from the time of this freeze.
> Thanks for the suggestion. I checked the kern.log but did not find any
> suspicious log, in fact no entry from that exact time frame when the last
> freeze happened. Do you have any other suggestions to troubleshoot the
> freezes?

"sar -r ALL -f 25" and "sar -S -f 25" would be the next logical step.
Note that "25" means current date (i.e. 25th of current month).

Should be preceeded by "apt install sysstat", of course.

Reco

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