* Swap causing huge latency on disk IO operations
@ 2017-09-09 18:36 Sudharsan Vijayaraghavan
2017-09-10 5:02 ` Greg KH
0 siblings, 1 reply; 6+ messages in thread
From: Sudharsan Vijayaraghavan @ 2017-09-09 18:36 UTC (permalink / raw)
To: kernelnewbies
Hi All,
We are running a pretty (rather a very old kernel) 2.6.32. Nevertheless we
do see huge latency on disk IO once system starts using swap.
Tweaking of various swap related variables under /proc/sys/vm did not make
a big difference.
The idea is we are having big memory requirement, hence using swap is
expected. Unexpected thing is that this is causing very high latency.
The precise latency happens as follows
swap_readpage () invokes lock_page() and then the process(thread) of
interest gets scheduled out through io_schedule(), it does not run again
for several seconds.
This occurs due to the fact another thread is writing to disk using ext3
functions, wherein it
took lock_page() and spends lot of time to write data to disk before
finally invoking unlock_page().
top shows huge iowaits (nr_iowait).
Is it expected design behavior that Linux performs bad with swap
particularly for disk operations?
Tweaking elevator algorithm, io size, block size also did not help.
Now we are changing ext3 mounts from data=ordered to data=writeback to see
if it helps to reduce disk latency when we run into swap usage.
We use RAID along with LVM. We are also experimenting by removing LVM to
see if improves the behaviour.
Any inputs will be immense help
Thanks,
Sudharsan
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* Swap causing huge latency on disk IO operations
2017-09-09 18:36 Swap causing huge latency on disk IO operations Sudharsan Vijayaraghavan
@ 2017-09-10 5:02 ` Greg KH
2017-09-10 5:56 ` Sudharsan Vijayaraghavan
2017-09-10 6:02 ` Ruben Safir
0 siblings, 2 replies; 6+ messages in thread
From: Greg KH @ 2017-09-10 5:02 UTC (permalink / raw)
To: kernelnewbies
On Sun, Sep 10, 2017 at 12:06:36AM +0530, Sudharsan Vijayaraghavan wrote:
> Hi All,
>
> We are running a pretty (rather a very old kernel) 2.6.32. Nevertheless we do
> see huge latency on disk IO once system starts using swap.
That's your problem, 2.6.32 is _very_ old and obsolete. No one in the
community can help you out with that release anymore, sorry.
Please go get support from the company that is forcing you to stay at
such an old kernel version, as you are already paying them for that
support.
I strongly recommend you use a more modern kernel release, you will find
that things should be _much_ better...
good luck!
greg k-h
^ permalink raw reply [flat|nested] 6+ messages in thread
* Swap causing huge latency on disk IO operations
2017-09-10 5:02 ` Greg KH
@ 2017-09-10 5:56 ` Sudharsan Vijayaraghavan
2017-09-10 6:02 ` Greg KH
2017-09-10 6:06 ` Ruben Safir
2017-09-10 6:02 ` Ruben Safir
1 sibling, 2 replies; 6+ messages in thread
From: Sudharsan Vijayaraghavan @ 2017-09-10 5:56 UTC (permalink / raw)
To: kernelnewbies
Hi Greg,
My general question is that has the community seen "swap latency issues
with disk IO" in general. Further can we assume that later kernels (like
4.4) does not exhibit such a behavior.
Thanks,
Sudharsan
On Sun, Sep 10, 2017 at 10:32 AM, Greg KH <greg@kroah.com> wrote:
> On Sun, Sep 10, 2017 at 12:06:36AM +0530, Sudharsan Vijayaraghavan wrote:
> > Hi All,
> >
> > We are running a pretty (rather a very old kernel) 2.6.32. Nevertheless
> we do
> > see huge latency on disk IO once system starts using swap.
>
> That's your problem, 2.6.32 is _very_ old and obsolete. No one in the
> community can help you out with that release anymore, sorry.
>
> Please go get support from the company that is forcing you to stay at
> such an old kernel version, as you are already paying them for that
> support.
>
> I strongly recommend you use a more modern kernel release, you will find
> that things should be _much_ better...
>
> good luck!
>
> greg k-h
>
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* Swap causing huge latency on disk IO operations
2017-09-10 5:56 ` Sudharsan Vijayaraghavan
@ 2017-09-10 6:02 ` Greg KH
2017-09-10 6:06 ` Ruben Safir
1 sibling, 0 replies; 6+ messages in thread
From: Greg KH @ 2017-09-10 6:02 UTC (permalink / raw)
To: kernelnewbies
On Sun, Sep 10, 2017 at 11:26:14AM +0530, Sudharsan Vijayaraghavan wrote:
> Hi Greg,
>
> My general question is that has the community seen "swap latency issues with
> disk IO" in general. Further can we assume that later kernels (like 4.4) does
> not exhibit such a behavior.
"later" kernels are hundreds of thousands of changes newer than the
kernel you are using, so really, the responsibility is for you to try it
out on your workload to see if it works better or not (and if not, then
let the developers know, after you have tried 4.13). There is nothing
we can do to go back in time and change an obsolete, old, kernel version
:)
good luck!
greg k-h
^ permalink raw reply [flat|nested] 6+ messages in thread
* Swap causing huge latency on disk IO operations
2017-09-10 5:56 ` Sudharsan Vijayaraghavan
2017-09-10 6:02 ` Greg KH
@ 2017-09-10 6:06 ` Ruben Safir
1 sibling, 0 replies; 6+ messages in thread
From: Ruben Safir @ 2017-09-10 6:06 UTC (permalink / raw)
To: kernelnewbies
On 09/10/2017 01:56 AM, Sudharsan Vijayaraghavan wrote:
>
> My general question is that has the community seen "swap latency issues
> with disk IO" in general. Further can we assume that later kernels (like
> 4.4) does not exhibit such a behavior.
the problems with swap is not limited to any specific OS, and in fact,
Linux does it fairly well.
You're dealing with a Hardware device which is suseptable to numerous
troubles,
--
So many immigrant groups have swept through our town
that Brooklyn, like Atlantis, reaches mythological
proportions in the mind of the world - RI Safir 1998
http://www.mrbrklyn.com
DRM is THEFT - We are the STAKEHOLDERS - RI Safir 2002
http://www.nylxs.com - Leadership Development in Free Software
http://www2.mrbrklyn.com/resources - Unpublished Archive
http://www.coinhangout.com - coins!
http://www.brooklyn-living.com
Being so tracked is for FARM ANIMALS and and extermination camps,
but incompatible with living as a free human being. -RI Safir 2013
^ permalink raw reply [flat|nested] 6+ messages in thread
* Swap causing huge latency on disk IO operations
2017-09-10 5:02 ` Greg KH
2017-09-10 5:56 ` Sudharsan Vijayaraghavan
@ 2017-09-10 6:02 ` Ruben Safir
1 sibling, 0 replies; 6+ messages in thread
From: Ruben Safir @ 2017-09-10 6:02 UTC (permalink / raw)
To: kernelnewbies
On 09/10/2017 01:02 AM, Greg KH wrote:
> That's your problem, 2.6.32 is _very_ old and obsolete. No one in the
> community can help you out with that release anymore, sorry.
that is true, but swapping at times is still a huge problem. I tend to
just turn it off.
--
So many immigrant groups have swept through our town
that Brooklyn, like Atlantis, reaches mythological
proportions in the mind of the world - RI Safir 1998
http://www.mrbrklyn.com
DRM is THEFT - We are the STAKEHOLDERS - RI Safir 2002
http://www.nylxs.com - Leadership Development in Free Software
http://www2.mrbrklyn.com/resources - Unpublished Archive
http://www.coinhangout.com - coins!
http://www.brooklyn-living.com
Being so tracked is for FARM ANIMALS and and extermination camps,
but incompatible with living as a free human being. -RI Safir 2013
^ permalink raw reply [flat|nested] 6+ messages in thread
end of thread, other threads:[~2017-09-10 6:06 UTC | newest]
Thread overview: 6+ messages (download: mbox.gz follow: Atom feed
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2017-09-09 18:36 Swap causing huge latency on disk IO operations Sudharsan Vijayaraghavan
2017-09-10 5:02 ` Greg KH
2017-09-10 5:56 ` Sudharsan Vijayaraghavan
2017-09-10 6:02 ` Greg KH
2017-09-10 6:06 ` Ruben Safir
2017-09-10 6:02 ` Ruben Safir
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