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Old 04-05-2011, 07:15 PM
Daniel Gary
 
Default Bug#620993: closed by Ben Hutchings ( Bug#620993: general: Lenny 2.6.26-2 has noticably increased swap usage, tho not swap thrashing)

I have, but fixing monitoring to suit edge cases created from a recent
upgrade doesn't make the edge cases non-issues.


This is still an issue whether you want to hide it under nagios or not,
so I'd appreciate a little more assistance in finding the problem beyond
"fixing nagios".
If you go the doctors for a broken leg he doesn't just tell you "well
try not to walk on it".


The upgrades to 2.6.26-2 created anomalies, anomalies are bad.


On 4/5/2011 11:48 AM, Debian Bug Tracking System wrote:

This is an automatic notification regarding your Bug report
which was filed against the general package:

#620993: general: Lenny 2.6.26-2 has noticably increased swap usage, tho not swap thrashing

It has been closed by Ben Hutchings<ben@decadent.org.uk>.

Their explanation is attached below along with your original report.
If this explanation is unsatisfactory and you have not received a
better one in a separate message then please contact Ben Hutchings<ben@decadent.org.uk> by
replying to this email.







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Old 04-05-2011, 08:45 PM
Vincent Danjean
 
Default Bug#620993: closed by Ben Hutchings ( Bug#620993: general: Lenny 2.6.26-2 has noticably increased swap usage, tho not swap thrashing)

On 05/04/2011 21:15, Daniel Gary wrote:
> I have, but fixing monitoring to suit edge cases created from a recent upgrade
> doesn't make the edge cases non-issues.
>
> This is still an issue whether you want to hide it under nagios or not,

I do not understand the issue. You have some swap and you expect the
kernel *not* to use it ? *This* would be a bug. It is better that the
kernel swap out (parts of) processes it never uses and keep the RAM for
processes that need it.

Regards,
Vincent




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Old 04-05-2011, 09:17 PM
Daniel Gary
 
Default Bug#620993: closed by Ben Hutchings ( Bug#620993: general: Lenny 2.6.26-2 has noticably increased swap usage, tho not swap thrashing)

I'm not arguing that, I fully expect the kernel to use it to swap *if
needed*.
And if this was 20MB of swap, or maybe 100MB, ok, sure, the kernel might
be swapping old pages out, but 300MB+ swapping out in 2.6.26-2 where 0MB
swapped out in 2.6.26-1, and I can't find anything in the kernel.org or
debian kernel changelogs referencing a change along these lines doesn't
really scream "working as expected".
More annoying that the swap space never decreases unless swapoff/swapon
occurs


The closest thing I can find was a patch from Mel Gorman, but that
doesn't explain how the swap space is getting used in the first place,
or more how 2 otherwise identical machines have different amounts used,
0 and in the case I'm debugging ATM 312MB, Same make/model, same debian
lenny build, they're clones for all intents and purposes.


The only thing on these systems that has changed was 2.6.26-1 to
2.6.26-2, and swap wasn't being used to this extent, or staying used if
it was used, prior to 2.6.26-2.

Now it almost seems that once its used it doesn't get freed.

On 4/5/2011 1:45 PM, Vincent Danjean wrote:

On 05/04/2011 21:15, Daniel Gary wrote:

I have, but fixing monitoring to suit edge cases created from a recent upgrade
doesn't make the edge cases non-issues.

This is still an issue whether you want to hide it under nagios or not,

I do not understand the issue. You have some swap and you expect the
kernel *not* to use it ? *This* would be a bug. It is better that the
kernel swap out (parts of) processes it never uses and keep the RAM for
processes that need it.

Regards,
Vincent







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Old 04-05-2011, 09:47 PM
Russell Coker
 
Default Bug#620993: closed by Ben Hutchings ( Bug#620993: general: Lenny 2.6.26-2 has noticably increased swap usage, tho not swap thrashing)

On Wed, 6 Apr 2011, Daniel Gary <dgary1980@gmail.com> wrote:
> I'm not arguing that, I fully expect the kernel to use it to swap *if
> needed*.
> And if this was 20MB of swap, or maybe 100MB, ok, sure, the kernel might
> be swapping old pages out, but 300MB+ swapping out in 2.6.26-2 where 0MB

Using more memory for disk cache and less for storing rarely used pages sounds
like a performance optimisation.

Anyway I don't think that there's going to be much interest in performance-
tuning of Lenny kernels now that Squeeze is released.

If you want help in tuning Lenny then probably debian-user or your local LUG
mailing list would be the best option.

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Old 04-05-2011, 10:17 PM
Daniel Gary
 
Default Bug#620993: closed by Ben Hutchings ( Bug#620993: general: Lenny 2.6.26-2 has noticably increased swap usage, tho not swap thrashing)

On 4/5/2011 2:47 PM, Russell Coker wrote:

On Wed, 6 Apr 2011, Daniel Gary<dgary1980@gmail.com> wrote:

I'm not arguing that, I fully expect the kernel to use it to swap *if
needed*.
And if this was 20MB of swap, or maybe 100MB, ok, sure, the kernel might
be swapping old pages out, but 300MB+ swapping out in 2.6.26-2 where 0MB

Using more memory for disk cache and less for storing rarely used pages sounds
like a performance optimisation.
Fully agree, but I don't see anything in the changelog where that
optimization occurred. So while it sounds great in theory I can't back
it with the patches that went into 2.6.26-2 from 2.6.26-1.
Although it is what I've been telling the client is the likely case for
lack of a better answer and no loss in performance on the system.

Anyway I don't think that there's going to be much interest in performance-
tuning of Lenny kernels now that Squeeze is released.
Unfortunately an upgrade to Squeeze is a bit more involved than the
upgrade windows we have available, but I think may be the only option at
this point, but that's kind of like fixing a sparkplug that doesn't fire
by buying a new car, sure it'll probably do the job in the end, but that
doesn't really explain why the sparkplug doesn't fire.
But certainly a better reason to close the ticket than the previous one,
doesn't make it invalid, just makes it a wontfix.
I'd rather it be closed for someone being lazy than someone being
dismissive, a good sysadmin is a lazy sysadmin after all.



If you want help in tuning Lenny then probably debian-user or your local LUG
mailing list would be the best option.

Its not a tuning issue, its a change in a vacuum, more a freakish
annoyance than anything, it performs fine, we benchmarked before & after
and didn't notice any change either way other than these systems that
swap, well... swap.
The support tech in me says "screw it, it works", but the engineer in me
says "hmm, thats funny".




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