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Excessive page-outs, even after memory upgrade

 
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Andrew Scott_3
Regular Advisor

Excessive page-outs, even after memory upgrade

We have an rx4640 with 4 single-core Itaniums running some Oracle standby instances, and are having some serious performance issues with it.

Originally, we were running with 12GB of RAM. We were seeing massive paging activity and were several gigabytes into swap.

We have since increased the system RAM to 32GB. We are no longer into physical disk-based swap, but swapinfo is still showing 1000-1500 page-outs a second, and total page-faults are running in the 8-10 thousand range.

Since we are using 0 blocks of physical swap, I'm guessing the page-outs are going to pseudo-swap.

Glance is showing 30.4GB of pseudo-swap available, and 7.2GB of it used on the system.

How can I get this sucker to stop paging out so much? We're only 24% utilized on physical memory at the current time. Our shmmax is 4GB and I have the buffer cache constrained to 10$ of available memory. What other kernel parameters do we need to check?

Also, I know that page-in counts include code loaded from disk to be run from memory. Do page-out counts include data written to disk by programs? The manpage for vmstat isn't clear on that.

Thanks!
Andrew
18 REPLIES 18
Steven E. Protter
Exalted Contributor

Re: Excessive page-outs, even after memory upgrade

Shalom Andrew,

Lets take a look at application usage.

Check the oracle SGA's and such. Trim your buffer pool if possible, to free up memory.

Lets take a look at glance and see what processes are using how much memory. Lets identify the porcess actually using the memory (top can do this) and take action on that basis.

Remember, an application will reserve swap even if it never uses it.

SEP
Steven E Protter
Owner of ISN Corporation
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Andrew Scott_3
Regular Advisor

Re: Excessive page-outs, even after memory upgrade

Here's my glance process list output. The three stdbypr01 processes are my biggest offenders. An occasional gzip will run out of a cron job and cripple the system, but I haven't been able to capture that running in glance yet.

Dennis Handly
Acclaimed Contributor

Re: Excessive page-outs, even after memory upgrade

>swapinfo is still showing 1000-1500 page-outs a second, and total page-faults are running in the 8-10 thousand range.

swapinfo(1m) doesn't show that. (Please provide the "swapinfo -tam" and vmstat output.)
Did you mean vmstat(1)?

>Since we are using 0 blocks of physical swap, I'm guessing the page-outs are going to pseudo-swap.

I'm not sure how useful this is for the kernel to do this?

>Do page-out counts include data written to disk by programs?

It depends on whether you have mapped files.
I'm not sure if it applies to the file cache on 11.31?
Andrew Scott_3
Regular Advisor

Re: Excessive page-outs, even after memory upgrade

Attached is a process detail on one of our big Oracle processes.

>swapinfo(1m) doesn't show that. (Please provide the "swapinfo -tam" and vmstat output.)
>Did you mean vmstat(1)?

Yes, I did. Sorry.

>>Since we are using 0 blocks of physical swap, I'm guessing the page-outs are going to pseudo-swap.

>I'm not sure how useful this is for the kernel to do this?

It's not useful at all, but that doesn't stop the system from doing it. The way I understand pseudo swap is the VM requires there to be a page of swap for every page of memory allocated, and they came up with pseudo swap so that they could create the pages in memory instead of on disk when available RAM allowed it.

And perhaps my page-outs are simply page creations in pseudo swap and not actual page outs? I don't know, and I don't know how to tell.

>>Do page-out counts include data written to disk by programs?

>It depends on whether you have mapped files.
I'm not sure if it applies to the file cache on 11.31?

I don't know, either.
Andrew Scott_3
Regular Advisor

Re: Excessive page-outs, even after memory upgrade

Ooops, forgot the attachment
Dennis Handly
Acclaimed Contributor

Re: Excessive page-outs, even after memory upgrade

>It's not useful at all, but that doesn't stop the system from doing it.

I would assume it isn't doing it and there is some other cause.

>they came up with pseudo swap so that they could create the pages in memory instead of on disk when available RAM allowed it.

Yes. The page is its own swap area.

>perhaps my page-outs are simply page creations in pseudo swap and not actual page outs?

I would assume they would suppress these as confusing. Or put them under some other statistic.

>I don't know, either.

Are you using 11.31? Do you have all the latest VM patches?

Your attachment says it is waiting for I/O.
It has FS Reads/Writes. No VM Reads/Writes. Some System Writes.
Andrew Scott_3
Regular Advisor

Re: Excessive page-outs, even after memory upgrade

Yes, I'm on 11.31, and I'm patched up to March 2009.

As for the process being in IO Wait, yes. Everything is almost always in IO wait on this system. That's the core problem I'm trying to solve: why is everything in IO Wait all the time?

The system has two 2GB fiber channel cards and has its own EVA 8400 with 91 spindles (all in one disk group). We have CA eHealth watching the fabric and the server, and its telling me the fiber channel cards are under 10% utilized, but my disk is grinding away at 30-70%. My CPU loads are hovering around 70%, mostly due to IO wait.

I ran evaperf against the EVA and processed the results through TLVIZ and found a few nasty spikes, but on average we're not hurting for storage speed and my controller utilization is really low. My write latencies spike to 9 or 10ms during a few really heavy spots where multiple instances are applying transaction logs at the same time, but on average are hovering around 4ms.

I have a bottleneck somewhere, I just can't find it. These excessive page-outs seemed like a good place to start looking.

I checked with the DBAs, and the total SGA allocated for all of the database instances was just 4GB, as they had not yet increased them from before the memory upgrade.

Would having the SGA size set too low cause excessive paging?

Oh, and this system is ~84% WRITE on its data disks. So consider that in any parameter change recommendations.
Emil Velez
Honored Contributor

Re: Excessive page-outs, even after memory upgrade

If you are only using 24% of physical memory you do not have any pageouts.

You might have pageins which are ok but not pageouts. You may be misunderstanding the output of the vmstat memory report. You will not get pageouts unless you are low on memory and all of it is used.

You might want to increase the amount of filecache_max

How is your oracle databases setup. JFS filesystem, RAC with CFS or Raw Lvs ?
Dennis Handly
Acclaimed Contributor

Re: Excessive page-outs, even after memory upgrade

>why is everything in IO Wait all the time?
>My CPU loads are hovering around 70%, mostly due to IO wait.

These are separate/opposite. You could be up to 30% IO wait.

>I have a bottleneck somewhere, I just can't find it. These excessive page-outs seemed like a good place to start looking.

How do you know the page-outs are for these processes?

>Would having the SGA size set too low cause excessive paging?

Or lots of I/O.