FileCache effects on memory in 11.31

[Olivier Masse]

With 11.23 and earlier, I used to set dbc_max_pct very conservatively. Now with 11.31, I currently don't change filecache_max at all and use the defaults.

However, some savvy users and developpers are noticing in glance that memory usage is almost at 100%, and they're seeing pageins/pageouts too. This is especially noticeable on servers that don't have much memory (8GB or less).

I simply tell them to substract the value of "FileCache" to have an approximation of what usable memory is left, and that the pageouts are probably fake and do not mean there is memory pressure... but is spreading this info actually true? Not sure. Is there any whitepaper somewhere that could help me understand what's going on so that I could give them a proper explanation?

I prefer keeping default setting whenever possible but many are currently misinterpreting the free memory report in glance (me included) and I can't blame them. Should I just reduce filecache_max and be done with it?

Olivier

[Patrick Wallek]

What does 'swapinfo -tam' show? What is the rate of pageouts?

If you are actually using device swap space, then there may well be memory pressure. If the pageout rate is into double or triple digits, then that can indicate memory pressure as well.

[Olivier Masse]

swapinfo -tam output attached

[Olivier Masse]

I'm also attaching a screenshot of what I'm seeing in glance's memory report. The paging rate is high but didn't stay like that for long.

Thanks

[James R. Ferguson · Accepted solution]

Hi Olivier:

Don Morris has commented several times on questions of memory usage and the 11.31 file cache. I would read is comments in threads like:

http://forums.itrc.hp.com/service/forums/questionanswer.do?threadId=1240472

http://forums.itrc.hp.com/service/forums/questionanswer.do?threadId=1340096

http://forums.itrc.hp.com/service/forums/questionanswer.do?threadId=1337908

http://forums.itrc.hp.com/service/forums/questionanswer.do?threadId=1397119

There is also a discussion of the filecache in the classic Performance Cookbook whitepaper:

http://h21007.www2.hp.com/portal/download/files/unprot/devresource/Docs/TechPapers/UXPerfCookBook.pdf

And, then as always recommended, review:

http://docs.hp.com/en/B2355-60130/filecache_max.5.html

Regards!

...JRF...

[Patrick Wallek]

You have or have had some memory pressure in the past. You are using 9% device swap so some memory pages have been pushed out to swap.

I would look into reducing memory consumption somehow. If it is via reducing FileCache, so be it.

[Olivier Masse]

Reading Don's posts now.

Thanks !!

[Duncan Edmonstone]

Olivier,

There's a knowledge on demand webcast on the UFC here which might also be helpful:

http://h71028.www7.hp.com/enterprise/w1/en/os/hpux11i-kod-unified-file-cache.html

I'm pretty sure there also used to be a detailed whitepaper on the UFC too - but it seems to have been removed - I'm out of the office right now, but will try and find out whether the removal was deliberate or an error some time next week...

HTH

Duncan