Re: [vserver] hashify and memory saving

From: Herbert Poetzl <>
Date: Fri 01 Jan 2016 - 21:25:06 GMT
Message-ID: <>

On Fri, Jan 01, 2016 at 09:37:52PM +0100, Tor Rune Skoglund wrote:
> Hello List,

Happy New Year!

> Having been a happy linux-vserver user for more than 10 years
> now, it was about time to test the hashify feature. The disk
> savings are obvious, and easily measured, but I have been
> trying a lot harder to measure any possible run-time memory
> savings.

> For the testing, I created a simple template LAMP guest, and
> a lot of hashified guests cloned from that one. I am unable
> to measure noticeably less memory usage when running multiple
> hashified guests compared to non-hashified ones using free and
> /proc/meminfo/'s MemAvailable entry.

> However, this could very well be to shortcomings in my own
> understanding how this should work or what to look for.

> What should I look for regarding possible memory savings?
> Anyone with any pointers?

You won't see any memory savings with dynamic memory allocations
and you won't get any benefits on read-write mappings either,
but you should be able to see a reduction for read only mappings
like they happen when using static binaries or read only mapped
shared libraries as well as read only memory mapped data files.

If I would devise a test to show the advantages, I would run a
binary which doesn't do many dynamic allocations but uses a lot
of code and/or libraries and run it as only process in each guest
with a few thousand guests in parallell, once with and without
unification in place.


> This is Gentoo, util-vserver 0.30.216_pre3120, kernel Linux amd64
> 3.18.7-vs2.3.7.4.

> BR, Tor Rune Skoglund
Received on Fri Jan 1 21:23:16 2016

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