AW: [cod] Multiple Servers on one box and PB

Mark J. DeFilippis defilm at acm.org
Sat May 15 15:03:06 EDT 2004


Yes, you are correct. Using separate executables, with different INODE 
numbers, Linux has no idea that the code pages are the same. The benefit I 
enumerated will NOT be seen.  The only benefit will indeed be in the shared 
library routines, and this can be very limited as you point out. The 
libraries are "re-entrant", so this benefit will be seen even if separate 
executables are invoked.

I should have mentioned that the invocation of the executable MUST be the 
same INODE to obtain the maximum memory advantage to which I 
referred.  (Every file in Linux is known by it's INODE number, not it's 
name). So if it is a different INODE, Linux has no idea that the code pages 
are the same.

One simple way to so this is by making a Symbolic link. Do NOT copy them, but
instead, for each file in the original file structure, make a symbolic link.

Instead of  cp $home/cod/cod_linuxex  $home/cod2/

perform a symbolic link:

ln -s $home/cod/cod_linuxex $home/cod2/cod_linuxex

If you now check the two files, you will see one points at the other.

ls -li $home/cod/cod_linuxex

and

ls -li $home/cod2/cod_linuxex

The INODE number will be the first value listed. They should be the 
same.  This means the
invocation from $home/cod and $home/cod2 will use the SAME executable.

****Note, you can not symbolic link across filesystems.  If you do, Linux 
will make
a copy.  So if the /usr directory is a different filesystem than the 
/gaming directory,
Linux will make a copy.  Make sure for all servers you plan to execute, 
they are on the
same filesystem, and they will all be one executable. (Note that the 
symbolic link only
takes a few blocks of disk space)... yea... just another side benefit...

Have fun.

Thank you Joe for making this very critical observation!

MD



At 02:07 PM 5/15/2004, Joe Brown wrote:
>Hi Mark,
>
>Thanks for sharing your knowledge and taking your time to explain these 
>technical details in a language I can understand.
>One of the reasons this thread started: I mentioned to a colleague, I 
>prefer to run servers from one install of a game server, to allow the OS 
>to make use of shared libraries.  Althought I think the advantages are 
>somewhat minor, there are still system performance issues that will be 
>realized.
>
>For a server instance, some ppl have a tendency to make a copy of all the 
>game server files in seperate home directories for each server 
>instance.  Because these files are a copies, not linked or the same 
>physical file image, I'm working on the assumption the OS has no means to 
>identify that the same executable is being run mutiple times, because it's 
>executing from seperate copies.
>
>There are a couple of issues in system performance, I don't care for, when 
>this happens.
>1st, any file caching benifits are out the window.  I don't believe system 
>performace will take a very noticable hit on this, it's effects are fairly 
>well hidden and hard to observe.  But it is there.
>
>2nd, I suspect more memory will be consumed by running game servers from 
>seperate copies, because shared libraries won't be shared as they could 
>be.  <- I'm in the dark about the accuracy of this statement tho.
>
>I'm a performance junkie.  If I can make things perform better, I'll go 
>the distance to make it so.  But when a guy tells me he can't see a 
>difference in one method vs. another and I cannot refute that with 
>tangible details, I find myself in bit of a quandery.
>
>I would appreciate if you could elaborate on these issues, my technical 
>knowledge is far less intimate with the internals of the kernel.
>
>
>Thanks Again,
>
>-Joe
>

-------------------------------------------------------------------------------
Mark J. DeFilippis                    defilm at acm.org
                                       defilm at ieee.org


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