Subject: Re: [vserver] vhashify not working? - 2.6.27.14-vs2.3.0.36.4
From: "John A. Sullivan III" <jsullivan@opensourcedevel.com>
Date: Tue, 31 Mar 2009 10:10:49 -0400

On Tue, 2009-03-31 at 14:02 +0000, Christoph Lukas wrote:
> [..]
> 
> > > Thank you, Christoph.  The commands show plenty of both types of files
> > > > with the hard links clearly outweighing the regular files.  Strange that
> > > > I still show 20GB for 10 servers.  Take care - John
> > > 
> > > Are you sure that your measurements of disk usage are correct?
> > > Do the 20 GB disk usage correspond with the df output on the /vservers
> > > partition?
> > > 
> > > du -sch /vservers/*
> > > 
> > > should notice multiple hardlinks and count them only once.
> > > 
> > > Regards,
> > > Christoph
> > > 
> > > 
> > Yes, the numbers match and they also match the size of the space
> > consumed on the thinly provisioned ZFS zvol on which they reside (28.1
> > GB):
> > [root@vd01 ~]# du -sch /vservers/*
> > 4.4G    /vservers/cle
> > 2.2G    /vservers/gssstation
> > 2.2G    /vservers/jasstation
> > 1.4G    /vservers/jintra
> > 16K     /vservers/lost+found
> > 1.4G    /vservers/mintra
> > 1.4G    /vservers/mlapo
> > 1.4G    /vservers/simple
> > 1.4G    /vservers/smcc
> > 1.4G    /vservers/tkee
> > 1.4G    /vservers/tvan
> > 1.4G    /vservers/vdb
> > 1.9G    /vservers/vdb2
> > 1.4G    /vservers/vde
> > 1.1M    /vservers/vetc
> > 23G     total
> > 
> > I am guessing this may also affect my memory usage.  Does VServer use
> > the hashify information to determine whether a binary being called into
> > memory already exists? Thanks - John
> 
> After unification identical binaries in different vservers are hardlinks
> to the same inode. Therefore they are the same file / binary from a
> kernel perspective and can reuse cache and memory.
> 
> If your memory usage will be lower with unification depends on if all
> the running binaries are unified or not.
> 
> Regards,
> Christoph
> 
Thanks, that what I thought so this is actually a pretty big issue for
us as we are looking to shoe horn hundreds of guests into our fairly
large servers.  Our challenge is balancing disk, CPU, RAM, and network
I/O.  I think resolving this would work to greatly optimize the first
and third factors and I suppose even the third as these devices are
iSCSI attached and we'd have less disk I/O with fewer files loading into
memory.  I'm really quite ignorant of kernel internals and new to
vserver so any help is greatly appreciated - John
-- 
John A. Sullivan III
Open Source Development Corporation
+1 207-985-7880
jsullivan@opensourcedevel.com

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