Re: Something's eating my memory...

[Bruce Ferrell <bferrell@baywinds.org>]

When I run into this type of problem, I turn to sysstat.  I use it in 
conjunction with bigbrother/larrd/rrdtool and a bigbrother plugin called 
bb-sar from www.deadcat.net.

I almost missed the nfs aspect of this.  Is the system load suddenly sky 
rocketing?  I would start looking for something NFS has exported being 
"taken" away.  I saw something similar to this on a mail server with 
autofs mounted home directories.  We had an admin who liked to rearrange 
home directories.  It caused the system to get very confused and be very 
unhappy as NFS, even with soft mounts and interruptable flags set would 
keep pounding for the old, missing location.

This doesn't look like a memory allocation problem at all.  If kernel 
logging isn't enabled, enable it.  You'll get some good clues there.

Paul Furness wrote:
> Hi.
> 
> Can someone help me? I'm running out of memory on my production server,
> and I can't figure out exactly why.
> 
> It's a pretty new machine (about 4 months old), and the spec is: dual
> 2.8GHz Xeon CPU, 1G memory, SCSI hard disks, and an external SCSI RAID
> controller. It is based on a build of RedHat 7.3 + redhat released
> patches, and I have added the 2.4.21 kernel patched to support LVM and
> XFS. 
> 
> The primary (only?!) job of the serve is to be a file server, offering
> nfs and samba shares to servers and workstations; this includes the
> users' home directories.
> 
> When I first built it, it worked like a dream, but of course it wasn't
> under a big load. Over time (about a month) I ramped up the load by
> adding the various shares to the machine and making them available to
> users.
> 
> Over the last week, there have been a number of occasions when it ground
> almost to a complete halt; the rest of the time it performed just fine.
> It looks like it's having trouble when it gets hammered by everyone
> logging out at the end of the day (We have roaming profiles on windows
> workstations, using a samba domain controller. As an aside: it works
> really well; I can't imagine why anyone would ever want an actual
> windows server... ;). Anyhow, this heavy loading is to be expected.
> 
> When I run top or free, it tells me that almost all of the memory is
> used, but it doesn't seem to be actually used by anything; the total
> memory used by the processes that top is showing is about 80M. Buffers
> is showing up as anything between about 450M and 700M.  Clearly, the
> performance issue is happening when the memory fills up and it starts
> swapping. Here's an example output from free:
> 
>                  total       used       free     shared    buffers    
> cached
>     Mem:       1032104    1019200      12904          0       2100    
> 342172
>     -/+ buffers/cache:     674928     357176
>     Swap:      2096472       3508    2092964
> 
> I don't mind putting more memory into the server if this is the
> solution, but I need to be sure that it will actually help - if I put in
> another G and it fills up just the same, I'm back where I started but a
> little bit poorer!
> 
> My problems are: 
> 1. I don't really understand how the buffers are allocated, or why, and
> whether changing this would help performance.
> 2. There seems to be at least 150-200M of memory that I can't account
> for. 
> 
> Can anyone point me to where I can find out about the buffers, what they
> are and how they work? 
> 
> Can anyone suggest some accurate performance monitoring software that I
> can use to find out what exactly is happening when the server grinds to
> a halt? I guess I really need to know where the memory is going and
> possibly the disk activity. Gkrellm is sort of useful, but I really need
> something a bit more determined :)
> 
> As always, any and all suggestions much appreciated.
> 
> Paul.
> 
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