Re: 2.6.25-rc3: 34TB vmalloc total -- overflow in /proc/meminfo?

[Hugh Dickins]

On Wed, 5 Mar 2008, Christian Kujau wrote:
> On Wed, 5 Mar 2008, Pavel Machek wrote:
> > CommitLimit:   4132360 kB
> > Committed_AS:    27684 kB
> > VmallocTotal: 34359738367 kB
> > VmallocUsed:     18112 kB
> > VmallocChunk: 34359720115 kB

I don't see what Pavel's issue is with this: it's simply a fact that
with a 64-bit kernel, we've lots of virtual address space to spare
for vmalloc.  What would be surprising is for VmallocUsed to get up
as high as that.

> 
> out of curiosity: yesterday I've seen a box[0] with ~4 TB Committed_AS:
> 
> CommitLimit:   3085152 kB
> Committed_AS: 4281048084 kB
> VmallocTotal:   118776 kB
> VmallocUsed:     13772 kB
> VmallocChunk:   103880 kB
> 
> Since it's a rather old kernel (2.6.19.2), I just want to know: could this be
> related to what you've seen or this completely different

Completely different and much more interesting.

> (and Committed_AS is
> just this high because some st00pid app has allocated this much memory but not
> freed again)?

Unlikely.  Offhand I'm not quite sure that's impossible, but it's far
more likely that we've a kernel bug and vm_committed_space has wrapped
negative.

Ancient as your kernel is, I don't notice anything in the ChangeLogs
since then to say we've fixed a bug of that kind since 2.6.19.
Any idea how to reproduce this?  Are you using HugePages at all?
(It's particularly easy for us to get into a muddle over them,
though historically I think mremap has proved most difficult for
Committed_AS accounting).

Thanks,
Hugh

> 
> Thanks,
> Christian.
> 
> [0] amd64, 32bit kernel, 32bit userland, 4GB RAM
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