[linux-mm-cc] Fixing out-of-memory errors on LiveCDs.

[Nitin Gupta]

On 3/24/07, John McCabe-Dansted <gmatht at gmail.com> wrote:
> " - LiveCD environments: Here, the swap space might not even be
> available. Also, CD-ROM access is extremely slow. Thus, large no. of
> programs can be pre-fetched and compressed in memory resulting in much
> better performance."
>
> Would it also be possible to expand the amount of virtual memory
> available without needing a swap partition on disk?
>

Sorry for late reply.

Yes, you can have virtually larger RAM with ccaching but there is a
problem. All the pages taken by ccache are pinned in memory so we get
OOM kills even before than the case of vanilla kernel.

So, what is required is to empty out the ccache before we resort to
OOM kills. This is yet to be done (next release?)

> (Even if the user attempts to load /dev/rand into memory, we can
> probably rely on reclaiming 32MB by compressing Gnome's memory
> structures etc.)
>
> I ask because Ubuntu was having some problems with the LiveCD
> partition tool running out of memory (because it had to run before the
> swap partition was set up). In theory the Ubuntu LiveCD supports
> systems with 256MB of ram, however they were having problems with
> video cards stealing main memory for use as video ram.
>

Interesting scenario!  It's worth trying ccaching here. In cases where
pages compressed are actually used soon after they are compressed, we
_delay_ the OOM killer. But if these compressed pages are never
requested it pre-pones OOM. So, until we have automatic eviction of
unused compressed pages, it's bit of luck to benefit from ccaching.

Also, I am working on getting ccaching to upcoming 2.6.21 kernel. This
will have some important bug fixes, code cleanups and code
infrastructure to get started with dynamic ccache resizing.


Cheers,
Nitin

> --
> John C. McCabe-Dansted
> PhD Student
> University of Western Australia
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