Re: [linux-mm-cc] Announce: ccache release 0.1

["Nitin Gupta" <nitingupta910@gmail.com>]

On Feb 19, 2008 6:37 PM, John McCabe-Dansted <gmatht@gmail.com> wrote:
> On Feb 19, 2008 9:06 PM, Nitin Gupta <nitingupta910@gmail.com> wrote:
> > On Feb 19, 2008 4:03 PM, John McCabe-Dansted <gmatht@gmail.com> wrote:
> > > On Feb 19, 2008 6:39 AM, Nitin Gupta <nitingupta910@gmail.com> wrote:
> > > > Some performance numbers for allocator and de/compressor can be found
> > > > on project home. Currently it is tested on Linux kernel 2.6.23.x and
> > > > 2.6.25-rc2 (x86 only). Please mail me/mailing-list any
> > > > issues/suggestions you have.
> > >
> > > It caused Gutsy (2.6.22-14-generic) to crash when I did a swap off of
> > > my hdd swap. I have a GB of ram, so I would have been fine without
> > > ccache.
> >
> > These days "desktops with small memory" probably means virtual
> > machines with, say, <512M RAM :-)
>
> The Hardy liveCD is really snappy with a 192MB VM and and a 128MB
> ccache swap. :)
>

Good to know :)

> > > I had swapped on a 400MB ccache swap.
> > >
> >
> > I need /var/log/messages (or whatever file kernel logs to in Gutsy) to
> > debug this.
> > Please send it to me offline if its too big.
>
> This seems to be the bit you want:
>

Unfortunately none of these messages suggest why crash happened.
If you can send entire log, that will probably be more useful.


> ubuntu-xp syslogd 1.4.1#21ubuntu3: restart.
> Feb 19 08:07:31 ubuntu-xp -- MARK --
> ...
> Feb 19 18:47:31 ubuntu-xp -- MARK --
> Feb 19 18:59:51 ubuntu-xp kernel: [377208.185464] ccache: Unknown
> symbol lzo1x_decompress_safe
<snip>

All these 'Unknown symbol' messages are because you tried loading
ccache.ko module before tlsf.ko and lzo*.ko modules.

>
> > > BTW, why is the default 10% of mem?
> >
> > I have no great justification for "10%".
>
> Perhaps 100% (or maybe 50%) would be a more sensible default? For me
> 66% makes a huge difference to the Hardy liveCD performance. 10% makes
> a difference but 50%+ goes from "ls /" taking 10s to snappy
> performance even on large applications like Firefox.
>

I think this depends a lot on kind of workload and system. For e.g:
- On desktops, retaining too many anonymous pages at cost of
continuously losing page-cache (filesystem-backed) pages can hurt
performance for workload that repeatedly access same file(s).
- On embedded systems, too much de/compression will drain all battery.
and so on...

Also, I don't know which of  these use cases is more "common".

- Nitin

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