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

[John McCabe-Dansted]

On Fri, Feb 22, 2008 at 5:38 PM, Nitin Gupta <nitingupta910 at gmail.com> wrote:
>  >  I was thinking that for the LiveCD case the primary performance hit
>  >  would be seeking on the CD drive. Hence to maximize memory available
>  >  for caching the CD, we should
>  >    1) Use 100% mem for compcache.
>
>  Agree.
>
>  >    2) Set compcaches priority to be low, so that hdd swap will be used
>  >  first if it exists.
>  >  Does this seem reasonable?
>
>  Setting compcache prio < hdd swap will not be good. After all,
>  compcache can potentially avoid swapping to slow hard-disks improving
>  system performance significantly. If compcache is not sufficient to
>  store all pages then only we should let it go to lower prio swaps.

I like the idea of not touching the harddisk for a different reason:
we may be using the LiveCD because there is something dogdy about the
harddisk. If we avoid using the swap on the harddisk, we limit our
vulnerability to harddisk failures and reduce the probability we will
clobber valuable data if the partition table is corrupt.

However, AFAICT, with huge compcaches we could chew up a lot of memory
that could be used to cache the LiveCD. If /dev/compcache is 100% and
stuff compresses poorly we could have almost 100% of memory used
before swapping to disk? Even the expect 50% of ram being used seems
far too much given how much faster harddisks are than CDs.

It seems that we really want two compcaches: 10% high-priority
compcache and 90% low-priority compcache, with as much harddisk swap
as we can find in the middle.

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