Re: diffcore-rename performance mode

On Tue, Sep 25, 2007 at 09:32:31PM +0200, David Kastrup wrote:

quoted

                 | stock | nofree | old somefree | fixed somefree
-----------------|-----------------------------------------------
user time (s)    | 76.78 | 16.96  | 46.26        | 16.99
peak memory (Kb) | 52300 | 66796  | 59156        | 57328

So now we're at a 4.5x speedup for about 10% extra memory usage. Patch
will follow.

Sounds good except when we happen to just hit the "memory working set
exceeds physical memory" sweet spot.  But the odds are much better
than for "nofree".

Of course, there is the possibility that it is the 10% that pushes you
into swap (or kills your ability to cache the entire pack in RAM).
However, this is probably not a big deal for two reasons:
  1. this is a 50M process handling the linux-2.6 repository. Other
     operations such as repacking already consume significantly more
     memory (git-repack -a allocates 290M on the same repo).
  2. I specifically turned off rename limiting (-l0) to do rename
     detection on these large-ish diffs.  If you have a machine which is
     on the cusp of swapping, then don't do that. Jumping from -l100
     (the default) to -l0 in my tests is _already_ moving you from 28M
     to 52M, a much larger jump.

-Peff