Re: performance problem: "git commit filename"

Linus Torvalds [off-list ref] writes:

HOWEVER. This was just a quick hack, and while it all looks sane, this is 
some damn core code. Somebody else should double- and triple-check this.

Double-checked.  The patch looks sane.

[ That 4x lstat thing bothers me. I think we should add a flag to the 
  index saying "we checked this once already, it's clean", so that if we 
  do multiple passes over the index, we can still do just a single lstat() 
  on just the first pass. But that's a separate issue.

I've thought about this in a different context before, but it
seemed quite tricky, as some codepaths in more complex commands
(commit being one of them) tend to use the cache and discard to
use it for different purpose (like creating temporary index and
then reading the real index).  Besides, I had an impression that
we ran out of the bits of ce_flags in the cache entry, although
we could shorten the maximum path we support from 4k down to 2k
bytes.  I'll have to think about this a bit more.