On Wed, 11 Jun 2008, Ben Lynn wrote:
>
> I don't think the memcmp is slow. I think the ce_modified_check_fs in:
>
> smudge() {
> ...
> if (ce_match_stat_basic(ce, &st))
> return;
> if (ce_modified_check_fs(ce, &st))
> ce->ce_size = 0;
> }
>
> is potentially slow, and I'm saying you could replace it with
>
> smudge() {
> ...
> if (ce_match_stat_basic(ce, &st))
> return;
> ce->ce_size = ~0;
> }
>
> to avoid the ce_modified_check_fs call. But it is an unclean solution,
> which is why I champion having an extra flag per file.
Well, you have to think about what you want to optimize here.
The thing we want to optimize is not the writing of the index file, but
the subsequent _use_ of it!
As such, the last thing we actually want to do is to smudge the index file
entry. If it actually has a possibility of being not smudged, we're much
better off saying "hey, now the index file is newer, and the file it
refers to is all good!"
That way, we won't have to do the ce_modified_check_fs() call later - we
do it just once, and the file is up-to-date.
So we don't want to smudge it, but if the stat information says it migth
match even though it doesn't, we have to. But if the stat information says
it matches, and the data actually _does_ match, then we shouldn't smudge
it, we should be happy - and all subsequent users of the index will then
know that they don't even need to look at the file contents.
Linus
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