Re: [PATCH 2/3] strbuf.h API users: don't hardcode 8192, use STRBUF_HINT_SIZE

Ævar Arnfjörð Bjarmason  [off-list ref] writes:

Change a couple of users of strbuf_init() that pass a hint of 8192 to
pass STRBUF_HINT_SIZE instead.

Both of these hardcoded occurrences pre-date the use of the strbuf
API. See 5242bcbb638 (Use strbuf API in cache-tree.c, 2007-09-06) and
af6eb82262e (Use strbuf API in apply, blame, commit-tree and diff,
2007-09-06).

In both cases the exact choice of 8192 is rather arbitrary, e.g. for
commit buffers I think 1024 or 2048 would probably be a better
default (this commit message is getting this commit close to the
former, but I daresay it's already way above the average for git
commits).

Yes, they are arbitrary within the context of these callers.

I do not think using STRBUF_HINT_SIZE macro in them is the right
thing to do at all, as there is no reason to think that the best
value for the write chunk sizes in these codepath has any linkage to
the best value for the read chunk sizes used by strbuf_read() at
all.  When benchmarking reveals that the best default size for
strbuf_read() is 16k, you'd update STRBUF_HINT_SIZE to 16k, but how
do you tell that it also happens to be the best write buffer size
for the cache-tree writeout codepath (answer: you don't)?