Re: [PATCH 6/6] pack-objects: reuse on-disk deltas for thin "have" objects

From: Junio C Hamano <gitster@pobox.com>
Date: Aug 20, 2018, 21:03 UTC
Message-ID: <xmqqa7pgbvie.fsf@gitster-ct.c.googlers.com>
In-Reply-To: <20180817210604.GF20088@sigill.intra.peff.net>

Jeff King <peff@peff.net> writes:

> And that's exactly what this patch does: when we're
> considering whether to reuse an on-disk delta, if bitmaps
> tell us the other side has the object (and we're making a
> thin-pack), then we reuse it.

That's really the natural extension and logical consequence of the "reuse existing deltas" mechanism from Feb 2006 ;-)

Show 11 quoted lines

> So taking all of those options into account, what I ended up
> with is a separate list of "external bases" that are not
> part of the main packing list. Each delta entry that points
> to an external base has a single-bit flag to do so; we have a
> little breathing room in the bitfield section of
> object_entry.
>
> This lets us limit the change primarily to the oe_delta()
> and oe_set_delta_ext() functions. And as a bonus, most of
> the rest of the code does not consider these dummy entries
> at all, saving both runtime CPU and code complexity.

Tricky ;-)

I wonder if we can move the preferred base objects that we are not going to send also off of the "main packing list" to this new mechanism?

> +static struct bitmap_index *bitmap_git;
> ...
> +static int thin = 0;

Please trust what BSS will do to your static vars.