Re: [RFC PATCH v2 1/4] object: remove "used" field from struct object

From: Junio C Hamano <gitster@pobox.com>
Date: Jul 20, 2017, 21:20 UTC
Message-ID: <xmqqk232kdoo.fsf@gitster.mtv.corp.google.com>
In-Reply-To: <0eb270f40095f132bf9383f230506e45d895e5e1.1500508695.git.jonathantanmy@google.com>

Jonathan Tan <jonathantanmy@google.com> writes:

Show 9 quoted lines

> The "used" field in struct object is only used by builtin/fsck. Remove
> that field and modify builtin/fsck to use a flag instead.
>
> Signed-off-by: Jonathan Tan <jonathantanmy@google.com>
> ---
>  builtin/fsck.c | 24 ++++++++++++++----------
>  object.c       |  1 -
>  object.h       |  2 +-
>  3 files changed, 15 insertions(+), 12 deletions(-)

I vaguely recall trying to do this myself a few years ago. We can easily spot places within this file that does things like this:

> -	obj->flags = HAS_OBJ;

and correctly update it to this:

> +	obj->flags &= ~(REACHABLE | SEEN);
> +	obj->flags |= HAS_OBJ;

but I didn't do so because I was hesitant having to validate, and having to maintain the invariant forever, that anything called from these codepaths is always careful not to clobber the USED bit.

Looks like a reasonable preparatory clean-up that probably should be doable and should be done way before the main part of the series to me. Will queue, together with your other fsck change.

Thanks.