Nguyễn Thái Ngọc Duy <pclouds@xxxxxxxxx> writes:
> This does not give us any saving due to padding. But we will be able
> to save once we cut 4 bytes out of this struct in a subsequent patch.
>
> Because of struct packing from now on we can only handle max depth
> 4095 (or even lower when new booleans are added in this struct). This
> should be ok since long delta chain will cause significant slow down
> anyway.
>
> Signed-off-by: Nguyễn Thái Ngọc Duy <pclouds@xxxxxxxxx>
> ---
This should be marked as RFC/PATCH; I do not have objection to
limiting the delta depth to some reasonable length (rather than the
current 1<<31 or worse 1<<63), and 4k may be such a reasonable limit
(I'd actually think anything more than a few hundreds is probably a
bad idea), but it needs to be documented.
> builtin/pack-objects.c | 4 ++++
> pack-objects.h | 6 ++----
> 2 files changed, 6 insertions(+), 4 deletions(-)
>
> diff --git a/builtin/pack-objects.c b/builtin/pack-objects.c
> index a4dbb40824..cfd97da7db 100644
> --- a/builtin/pack-objects.c
> +++ b/builtin/pack-objects.c
> @@ -3068,6 +3068,10 @@ int cmd_pack_objects(int argc, const char **argv, const char *prefix)
> if (pack_to_stdout != !base_name || argc)
> usage_with_options(pack_usage, pack_objects_options);
>
> + if (depth > (1 << OE_DEPTH_BITS))
> + die(_("delta chain depth %d is greater than maximum limit %d"),
> + depth, (1 << OE_DEPTH_BITS));
> +
> argv_array_push(&rp, "pack-objects");
> if (thin) {
> use_internal_rev_list = 1;
> diff --git a/pack-objects.h b/pack-objects.h
> index fca334ab4d..3941e6c9a6 100644
> --- a/pack-objects.h
> +++ b/pack-objects.h
> @@ -2,6 +2,7 @@
> #define PACK_OBJECTS_H
>
> #define OE_DFS_STATE_BITS 2
> +#define OE_DEPTH_BITS 12
>
> /*
> * State flags for depth-first search used for analyzing delta cycles.
> @@ -43,10 +44,7 @@ struct object_entry {
> unsigned tagged:1; /* near the very tip of refs */
> unsigned filled:1; /* assigned write-order */
> unsigned dfs_state:OE_DFS_STATE_BITS;
> -
> - /* XXX 20 bits hole, try to pack */
> -
> - int depth;
> + unsigned depth:OE_DEPTH_BITS;
>
> /* size: 120, padding: 4 */
> };
