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[35.187.50.168]) by smtp.gmail.com with ESMTPSA id l38sm8191136wrc.96.2018.03.01.10.00.52 (version=TLS1_2 cipher=ECDHE-RSA-CHACHA20-POLY1305 bits=256/256); Thu, 01 Mar 2018 10:00:52 -0800 (PST) From: Junio C Hamano To: =?utf-8?B?Tmd1eeG7hW4gVGjDoWkgTmfhu41j?= Duy Cc: git@vger.kernel.org, Jeff King , Eric Wong Subject: Re: [PATCH 04/11] pack-objects: use bitfield for object_entry::depth References: <20180228092722.GA25627@ash> <20180301091052.32267-1-pclouds@gmail.com> <20180301091052.32267-5-pclouds@gmail.com> Date: Thu, 01 Mar 2018 10:00:52 -0800 In-Reply-To: <20180301091052.32267-5-pclouds@gmail.com> (=?utf-8?B?Ik5n?= =?utf-8?B?dXnhu4VuIFRow6FpIE5n4buNYw==?= Duy"'s message of "Thu, 1 Mar 2018 16:10:45 +0700") Message-ID: User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/25.2.50 (gnu/linux) MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 8bit Sender: git-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: git@vger.kernel.org Nguyễn Thái Ngọc Duy 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 > --- 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 */ > };