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[35.187.50.168]) by smtp.gmail.com with ESMTPSA id o47sm9750625wrc.7.2018.03.16.12.40.02 (version=TLS1_2 cipher=ECDHE-RSA-CHACHA20-POLY1305 bits=256/256); Fri, 16 Mar 2018 12:40:03 -0700 (PDT) From: Junio C Hamano To: =?utf-8?B?Tmd1eeG7hW4gVGjDoWkgTmfhu41j?= Duy Cc: avarab@gmail.com, e@80x24.org, git@vger.kernel.org, peff@peff.net Subject: Re: [PATCH v4 08/11] pack-objects: shrink z_delta_size field in struct object_entry References: <20180308114232.10508-1-pclouds@gmail.com> <20180316183200.31014-1-pclouds@gmail.com> <20180316183200.31014-9-pclouds@gmail.com> Date: Fri, 16 Mar 2018 12:40:02 -0700 In-Reply-To: <20180316183200.31014-9-pclouds@gmail.com> (=?utf-8?B?Ik5n?= =?utf-8?B?dXnhu4VuIFRow6FpIE5n4buNYw==?= Duy"'s message of "Fri, 16 Mar 2018 19:31:57 +0100") 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: > We only cache deltas when it's smaller than a certain limit. This limit > defaults to 1000 but save its compressed length in a 64-bit field. > Shrink that field down to 16 bits, so you can only cache 65kb deltas. > Larger deltas must be recomputed at when the pack is written down. > > Signed-off-by: Nguyễn Thái Ngọc Duy > --- > if (entry->delta_data && !pack_to_stdout) { > - entry->z_delta_size = do_compress(&entry->delta_data, > - entry->delta_size); > - cache_lock(); > - delta_cache_size -= entry->delta_size; > - delta_cache_size += entry->z_delta_size; > - cache_unlock(); > + unsigned long size; > + > + size = do_compress(&entry->delta_data, entry->delta_size); > + entry->z_delta_size = size; > + if (entry->z_delta_size == size) { It is confusing to readers to write A = B; if (A == B) { /* OK, A was big enough */ } else { /* No, B is too big to fit on A */ } I actually was about to complain that you attempted an unrelated micro-optimization to skip cache_lock/unlock when delta_size and z_delta_size are the same, and made a typo. Something like: size = do_compress(...); if (size < (1 << OE_Z_DELTA_BITS)) { entry->z_delta_size = size; cache_lock(); ... cache_unlock(); } else { FREE_AND_NULL(entry->delta_data); entry->z_delta_size = 0; } would have saved me a few dozens of seconds of head-scratching. > + cache_lock(); > + delta_cache_size -= entry->delta_size; > + delta_cache_size += entry->z_delta_size; > + cache_unlock(); > + } else { > + FREE_AND_NULL(entry->delta_data); > + entry->z_delta_size = 0; > + } > }