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Mon, 15 Dec 2025 16:59:56 -0800 (PST) Received: from google.com ([2a00:79e0:2031:6:88fa:c762:fe19:6db7]) by smtp.gmail.com with ESMTPSA id 41be03b00d2f7-c0c2c963b53sm13573171a12.36.2025.12.15.16.59.54 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 15 Dec 2025 16:59:56 -0800 (PST) Date: Tue, 16 Dec 2025 09:59:51 +0900 From: Sergey Senozhatsky To: Brian Geffon Cc: Sergey Senozhatsky , Andrew Morton , Minchan Kim , David Stevens , linux-kernel@vger.kernel.org, linux-mm@kvack.org, linux-block@vger.kernel.org Subject: Re: [PATCH 1/3] zram: use u32 for entry ac_time tracking Message-ID: References: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Stat-Signature: 3c6dqzs6uu689954za5rso488oncn96p X-Rspam-User: X-Rspamd-Server: rspam07 X-Rspamd-Queue-Id: C5ED020002 X-HE-Tag: 1765846797-808300 X-HE-Meta: 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 bpGG50bn mqgFDL+NUGim9QBMkhw7jNRGIUoU1+hHj/xq+soWo1ZNy3C8tOlSNpLWSbwf+RGphaJrOmMTfbN655L1GwH7kD6B88otQ4/Gq355uYPDmIze3eegL5tudHFUKy1Si7WF6pO/S049zrUsxes+igJlWwMYUJoPqddBo6qOecYCLuc7lcG65Rrhow/IDeL1mkIra7tTN0pTYKziae6eNZ6TtYZgNaZhXPrB7IXI1jsGKWs8aId0TAKYKgBhNUn1lPcsQqAEVle2UM55cd1LzaN8BX6yLOnMKfNGZalne/hq/6Yq6qX3dnk6u+ZgInS1RjWlShUjPhH5/32tqsKHqdvvYKhZsfWjFTxZ85d5fObQzAUHoPHQGWnOdj5s4fxAfu3j/eYFKRd/fX5sjL97IZQaZkK5Ckg== X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On (25/12/15 17:31), Brian Geffon wrote: [..] > > struct zram_table_entry { > > unsigned long handle; > > - unsigned long flags; > > + union { > > + unsigned long __lock; > > + struct attr { > > + u32 flags; > > #ifdef CONFIG_ZRAM_TRACK_ENTRY_ACTIME > > - ktime_t ac_time; > > + u32 ac_time; > > #endif > > Why not just always enable CONFIG_ZRAM_TRACK_ENTRY_ACTIME now that it > doesn't consume any additional space? It's "free" only on x64. On 32bit systems the removal of ZRAM_TRACK_ENTRY_ACTIME will unconditionally add 4 bytes per zram_table_entry. > Also, why can't we do this with a single unsigned long flags > as before and have a simple method that isolates and casts the > lower 32bits as a u32? There are no upper and lower 32 bits in unsigned long on 32bit systems.