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[34.125.197.132]) by smtp.gmail.com with ESMTPSA id b37-20020a631b65000000b00434651f9a96sm11611043pgm.15.2022.09.15.09.36.37 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 15 Sep 2022 09:36:38 -0700 (PDT) Date: Thu, 15 Sep 2022 16:36:36 +0000 From: Minchan Kim To: Sergey Senozhatsky Cc: Andrew Morton , Nitin Gupta , Brian Geffon , linux-kernel@vger.kernel.org, linux-mm@kvack.org Subject: Re: [PATCHv2] zram: do not waste zram_table_entry flags bits Message-ID: References: <20220912152744.527438-1-senozhatsky@chromium.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20220912152744.527438-1-senozhatsky@chromium.org> ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1663259799; h=from:from:sender:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type:content-transfer-encoding: in-reply-to:in-reply-to:references:references:dkim-signature; bh=Bya1RG0oExfDfV/RNQQVlFWpnUEDKrN8oNZxHjwTDWM=; b=hw6DtNOg1lu8nibVT+XIGvRQtHEPWRmnr5+vaYHsKAjTRz5oCLftm9GXxPgdv9RJvXkB4W sARCJWQqPFax6nLu5TgDKs63p3btCVSzpWjk4y5roTPJqPTgjfeLTWIAANMFLYoyZLAoMG gPQUlXd7o+p6WsgiALwfjRBz6f09Dk0= ARC-Authentication-Results: i=1; imf07.hostedemail.com; dkim=pass header.d=gmail.com header.s=20210112 header.b=beMcfXIg; spf=pass (imf07.hostedemail.com: domain of minchan.kim@gmail.com designates 209.85.216.49 as permitted sender) smtp.mailfrom=minchan.kim@gmail.com; dmarc=fail reason="SPF not aligned (relaxed), DKIM not aligned (relaxed)" header.from=kernel.org (policy=none) ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1663259799; a=rsa-sha256; cv=none; b=Auf3GrYBxYZTjTeenbDlV9te/htTiQfr0x4SmVd7etr87yIJbxcEIm/ojaK2/LZoFzXAg8 i8BJ5MNVmCrZxC6/0Ldfy+pnYvz6O5nIz1XkwI0PTLPHz+ZbKR/E0ti0YUzR3RXKzgAY4u du1MpTDVBblcUGtg9muXq/97S9lNCFo= X-Stat-Signature: 1gmoemkyggc17871jcqm8wk6qfdnw5d7 X-Rspamd-Queue-Id: AD60840097 X-Rspam-User: Authentication-Results: imf07.hostedemail.com; dkim=pass header.d=gmail.com header.s=20210112 header.b=beMcfXIg; spf=pass (imf07.hostedemail.com: domain of minchan.kim@gmail.com designates 209.85.216.49 as permitted sender) smtp.mailfrom=minchan.kim@gmail.com; dmarc=fail reason="SPF not aligned (relaxed), DKIM not aligned (relaxed)" header.from=kernel.org (policy=none) X-Rspamd-Server: rspam06 X-HE-Tag: 1663259799-495865 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: On Tue, Sep 13, 2022 at 12:27:44AM +0900, Sergey Senozhatsky wrote: > zram_table_entry::flags stores object size in the lower bits and > zram pageflags in the upper bits. However, for some reason, we > use 24 lower bits, while maximum zram object size is PAGE_SIZE, > which requires PAGE_SHIFT bits (up to 16 on arm64). This wastes > 24 - PAGE_SHIFT bits that we can use for additional zram pageflags > instead. > > Also add a BUILD_BUG_ON() to alert us should we run out of bits > in zram_table_entry::flags. > > Signed-off-by: Sergey Senozhatsky Acked-by: Minchan Kim