From patchwork Wed Nov 10 16:23:17 2021 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Geert Uytterhoeven X-Patchwork-Id: 12612461 X-Patchwork-Delegate: geert@linux-m68k.org Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id C1A3FC433FE for ; Wed, 10 Nov 2021 16:23:27 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id A6EC761246 for ; Wed, 10 Nov 2021 16:23:27 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230006AbhKJQ0M (ORCPT ); Wed, 10 Nov 2021 11:26:12 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:40042 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229602AbhKJQ0K (ORCPT ); Wed, 10 Nov 2021 11:26:10 -0500 Received: from laurent.telenet-ops.be (laurent.telenet-ops.be [IPv6:2a02:1800:110:4::f00:19]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id E374CC061767 for ; Wed, 10 Nov 2021 08:23:22 -0800 (PST) Received: from ramsan.of.borg ([IPv6:2a02:1810:ac12:ed20:9dc9:efd5:4c6f:baa9]) by laurent.telenet-ops.be with bizsmtp id GgPK2600C1LAWtA01gPKaH; Wed, 10 Nov 2021 17:23:20 +0100 Received: from rox.of.borg ([192.168.97.57]) by ramsan.of.borg with esmtps (TLS1.3) tls TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384 (Exim 4.93) (envelope-from ) id 1mkqNb-00BUyT-26; Wed, 10 Nov 2021 17:23:19 +0100 Received: from geert by rox.of.borg with local (Exim 4.93) (envelope-from ) id 1mkqNa-007g1r-LI; Wed, 10 Nov 2021 17:23:18 +0100 From: Geert Uytterhoeven To: Rob Herring , Frank Rowand Cc: devicetree@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linuxppc-dev@lists.ozlabs.org, linux-mips@vger.kernel.org, linux-riscv@lists.infradead.org, linux-renesas-soc@vger.kernel.org, linux-kernel@vger.kernel.org, Geert Uytterhoeven Subject: [PATCH/RFC] of: Shrink struct of_device_id Date: Wed, 10 Nov 2021 17:23:17 +0100 Message-Id: X-Mailer: git-send-email 2.25.1 MIME-Version: 1.0 Precedence: bulk List-ID: X-Mailing-List: linux-renesas-soc@vger.kernel.org Currently struct of_device_id is 196 (32-bit) or 200 (64-bit) bytes large. It contains fixed-size strings for a name, a type, and a compatible value, but the first two are barely used. OF device ID tables contain multiple entries, plus an empty sentinel entry. Statistics for my current kernel source tree: - 4487 tables with 16836 entries (3367200 bytes) - 176 names (average 6.7 max 23 chars) - 66 types (average 5.1 max 21 chars) - 12192 compatible values (average 18.0 max 45 chars) Taking into account the minimum needed size to store the strings, only 6.9% of the allocated space is used... Reduce kernel size by reducing the sizes of the fixed strings by one half. This reduces the size of an ARM multi_v7_defconfig kernel by ca. 400 KiB. For a typical kernel supporting a single board, you can expect to save 50-100 KiB. Signed-off-by: Geert Uytterhoeven --- Notes: - While gcc complains if the non-NUL characters in a string do not fit in the available space, it does not complain if there is no space to store the string's NUL-terminator. However, that should be caught during testing, as the affected entry won't ever match. The kernel won't crash, as such strings will still be terminated by the sentinel in the table. - We could save even more by converting the strings from fixed-size arrays to pointers, at the expense of making it harder to mark entries __init. Given most drivers support binding and unbinding and thus cannot use __init for of_device_id tables, perhaps that's the way to go? Thanks for your comments! --- include/linux/mod_devicetable.h | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-) diff --git a/include/linux/mod_devicetable.h b/include/linux/mod_devicetable.h index ae2e75d15b219920..2bb2558d52d30d2b 100644 --- a/include/linux/mod_devicetable.h +++ b/include/linux/mod_devicetable.h @@ -266,9 +266,9 @@ struct sdw_device_id { * Struct used for matching a device */ struct of_device_id { - char name[32]; - char type[32]; - char compatible[128]; + char name[24]; + char type[24]; + char compatible[48]; const void *data; };