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[2620:137:e000::1:20]) by mx.google.com with ESMTP id c9-20020aa7c749000000b004612915d21bsi8294747eds.276.2022.11.14.08.55.42; Mon, 14 Nov 2022 08:56:03 -0800 (PST) Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20; Authentication-Results: mx.google.com; spf=pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S236631AbiKNPdP (ORCPT + 87 others); Mon, 14 Nov 2022 10:33:15 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:55382 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S234803AbiKNPdO (ORCPT ); Mon, 14 Nov 2022 10:33:14 -0500 Received: from dfw.source.kernel.org (dfw.source.kernel.org [IPv6:2604:1380:4641:c500::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 17E572CC91 for ; Mon, 14 Nov 2022 07:33:14 -0800 (PST) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by dfw.source.kernel.org (Postfix) with ESMTPS id AA9B561224 for ; Mon, 14 Nov 2022 15:33:13 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 341DBC433D6; Mon, 14 Nov 2022 15:33:12 +0000 (UTC) Date: Mon, 14 Nov 2022 10:33:50 -0500 From: Steven Rostedt To: Gautam Menghani Cc: akpm@linux-foundation.org, mhiramat@kernel.org, shy828301@gmail.com, zokeefe@google.com, david@redhat.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v3] mm/khugepaged: add tracepoint to collapse_file() Message-ID: <20221114103350.4b8a2786@gandalf.local.home> In-Reply-To: <20221026052218.148234-1-gautammenghani201@gmail.com> References: <20221026052218.148234-1-gautammenghani201@gmail.com> X-Mailer: Claws Mail 3.17.8 (GTK+ 2.24.33; x86_64-pc-linux-gnu) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit X-Spam-Status: No, score=-6.7 required=5.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,RCVD_IN_DNSWL_HI,SPF_HELO_NONE,SPF_PASS autolearn=ham autolearn_force=no version=3.4.6 X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on lindbergh.monkeyblade.net Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, 26 Oct 2022 10:52:18 +0530 Gautam Menghani wrote: Ideally we want the trace event structure to be as packed as possible to not waste space on the ring buffer. > + TP_ARGS(mm, hpage, index, is_shmem, addr, file, nr, result), > + TP_STRUCT__entry( > + __field(struct mm_struct *, mm) 4 / 8 bytes (depending on 32 bit or 64 bit arch) > + __field(unsigned long, hpfn) 4 / 8 bytes The two above is fine. > + __field(pgoff_t, index) 4 / 8 bytes > + __field(bool, is_shmem) 4 bytes (or less) > + __field(unsigned long, addr) 4 / 8 bytes > + __string(filename, file->f_path.dentry->d_iname) 4 bytes > + __field(int, nr) 4 bytes > + __field(int, result) 4 bytes For best packing, it's best to keep long / pointers together, and ints and bools together (or paired). On 64 bit archs, there is likely to be a 4 byte hole between is_shmem and addr. > + ), > + Better to have it be: TP_STRUCT__entry( __field(struct mm_struct *, mm) __field(unsigned long, hpfn) __field(pgoff_t, index) __field(unsigned long, addr) __field(bool, is_shmem) __string(filename, file->f_path.dentry->d_iname) __field(int, nr) __field(int, result) ), Where I swapped is_shmem and addr. -- Steve