From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-1.1 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS,URIBL_BLOCKED autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id B6722C433E0 for ; Mon, 29 Jun 2020 21:51:52 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 96FCF206A5 for ; Mon, 29 Jun 2020 21:51:52 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=linutronix.de header.i=@linutronix.de header.b="IKXYGJmt"; dkim=permerror (0-bit key) header.d=linutronix.de header.i=@linutronix.de header.b="5bCsnwV2" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2404572AbgF2Vvu (ORCPT ); Mon, 29 Jun 2020 17:51:50 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:40980 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2404569AbgF2Vvo (ORCPT ); Mon, 29 Jun 2020 17:51:44 -0400 Received: from galois.linutronix.de (Galois.linutronix.de [IPv6:2a0a:51c0:0:12e:550::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id D1C73C061755 for ; Mon, 29 Jun 2020 14:51:44 -0700 (PDT) From: John Ogness DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020; t=1593467502; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=siVZWIEnwE41C7ZxHsZfQ8/Re56UAlzQKcSRDT+JiwE=; b=IKXYGJmt9+3Ei4t1+Bz9jNVCq5EyBhJN4FxcPlnhlriH3eqv1MsTGz+xRnHdHDt0MdwjAZ GgC/iiIB5osdzoNnLhSWN8WopSY5+H2icQKjzEAsbVzPTQEvwT7j3BiGUke+vmxAisBCVf ncxdG+J5IclAPaNTpWyACqalFl+HvjJ18ehxf14FR5l9si8QVQiNGyyhqKcCaRzp+bSlCe 3HfQdz2WnIxanWg9QdWnbTdRRUl9QUALzpFJOp88k2eTtqHX97GFc/zeFuG8FQcH+itufC GKq9M863SUY4Byx3DH2OO1kBh+nuTCBoYmmih+2F1/feVSJ0c4MP5ERnCyZ7uw== DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020e; t=1593467502; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=siVZWIEnwE41C7ZxHsZfQ8/Re56UAlzQKcSRDT+JiwE=; b=5bCsnwV2vmOJbIXbrSqZo66YzWmyOSG5xc215ieN3Sqv6ET2KdOCpBcPMjC/fZH1IV3ZcL GMnrZcN4JNSoE9AA== To: Petr Mladek Cc: Peter Zijlstra , Sergey Senozhatsky , Sergey Senozhatsky , Steven Rostedt , Linus Torvalds , Greg Kroah-Hartman , Andrea Parri , Thomas Gleixner , Paul McKenney , kexec@lists.infradead.org, linux-kernel@vger.kernel.org Subject: Re: syslog size unread: was: [PATCH v3 3/3] printk: use the lockless ringbuffer References: <20200618144919.9806-1-john.ogness@linutronix.de> <20200618144919.9806-4-john.ogness@linutronix.de> <20200625152042.GI8444@alley> Date: Mon, 29 Jun 2020 23:51:40 +0200 In-Reply-To: <20200625152042.GI8444@alley> (Petr Mladek's message of "Thu, 25 Jun 2020 17:20:42 +0200") Message-ID: <87k0zp8rrn.fsf@jogness.linutronix.de> MIME-Version: 1.0 Content-Type: text/plain Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2020-06-25, Petr Mladek wrote: > On Thu 2020-06-18 16:55:19, John Ogness wrote: >> --- a/kernel/printk/printk.c >> +++ b/kernel/printk/printk.c >> @@ -1609,11 +1633,15 @@ int do_syslog(int type, char __user *buf, int len, int source) >> break; >> /* Number of chars in the log buffer */ >> case SYSLOG_ACTION_SIZE_UNREAD: >> + if (source != SYSLOG_FROM_PROC) { >> + text = kmalloc(LOG_LINE_MAX + PREFIX_MAX, GFP_KERNEL); >> + if (!text) >> + return -ENOMEM; > > The buffer is needed only to count lines to count the size of added > prefixes. Could we use the new prb_read_valid_info() that allows to > get the number of lines without actually reading the buffer? Yes! For the next version I introduce a macro to iterate just the meta data: #define prb_for_each_info(from, rb, s, i, lc) \ for ((s) = from; prb_read_valid_info(rb, s, i, lc); (s) = (i)->seq + 1) This can be used in all 3 locations where prb_count_lines() is used. In all three places, there is no need to be copying the data. And for SYSLOG_ACTION_SIZE_UNREAD, there is no need for the record and kmalloc'd buffer. This also means that prb_count_lines() will become a private static helper of the ringbuffer. John Ogness From mboxrd@z Thu Jan 1 00:00:00 1970 Return-path: Received: from galois.linutronix.de ([2a0a:51c0:0:12e:550::1]) by merlin.infradead.org with esmtps (Exim 4.92.3 #3 (Red Hat Linux)) id 1jq1go-0003oT-1V for kexec@lists.infradead.org; Mon, 29 Jun 2020 21:51:46 +0000 From: John Ogness Subject: Re: syslog size unread: was: [PATCH v3 3/3] printk: use the lockless ringbuffer References: <20200618144919.9806-1-john.ogness@linutronix.de> <20200618144919.9806-4-john.ogness@linutronix.de> <20200625152042.GI8444@alley> Date: Mon, 29 Jun 2020 23:51:40 +0200 In-Reply-To: <20200625152042.GI8444@alley> (Petr Mladek's message of "Thu, 25 Jun 2020 17:20:42 +0200") Message-ID: <87k0zp8rrn.fsf@jogness.linutronix.de> MIME-Version: 1.0 List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "kexec" Errors-To: kexec-bounces+dwmw2=infradead.org@lists.infradead.org To: Petr Mladek Cc: Andrea Parri , Sergey Senozhatsky , Paul McKenney , Peter Zijlstra , Greg Kroah-Hartman , kexec@lists.infradead.org, linux-kernel@vger.kernel.org, Steven Rostedt , Sergey Senozhatsky , Thomas Gleixner , Linus Torvalds On 2020-06-25, Petr Mladek wrote: > On Thu 2020-06-18 16:55:19, John Ogness wrote: >> --- a/kernel/printk/printk.c >> +++ b/kernel/printk/printk.c >> @@ -1609,11 +1633,15 @@ int do_syslog(int type, char __user *buf, int len, int source) >> break; >> /* Number of chars in the log buffer */ >> case SYSLOG_ACTION_SIZE_UNREAD: >> + if (source != SYSLOG_FROM_PROC) { >> + text = kmalloc(LOG_LINE_MAX + PREFIX_MAX, GFP_KERNEL); >> + if (!text) >> + return -ENOMEM; > > The buffer is needed only to count lines to count the size of added > prefixes. Could we use the new prb_read_valid_info() that allows to > get the number of lines without actually reading the buffer? Yes! For the next version I introduce a macro to iterate just the meta data: #define prb_for_each_info(from, rb, s, i, lc) \ for ((s) = from; prb_read_valid_info(rb, s, i, lc); (s) = (i)->seq + 1) This can be used in all 3 locations where prb_count_lines() is used. In all three places, there is no need to be copying the data. And for SYSLOG_ACTION_SIZE_UNREAD, there is no need for the record and kmalloc'd buffer. This also means that prb_count_lines() will become a private static helper of the ringbuffer. John Ogness _______________________________________________ kexec mailing list kexec@lists.infradead.org http://lists.infradead.org/mailman/listinfo/kexec