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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id BEFC9C433EF for ; Tue, 21 Jun 2022 02:10:46 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S245676AbiFUCKp convert rfc822-to-8bit (ORCPT ); Mon, 20 Jun 2022 22:10:45 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:38764 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S242831AbiFUCKn (ORCPT ); Mon, 20 Jun 2022 22:10:43 -0400 Received: from relay4.hostedemail.com (smtprelay0017.hostedemail.com [216.40.44.17]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 4AF2E1EC62 for ; Mon, 20 Jun 2022 19:10:42 -0700 (PDT) Received: from omf14.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay01.hostedemail.com (Postfix) with ESMTP id C4A4C61081; Tue, 21 Jun 2022 02:10:40 +0000 (UTC) Received: from [HIDDEN] (Authenticated sender: joe@perches.com) by omf14.hostedemail.com (Postfix) with ESMTPA id F267A32; Tue, 21 Jun 2022 02:10:38 +0000 (UTC) Message-ID: Subject: Re: [PATCH v4 00/34] Printbufs - new data structure for building strings From: Joe Perches To: Kent Overstreet , Andrew Morton Cc: David Laight , "linux-kernel@vger.kernel.org" , "linux-mm@kvack.org" , "pmladek@suse.com" , "rostedt@goodmis.org" , "enozhatsky@chromium.org" , "linux@rasmusvillemoes.dk" , "willy@infradead.org" , Miguel Ojeda Date: Mon, 20 Jun 2022 19:10:38 -0700 In-Reply-To: References: <20220620004233.3805-1-kent.overstreet@gmail.com> <0a5901f8460f452a89c9b0cda32fb833@AcuMS.aculab.com> <20220620150514.3tjy5dv7pv5frcwd@moria.home.lan> <53d77ae6101a0f24cfb694174d4c7699424c57e8.camel@perches.com> <20220621005752.ohiq5besmy3r5rjo@moria.home.lan> Content-Type: text/plain; charset="ISO-8859-1" Content-Transfer-Encoding: 8BIT User-Agent: Evolution 3.44.1-0ubuntu1 MIME-Version: 1.0 X-Rspamd-Queue-Id: F267A32 X-Stat-Signature: ddwoawxpcobobp4d4tcbgu83yqtpn9bi X-Rspamd-Server: rspamout01 X-Session-Marker: 6A6F6540706572636865732E636F6D X-Session-ID: U2FsdGVkX18Xz7rjAxOO7jXBkzbfuwKRIweIFY8sohA= X-HE-Tag: 1655777438-450937 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, 2022-06-20 at 18:26 -0700, Joe Perches wrote: > On Mon, 2022-06-20 at 20:57 -0400, Kent Overstreet wrote: > > On Mon, Jun 20, 2022 at 05:38:51PM -0700, Joe Perches wrote: > > > On Mon, 2022-06-20 at 11:07 -0400, Kent Overstreet wrote: > > > > On Mon, Jun 20, 2022 at 04:19:31AM +0000, David Laight wrote: > > > > > I really think that is a bad idea. > > > > > printk() already uses a lot of stack, anything doing a recursive > > > > > call is just making that worse. > > > > > Especially since these calls can often be in error paths > > > > > which are not often tested and can already be on deep stacks. > > > > > > > > We went over this before - this patch series drastically reduces stack usage of > > > > sprintf by eliminating a bunch of stack allocated buffers. Do try to keep up... > > > > > > I generally agree with David. > > > > > > I think Kent has not provided data that this actually _reduces_ > > > stack usage. > > > > I think the people who are comfortable with reading C can discern that when > > large stack allocated character arrays are deleted, frame size and stack usage > > go down. > > I am very comfortable reading C. > > You have not provided any data. In a brief looking around at stack uses in vsprintf, I believe this is the largest stack declaration there. Especially since KSYM_NAME_LEN was increased to 512 by commit 394dffa6680c ("kallsyms: increase maximum kernel symbol length to 512") Perhaps this stack declaration should instead be an alloc/free as it can be quite large. I suppose one could quibble about the kzalloc vs kmalloc or the nominally unnecessary initialization of sym. I think this makes sense though and it reduces the #ifdef uses too. --- lib/vsprintf.c | 41 ++++++++++++++++++++++++----------------- 1 file changed, 24 insertions(+), 17 deletions(-) diff --git a/lib/vsprintf.c b/lib/vsprintf.c index c414a8d9f1ea9..30113a30fd88a 100644 --- a/lib/vsprintf.c +++ b/lib/vsprintf.c @@ -980,30 +980,37 @@ char *symbol_string(char *buf, char *end, void *ptr, struct printf_spec spec, const char *fmt) { unsigned long value; -#ifdef CONFIG_KALLSYMS - char sym[KSYM_SYMBOL_LEN]; -#endif + char *sym = NULL; if (fmt[1] == 'R') ptr = __builtin_extract_return_addr(ptr); value = (unsigned long)ptr; -#ifdef CONFIG_KALLSYMS - if (*fmt == 'B' && fmt[1] == 'b') - sprint_backtrace_build_id(sym, value); - else if (*fmt == 'B') - sprint_backtrace(sym, value); - else if (*fmt == 'S' && (fmt[1] == 'b' || (fmt[1] == 'R' && fmt[2] == 'b'))) - sprint_symbol_build_id(sym, value); - else if (*fmt != 's') - sprint_symbol(sym, value); - else - sprint_symbol_no_offset(sym, value); + if (IS_ENABLED(CONFIG_KALLSYMS) && + (sym = kzalloc(KSYM_SYMBOL_LEN, GFP_NOWAIT | __GFP_NOWARN))) { + char *rtn; + + if (*fmt == 'B' && fmt[1] == 'b') + sprint_backtrace_build_id(sym, value); + else if (*fmt == 'B') + sprint_backtrace(sym, value); + else if (*fmt == 'S' && + (fmt[1] == 'b' || + (fmt[1] == 'R' && fmt[2] == 'b'))) + sprint_symbol_build_id(sym, value); + else if (*fmt != 's') + sprint_symbol(sym, value); + else + sprint_symbol_no_offset(sym, value); + + rtn = string_nocheck(buf, end, sym, spec); + + kfree(sym); + + return rtn; + } - return string_nocheck(buf, end, sym, spec); -#else return special_hex_number(buf, end, value, sizeof(void *)); -#endif } static const struct printf_spec default_str_spec = {