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 4ED5FC41513 for ; Fri, 4 Aug 2023 11:47:42 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230205AbjHDLrl (ORCPT ); Fri, 4 Aug 2023 07:47:41 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:46326 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229679AbjHDLrj (ORCPT ); Fri, 4 Aug 2023 07:47:39 -0400 Received: from out30-112.freemail.mail.aliyun.com (out30-112.freemail.mail.aliyun.com [115.124.30.112]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id A7784180; Fri, 4 Aug 2023 04:47:16 -0700 (PDT) X-Alimail-AntiSpam: AC=PASS;BC=-1|-1;BR=01201311R111e4;CH=green;DM=||false|;DS=||;FP=0|-1|-1|-1|0|-1|-1|-1;HT=ay29a033018046059;MF=xueshuai@linux.alibaba.com;NM=1;PH=DS;RN=16;SR=0;TI=SMTPD_---0Vp0KRY2_1691149631; Received: from 30.240.114.112(mailfrom:xueshuai@linux.alibaba.com fp:SMTPD_---0Vp0KRY2_1691149631) by smtp.aliyun-inc.com; Fri, 04 Aug 2023 19:47:13 +0800 Message-ID: Date: Fri, 4 Aug 2023 19:47:09 +0800 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.15; rv:102.0) Gecko/20100101 Thunderbird/102.13.1 Subject: Re: [PATCH v4 2/2] perf record: Update docs regarding the maximum limitation of AUX area Content-Language: en-US To: Leo Yan , James Clark Cc: alexander.shishkin@linux.intel.com, peterz@infradead.org, mingo@redhat.com, baolin.wang@linux.alibaba.com, acme@kernel.org, mark.rutland@arm.com, jolsa@kernel.org, namhyung@kernel.org, irogers@google.com, adrian.hunter@intel.com, linux-perf-users@vger.kernel.org, linux-kernel@vger.kernel.org, nathan@kernel.org, bpf@vger.kernel.org References: <20230804072945.85731-1-xueshuai@linux.alibaba.com> <20230804072945.85731-3-xueshuai@linux.alibaba.com> <20230804084643.GA589820@leoy-yangtze.lan> From: Shuai Xue In-Reply-To: <20230804084643.GA589820@leoy-yangtze.lan> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2023/8/4 16:46, Leo Yan wrote: > On Fri, Aug 04, 2023 at 03:29:45PM +0800, Shuai Xue wrote: >> The maximum AUX area is limited by the page size of the system. Update >> the documentation to reflect this. >> >> Signed-off-by: Shuai Xue >> --- >> tools/perf/Documentation/perf-record.txt | 3 +++ >> 1 file changed, 3 insertions(+) >> >> diff --git a/tools/perf/Documentation/perf-record.txt b/tools/perf/Documentation/perf-record.txt >> index 680396c56bd1..b0ee7b63da0e 100644 >> --- a/tools/perf/Documentation/perf-record.txt >> +++ b/tools/perf/Documentation/perf-record.txt >> @@ -292,6 +292,9 @@ OPTIONS >> Also, by adding a comma, the number of mmap pages for AUX >> area tracing can be specified. >> >> + The maximum AUX area is limited by the page size of the system. For >> + example with 4K pages configured, the maximum is 2GiB. >> + > > This statement is incorrect as it fails to give out prerequisites. > > E.g., on Arm64, for 4KiB, 16KiB or 64KiB base page size, different page > size has different default values for MAX_ORDER. Furthermore, MAX_ORDER > can be set by config ARCH_FORCE_MAX_ORDER, thus we cannot arbitrarily > say the maximum allocation size is 2GiB for 4KiB page size. > Hi, Leo, You are right, thank you for point this out. Maybe we could consider to use a formula to present the avaliable > maximum buffer size: > > PAGE_SIZE << MAX_ORDER > ( ---------------------- ) * PAGE_SIZE > sizeof(page_pointer) > > PAGE_SIZE << MAX_ORDER : the size of maximal physically > contiguous allocations, which is the maximum size can be > allocated by slab/slub. I agree that a formula to present that limitation is more accurate. But as @James commented in last v3, "Minor nit: I wouldn't expect a Perf tool user to know what "MAX_ORDER" is", how about to keep both: The maximum AUX area is limited by the maximum physically contiguous memory allocated from slab/slub. It can be calculated with following formula: PAGE_SIZE << MAX_ORDER ( ---------------------- ) * PAGE_SIZE sizeof(page_pointer) For example with 4K pages and MAX_ORDER=10 configured, the maximum AUX area is 2GiB. Thank you. Best Regards, Shuai