From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.1 (2015-04-28) on archive.lwn.net X-Spam-Level: X-Spam-Status: No, score=-5.8 required=5.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,RCVD_IN_DNSWL_HI autolearn=ham autolearn_force=no version=3.4.1 Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by archive.lwn.net (Postfix) with ESMTP id CB9537D071 for ; Sat, 7 Jul 2018 03:02:27 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932470AbeGGDC0 (ORCPT ); Fri, 6 Jul 2018 23:02:26 -0400 Received: from mx3-rdu2.redhat.com ([66.187.233.73]:54736 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S932463AbeGGDC0 (ORCPT ); Fri, 6 Jul 2018 23:02:26 -0400 Received: from smtp.corp.redhat.com (int-mx06.intmail.prod.int.rdu2.redhat.com [10.11.54.6]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 788DE401EF27; Sat, 7 Jul 2018 03:02:25 +0000 (UTC) Received: from llong.remote.csb (ovpn-120-141.rdu2.redhat.com [10.10.120.141]) by smtp.corp.redhat.com (Postfix) with ESMTP id E51A7215688A; Sat, 7 Jul 2018 03:02:23 +0000 (UTC) Subject: Re: [PATCH v6 0/7] fs/dcache: Track & limit # of negative dentries To: Al Viro Cc: Jonathan Corbet , "Luis R. Rodriguez" , Kees Cook , linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, linux-doc@vger.kernel.org, Linus Torvalds , Jan Kara , "Paul E. McKenney" , Andrew Morton , Ingo Molnar , Miklos Szeredi , Matthew Wilcox , Larry Woodman , James Bottomley , "Wangkai (Kevin C)" References: <1530905572-817-1-git-send-email-longman@redhat.com> <20180706222814.GE30522@ZenIV.linux.org.uk> From: Waiman Long Organization: Red Hat Message-ID: <56b1d7ee-d362-f915-34fb-92173d512cbe@redhat.com> Date: Fri, 6 Jul 2018 23:02:23 -0400 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.2.0 MIME-Version: 1.0 In-Reply-To: <20180706222814.GE30522@ZenIV.linux.org.uk> Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit Content-Language: en-US X-Scanned-By: MIMEDefang 2.78 on 10.11.54.6 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.11.55.5]); Sat, 07 Jul 2018 03:02:25 +0000 (UTC) X-Greylist: inspected by milter-greylist-4.5.16 (mx1.redhat.com [10.11.55.5]); Sat, 07 Jul 2018 03:02:25 +0000 (UTC) for IP:'10.11.54.6' DOMAIN:'int-mx06.intmail.prod.int.rdu2.redhat.com' HELO:'smtp.corp.redhat.com' FROM:'longman@redhat.com' RCPT:'' Sender: linux-doc-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-doc@vger.kernel.org On 07/06/2018 06:28 PM, Al Viro wrote: > On Fri, Jul 06, 2018 at 03:32:45PM -0400, Waiman Long wrote: > >> With a 4.18 based kernel, the positive & negative dentries lookup rates >> (lookups per second) after initial boot on a 2-socket 24-core 48-thread >> 64GB memory system with and without the patch were as follows: ` >> >> Metric w/o patch neg_dentry_pc=0 neg_dentry_pc=1 >> ------ --------- --------------- --------------- >> Positive dentry lookup 584299 586749 582670 >> Negative dentry lookup 1422204 1439994 1438440 >> Negative dentry creation 643535 652194 641841 >> >> For the lookup rate, there isn't any signifcant difference with or >> without the patch or with a zero or non-zero value of neg_dentry_pc. > Sigh... What I *still* don't see (after all the iterations of the patchset) > is any performance data on workloads that would be likely to feel the impact. > Anything that seriously hits INCLUDE_PATH, for starters... I wrote a simple microbenchmark that does a lot of open() system calls to create positive or negative dentries. I was not seeing any noticeable performance difference as long as not too many negative dentries were created. Please enlighten me on how kind of performance benchmark that you would like me to run. Thanks, Longman -- To unsubscribe from this list: send the line "unsubscribe linux-doc" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html