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=-0.9 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS 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 45C6FC3F2CF for ; Fri, 28 Feb 2020 04:53:03 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 11139246A2 for ; Fri, 28 Feb 2020 04:53:03 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=themaw.net header.i=@themaw.net header.b="GZOcs8xD"; dkim=pass (2048-bit key) header.d=messagingengine.com header.i=@messagingengine.com header.b="qbgmEM9m" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1725802AbgB1ExC (ORCPT ); Thu, 27 Feb 2020 23:53:02 -0500 Received: from new1-smtp.messagingengine.com ([66.111.4.221]:41605 "EHLO new1-smtp.messagingengine.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725730AbgB1ExC (ORCPT ); Thu, 27 Feb 2020 23:53:02 -0500 Received: from compute2.internal (compute2.nyi.internal [10.202.2.42]) by mailnew.nyi.internal (Postfix) with ESMTP id 9186E5E3E; Thu, 27 Feb 2020 23:53:01 -0500 (EST) Received: from mailfrontend2 ([10.202.2.163]) by compute2.internal (MEProxy); Thu, 27 Feb 2020 23:53:01 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=themaw.net; h= message-id:subject:from:to:cc:date:in-reply-to:references :content-type:mime-version:content-transfer-encoding; s=fm2; bh= QaGDiOWBjcbn4rDNlKqOONKkTcLMMhgcigudu4fkTbM=; b=GZOcs8xDttkrjAVH NW9UlrkQHXPo/yp+iwzXrgXI2kwoirhgmPKFo2IiP93xmQIntQbvsTBtJfRWbUk6 hS2XBceoGb1Lf0EWHXoc1SALBi0oDKpu46k4ZWx5hWeXuEAt3KonSJHOFgHPwX6U t9qHrh42MNfipoF/IjTo9N4zoHql4Nz11N2kcyFih9JkEOJuuuVrPdzffd8JwDyb mow3W9mqXvX57e/4DbRq3j7gnKySA92lowvBWNGa8lAeWvDgb1UJQEn+3o7DiOd9 n7MOlLGe0q1ZIqnKowyLEe6RDoe1iRqED+P4jXHGiAM6PTxYPHY7XHulnBsu6Tpy mTMlWw== DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d= messagingengine.com; h=cc:content-transfer-encoding:content-type :date:from:in-reply-to:message-id:mime-version:references :subject:to:x-me-proxy:x-me-proxy:x-me-sender:x-me-sender :x-sasl-enc; s=fm2; bh=QaGDiOWBjcbn4rDNlKqOONKkTcLMMhgcigudu4fkT bM=; b=qbgmEM9mb8vbUI3ZVYzTO8aH27yRXZWIPIyOebMpXlXWzQDXqEwEIIiRI 3HuNvlmmLpNhM2h8ab/H4PvyxdIRPojyG40qxhJVmxruoQ8eUXvbr73nFSzFJ/ZS 3E3cVQ7e33DvkJkyIDKoQAhx60sTmw2S53kHQ+6Uh0p5To9c8FxU3GkrPUi3L0fc 98+segKQUKNehg+9skkC53roy7m4vN46zx6baUGxXSAkvio4vKp58l2iYpbe3QZs iLb++WKJX5Ffb8aQqYjLvIa0DtD/w61BQTL3p0PoOIwYbZ/3QYngqMzcNqYr57yC n69weE2/LZUy6ZS5jMv57C//FG3gw== X-ME-Sender: X-ME-Proxy-Cause: gggruggvucftvghtrhhoucdtuddrgedugedrleejgdejkecutefuodetggdotefrodftvf curfhrohhfihhlvgemucfhrghsthforghilhdpqfgfvfdpuffrtefokffrpgfnqfghnecu uegrihhlohhuthemuceftddtnecusecvtfgvtghiphhivghnthhsucdlqddutddtmdenuc fjughrpefkuffhvfffjghftggfggfgsehtjeertddtreejnecuhfhrohhmpefkrghnucfm vghnthcuoehrrghvvghnsehthhgvmhgrfidrnhgvtheqnecukfhppeduudekrddvtdelrd dukedvrdeludenucevlhhushhtvghrufhiiigvpedtnecurfgrrhgrmhepmhgrihhlfhhr ohhmpehrrghvvghnsehthhgvmhgrfidrnhgvth X-ME-Proxy: Received: from mickey.themaw.net (unknown [118.209.182.91]) by mail.messagingengine.com (Postfix) with ESMTPA id ED8323060D1A; Thu, 27 Feb 2020 23:52:55 -0500 (EST) Message-ID: <2b03788f9d71d9d972cbe908e0f0fb0e37672719.camel@themaw.net> Subject: Re: [PATCH 00/11] fs/dcache: Limit # of negative dentries From: Ian Kent To: Al Viro , Matthew Wilcox Cc: Andreas Dilger , Waiman Long , Jonathan Corbet , Luis Chamberlain , Kees Cook , Iurii Zaikin , Linux Kernel Mailing List , Linux FS Devel , linux-doc@vger.kernel.org, Mauro Carvalho Chehab , Eric Biggers , Dave Chinner , Eric Sandeen Date: Fri, 28 Feb 2020 12:52:52 +0800 In-Reply-To: <20200228042208.GI23230@ZenIV.linux.org.uk> References: <20200226161404.14136-1-longman@redhat.com> <20200226162954.GC24185@bombadil.infradead.org> <2EDB6FFC-C649-4C80-999B-945678F5CE87@dilger.ca> <9d7b76c32d09492137a253e692624856388693db.camel@themaw.net> <20200228033412.GD29971@bombadil.infradead.org> <20200228042208.GI23230@ZenIV.linux.org.uk> Content-Type: text/plain; charset="UTF-8" User-Agent: Evolution 3.32.5 (3.32.5-1.fc30) MIME-Version: 1.0 Content-Transfer-Encoding: 7bit Sender: linux-doc-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-doc@vger.kernel.org On Fri, 2020-02-28 at 04:22 +0000, Al Viro wrote: > On Thu, Feb 27, 2020 at 07:34:12PM -0800, Matthew Wilcox wrote: > > On Thu, Feb 27, 2020 at 05:55:43PM +0800, Ian Kent wrote: > > > Not all file systems even produce negative hashed dentries. > > > > > > The most beneficial use of them is to improve performance of > > > rapid > > > fire lookups for non-existent names. Longer lived negative hashed > > > dentries don't give much benefit at all unless they suddenly have > > > lots of hits and that would cost a single allocation on the first > > > lookup if the dentry ttl expired and the dentry discarded. > > > > > > A ttl (say jiffies) set at appropriate times could be a better > > > choice all round, no sysctl values at all. > > > > The canonical argument in favour of negative dentries is to improve > > application startup time as every application searches the library > > path > > for the same libraries. Only they don't do that any more: > > Tell that to scripts that keep looking through $PATH for > binaries each time they are run. Tell that to cc(1) looking through > include path, etc. > > Ian, autofs is deeply pathological in that respect; that's OK, > since it has very unusual needs, but please don't use it as a model > for anything else - its needs *are* unusual. Ok, but my thoughts aren't based on autofs behaviours. But it sounds like you don't believe this is a sensible suggestion and you would know best so ... Ian