From mboxrd@z Thu Jan 1 00:00:00 1970 From: Theodore Ts'o Subject: Re: [RFC] A proposal for adding case insensitive lookups to ext4 Date: Fri, 4 Nov 2016 20:00:52 -0400 Message-ID: <20161105000052.54dmfdp5sgiqq6wo@thunk.org> References: <20161103172842.q7avc7rztny3zndd@thunk.org> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: Ext4 Developers List , Daniel Rosenberg , guy@linux.com To: Jeremy Allison Return-path: Received: from imap.thunk.org ([74.207.234.97]:51024 "EHLO imap.thunk.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751497AbcKEAA5 (ORCPT ); Fri, 4 Nov 2016 20:00:57 -0400 Content-Disposition: inline In-Reply-To: Sender: linux-ext4-owner@vger.kernel.org List-ID: On Fri, Nov 04, 2016 at 04:28:05PM -0700, Jeremy Allison wrote: > I don't suppose ext4 has a negative cache for lookups ? That would > certainly help the linear search case on lookup miss. The dcache caches negative results, so as long as the lookup miss is for the same non-existing file name, that's not a problem. The issue will be if someone is using Makefile with default rules, say, and Makefile is checking for foo.y, foo.l, foo.C, etc. for each object file, there could be a fairly large number of failed lookups that might require O(n) lookups. Eventually all of these will be cached, yes, but it could be a large number of negative dentry caches. However, I'm not sure I care; no self-respecting programmer should be using a case-insensitive file system, so in practice, I'm not sure it matters all that much.... - Ted