Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932903AbbENLXs (ORCPT ); Thu, 14 May 2015 07:23:48 -0400 Received: from ipmail07.adl2.internode.on.net ([150.101.137.131]:39819 "EHLO ipmail07.adl2.internode.on.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752912AbbENLXo (ORCPT ); Thu, 14 May 2015 07:23:44 -0400 X-IronPort-Anti-Spam-Filtered: true X-IronPort-Anti-Spam-Result: A2A8CABxhVRV//DOLHlcgw9UXrJmAQEBAQEBBplKAgIBAQKBOU0BAQEBAQGBC4QiAQEBAwEnExwjBQsIAxgJJQ8FJQMhE4gkB9UzAQEIAgEfGIV+hSSFBQeELQWdUZZ6I2GDKCwxgkYBAQE Date: Thu, 14 May 2015 21:23:04 +1000 From: Dave Chinner To: Linus Torvalds Cc: Al Viro , Linux Kernel Mailing List , linux-fsdevel , Christoph Hellwig , Neil Brown Subject: Re: [RFC][PATCHSET v3] non-recursive pathname resolution & RCU symlinks Message-ID: <20150514112304.GT15721@dastard> References: <20150505052205.GS889@ZenIV.linux.org.uk> <20150511180650.GA4147@ZenIV.linux.org.uk> <20150513222533.GA24192@ZenIV.linux.org.uk> <20150514033040.GF7232@ZenIV.linux.org.uk> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2462 Lines: 56 On Wed, May 13, 2015 at 08:52:59PM -0700, Linus Torvalds wrote: > On Wed, May 13, 2015 at 8:30 PM, Al Viro wrote: > > > > Maybe... I'd like to see the profiles, TBH - especially getxattr() and > > access() frequency on various loads. Sure, make(1) and cc(1) really care > > about stat() very much, but I wouldn't be surprised if something like > > httpd or samba would be hitting getxattr() a lot... > > So I haven't seen samba profiles in ages, but iirc we have more > serious problems than trying to speed up basic filename lookup. > > At least long long ago, inode semaphore contention was a big deal, > largely due to readdir(). It still is - it's the prime reason people still need to create hashed directory structures so that they can get concurrency in directory operations. IMO, concurrency in directory operations is a more important problem to solve than worrying about readdir speed; in large filesystems readdir and lookup are IO bound operations and so everything serialises on the IO as it's done with the i_mutex held.... > And readdir() itself, for that matter - we have no good vfs-level > readdir caching, so it all ends up serialized on the inode > semaphore, and it all goes all the way into the filesystem to get > the readdir data. And at least for ext4, readdir() > is slow anyway, because it doesn't use the page cache, it uses > that good old buffer cache, because of how ext4 does metadata > journaling etc. IIRC, ext4 readdir is not slow because of the use of the buffer cache, it's slow because of the way it hashes dirents across blocks on disk. i.e. it has locality issues, not a caching problem. > Having readdir() caching at the VFS layer would likely be a really > good thing, but it's hard. It *might* be worth looking at the nfs4 > code to see if we could possibly move some of that code into the vfs > layer, but the answer is likely "no", or at least "that's incredibly > painful". Maybe I'm missing something - what operation would be sped up by caching readdir data? Are you trying to optimise the ->lookup that tends to follow readdir by caching individual dirents? Or something else? Cheers, Dave. -- Dave Chinner david@fromorbit.com -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/