From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754082AbdEXRkE (ORCPT ); Wed, 24 May 2017 13:40:04 -0400 Received: from bombadil.infradead.org ([65.50.211.133]:35372 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753880AbdEXRkB (ORCPT ); Wed, 24 May 2017 13:40:01 -0400 Date: Wed, 24 May 2017 10:40:00 -0700 From: Christoph Hellwig To: Shaohua Li Cc: Christoph Hellwig , linux-kernel@vger.kernel.org, tj@kernel.org, gregkh@linuxfoundation.org, viro@zeniv.linux.org.uk, Kernel-team@fb.com Subject: Re: [PATCH 1/5] kernfs: implement i_generation Message-ID: <20170524174000.GC13151@infradead.org> References: <1840aeeff2e745d223b01514a433b4b7f20040a6.1495490800.git.shli@fb.com> <20170523074112.GD29525@infradead.org> <20170523150946.GA6123@smirco-mbp.DHCP.thefacebook.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20170523150946.GA6123@smirco-mbp.DHCP.thefacebook.com> User-Agent: Mutt/1.8.0 (2017-02-23) X-SRS-Rewrite: SMTP reverse-path rewritten from by bombadil.infradead.org. See http://www.infradead.org/rpr.html Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, May 23, 2017 at 08:09:48AM -0700, Shaohua Li wrote: > > > diff --git a/fs/kernfs/dir.c b/fs/kernfs/dir.c > > > index db5900aaa..09d093e 100644 > > > --- a/fs/kernfs/dir.c > > > +++ b/fs/kernfs/dir.c > > > @@ -634,6 +634,7 @@ static struct kernfs_node *__kernfs_new_node(struct kernfs_root *root, > > > if (ret < 0) > > > goto err_out2; > > > kn->ino = ret; > > > + kn->generation = atomic_inc_return(&root->next_generation); > > > > i_generation is only supposed to be valid on a per-inode basis, so this > > global counter seems really odd. > > What's the difference between per-inode or per-super? The i_generation doesn't > need to be consecutive for an inode. I checked other fs, a lot of filesystems > implement i_generation in this way, for example, f2fs, ext4. of course per-sb is a valid implementation, but it seems like introducing an easily avoidable bottleneck by serializing on a per-sb cacheline for each file creation. But then again it seems like kernfs already has various other per-sb contention points, so maybe it's not an issue in the end.