Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753882AbbDPUmM (ORCPT ); Thu, 16 Apr 2015 16:42:12 -0400 Received: from mail-ig0-f175.google.com ([209.85.213.175]:34771 "EHLO mail-ig0-f175.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752770AbbDPUmF (ORCPT ); Thu, 16 Apr 2015 16:42:05 -0400 Message-ID: <1429216923.7346.211.camel@edumazet-glaptop2.roam.corp.google.com> Subject: Re: [RFC PATCH] fs: use a sequence counter instead of file_lock in fd_install From: Eric Dumazet To: Al Viro Cc: Mateusz Guzik , Andrew Morton , "Paul E. McKenney" , Yann Droneaud , Konstantin Khlebnikov , linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org Date: Thu, 16 Apr 2015 13:42:03 -0700 In-Reply-To: <20150416180932.GW889@ZenIV.linux.org.uk> References: <20150416121628.GA20615@mguzik> <20150416180932.GW889@ZenIV.linux.org.uk> Content-Type: text/plain; charset="UTF-8" X-Mailer: Evolution 3.10.4-0ubuntu2 Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1162 Lines: 28 On Thu, 2015-04-16 at 19:09 +0100, Al Viro wrote: > On Thu, Apr 16, 2015 at 02:16:31PM +0200, Mateusz Guzik wrote: > > @@ -165,8 +165,10 @@ static int expand_fdtable(struct files_struct *files, int nr) > > cur_fdt = files_fdtable(files); > > if (nr >= cur_fdt->max_fds) { > > /* Continue as planned */ > > + write_seqcount_begin(&files->fdt_seqcount); > > copy_fdtable(new_fdt, cur_fdt); > > rcu_assign_pointer(files->fdt, new_fdt); > > + write_seqcount_end(&files->fdt_seqcount); > > if (cur_fdt != &files->fdtab) > > call_rcu(&cur_fdt->rcu, free_fdtable_rcu); > > Interesting. AFAICS, your test doesn't step anywhere near that path, > does it? So basically you never hit the retries during that... Right, but then the table is almost never changed for a given process, as we only increase it by power of two steps. (So I scratch my initial comment, fdt_seqcount is really mostly read) -- 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/