From mboxrd@z Thu Jan 1 00:00:00 1970 From: "J. Bruce Fields" Subject: Re: [PATCH 6/9] sunrpc/cache: retry cache lookups that return -ETIMEDOUT Date: Mon, 1 Feb 2010 12:11:48 -0500 Message-ID: <20100201171148.GE15565@fieldses.org> References: <20090909062539.20462.67466.stgit@notabene.brown> <20090909063254.20462.41616.stgit@notabene.brown> <20091202221127.GB18690@fieldses.org> <20091203165729.GB1393@fieldses.org> <20091204153845.1ec83de5@notabene.brown> <20091205011742.GH22497@fieldses.org> <20091215172729.5e1d0190@notabene.brown> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: linux-nfs@vger.kernel.org To: Neil Brown Return-path: Received: from fieldses.org ([174.143.236.118]:58208 "EHLO fieldses.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751054Ab0BARLl (ORCPT ); Mon, 1 Feb 2010 12:11:41 -0500 In-Reply-To: <20091215172729.5e1d0190-wvvUuzkyo1EYVZTmpyfIwg@public.gmane.org> Sender: linux-nfs-owner@vger.kernel.org List-ID: On Tue, Dec 15, 2009 at 05:27:29PM +1100, Neil Brown wrote: > On Fri, 4 Dec 2009 20:17:42 -0500 > "J. Bruce Fields" wrote: > > > > > > > How about this as an alternate. I have only compile tested it, nothing more. > > > But if it looks good to you I'll make sure it really works. > > > > Well, without having really thinking about it: > > > > - If this were two separate patches, I'd have an easier time > > sorting out the interesting stuff from the trivial (though > > nevertheless good) hash-function reshuffling. > > I'll see what I can come up with... Have you had a chance to get back to this? > > > - Adding code to the common lookup_and_check() instead of to > > every caller certainly seems better, but too bad about the > > special cases that remain. > > yeah.... I could possibly add a pass-by-reference to lookup_and_check > which points to a possible cached value, but that would have > only one user, so the special case would be moved elsewhere... > ?? Yeah, that doesn't sound so great. > > - Something still seems odd here: we shouldn't ever have > > duplicate cache entries with the same key, because during > > their lifetimes cache entries are always kept in the hash. So > > why do we need extra code to check for that case? I may just > > be forgetting what we're doing here. Should I go reread the > > rest of the series? > > When sunrpc_update_cache is called to update and item that is > already valid, it unhashes that item and creates a new one. > (The unhashed item disappears once all the refcounts go). > So if we wait for user-space to update an entry for us, we > might find out that it has been unhashed, so we need to find > the new one. But nobody ever waits on a valid entry, right? So isn't the only case we care about the invalid case? I'll admit I haven't thought this through. --b.