Before throwing the 'FUD' acronym around, maybe you should re-read the details. My point was that there were few users of cachefs even when the technology had the potential for greater benefit (slower networks, less powerful servers, smaller memory caches). Obviously cachefs can improve performance--it's simply a function of workload and the assumptions made about server/disk/network bandwidth. However, I would expect the real benefits and real beneficiaries to be fewer than in the past. HOWEVER^2 I did provide some argument(s) in favor of adding cachefs, and look forward to extensions to support delayed write, offline operation, and NFSv4 support with real consistency checking (as long as I don't have to take the customer calls ;-). BTW, animation/video shops were one group that did benefit, and I imagine they still could today (the one I had in mind did work across Britain, the US, and Asia and relied on cachefs for overcoming slow network connections). Wonder if the same company is a RH customer... All the comparisons to HTTP browser implementations are, imho, absurd. It's fine to keep a bunch of http data around on disk because a) it's RO data, b) correctness is not terribly important, and c) a human is generally the consumer and can manually request non-cached data if things look wonky. It is a trivial case of caching. As for security, look at what MIT had to do to prevent local disk caching from breaking the security guarantees of AFS. Customers (deluded or otherwise) are still customers. No one is forced to compile it into their kernel. Ship it. -Dan -----Original Message----- From: Trond Myklebust [mailto:trond.myklebust@xxxxxxxxxx] Sent: Monday, December 29, 2008 6:31 AM To: Andrew Morton Cc: Stephen Rothwell; Bernd Schubert; nfsv4@xxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx; steved@xxxxxxxxxx; dhowells@xxxxxxxxxx; linux-next@xxxxxxxxxxxxxxx; linux-fsdevel@xxxxxxxxxxxxxxx; rwheeler@xxxxxxxxxx Subject: Re: Pull request for FS-Cache, including NFS patches On Sun, 2008-12-28 at 20:01 -0800, Andrew Morton wrote: > On Mon, 29 Dec 2008 14:45:33 +1100 Stephen Rothwell <sfr@xxxxxxxxxxxxxxxx> wrote: > > > Hi David, > > > > On Fri, 19 Dec 2008 11:05:39 +1100 Stephen Rothwell <sfr@xxxxxxxxxxxxxxxx> wrote: > > > > > > Given the ongoing discussions around FS-Cache, I have removed it > > > from linux-next. Please ask me to include it again (if sensible) > > > once some decision has been reached about its future. > > > > What was the result of discussions around FS-Cache? > > There was none. > > Dan Muntz's question: > > Solaris has had CacheFS since ~1995, HPUX had a port of it since > ~1997. I'd be interested in evidence of even a small fraction of > Solaris and/or HPUX shops using CacheFS. I am aware of customers who > thought it sounded like a good idea, but ended up ditching it for > various reasons (e.g., CacheFS just adds overhead if you almost > always hit your local mem cache). > > was an very very good one. > > Seems that instead of answering it, we've decided to investigate the > fate of those who do not learn from history. David has given you plenty of arguments for why it helps scale the server (including specific workloads), has given you numbers validating his claim, and has presented claims that Red Hat has customers using cachefs in RHEL-5. The arguments I've seen against it, have so far been: 1. Solaris couldn't sell their implementation 2. It's too big 3. It's intrusive Argument (1) has so far appeared to be pure FUD. In order to discuss the lessons of history, you need to first do the work of analysing and understanding it first. I really don't see how it is relevant to Linux whether or not the Solaris and HPUX cachefs implementations worked out unless you can demonstrate that that their experience shows some fatal flaw in the arguments and numbers that David presented, and that his customers are deluded. If you want examples of permanent caches that clearly do help servers scale, then look no further than the on-disk caches used in almost all http browser implemantations. Alternatively, as David mentioned, there are the on-disk caches used by AFS/DFS/coda. (2) may be valid, but I have yet to see specifics for where you'd like to see the cachefs code slimmed down. Did I miss them? (3) was certainly true 3 years ago, when the code was first presented for review, and so we did a review and critique then. The NFS specific changes have improved greatly as a result, and as far as I know, the security folks are happy too. If you're not happy with the parts that affect the memory management code then, again, it would be useful to see specifics that what you want changed. If there is still controversy concerning this, then I can temporarily remove cachefs from the nfs linux-next branch, but I'm definitely keeping it in the linux-mm branch until someone gives me a reason for why it shouldn't be merged in its current state. Trond _______________________________________________ NFSv4 mailing list NFSv4@xxxxxxxxxxxxx http://linux-nfs.org/cgi-bin/mailman/listinfo/nfsv4 -- To unsubscribe from this list: send the line "unsubscribe linux-next" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
