From mboxrd@z Thu Jan 1 00:00:00 1970 From: George Beshers Subject: Re: iozone reality check: was zam, please discuss this Date: Wed, 23 Jun 2004 14:03:33 -0400 Message-ID: <40D9C5F5.7010605@comcast.net> References: <40D8EB0D.6050109@namesys.com> <20040623063049.GA5080@backtop.namesys.com> <40DA58BC.1060203@namesys.com> Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Return-path: list-help: list-unsubscribe: list-post: Errors-To: flx@namesys.com In-Reply-To: <40DA58BC.1060203@namesys.com> List-Id: Content-Type: text/plain; charset="us-ascii"; format="flowed" To: Hans Reiser Cc: ReiserFS List Caveat: I have not looked at the iozone test so this is purely in response to Han's description. The examples I know of are apps that allocate an mmap'd area for garbage collection: ocaml, sml-nj, and I believe ghc (Haskell) do this. While these systems usually have generational GCs at some point major collections happen and then I *believe* that you will see lots of dirty pages. Note: the 'believe' is based on some experiments on an SGI ccNuma system with profiling tools---I was looking at local access issues and noticed the pattern of changes to flag objects as "marked" in a mark/sweep collector. I then tried ocaml as an experiment and saw something similar. I have not look at Boehm conservative collector in some time, but if memory serves me correctly it uses separate arrays to hold the bits; using mmap is an option---I don't know if it is in common use. Some 18-20 months ago I spent some time looking at the Java GC but I don't remember its using mmap() and I no longer have the source available. George Beshers Hans Reiser wrote: > Alex Zarochentsev wrote: > >> On Tue, Jun 22, 2004 at 07:29:33PM -0700, Hans Reiser wrote: >> >> >>> http://www.namesys.com/intbenchmarks/mongo/04.05.04/256MB.RAM/comparison/smart-8k.noENTD.vs.ENTD/comp-ENTD.vs.noENTD.html >>> >>> >> >> >> Because direct page reclaiming (when a thread which needs memory does >> try_to_relase_page() by itself) is better then indirect one (through >> ENTD or whatever page reclaiming daemon). It is why Linux uses direct >> page reclaiming not indirect. >> >> >> > I apologize to zam, I meant to only cc this to reiserfs-dev. > I think this performance loss can be overcome, and needs to be > overcome so we can eliminate emergency flush and get good iozone > results. I should note though that Andrew Morton thinks iozone is a > benchmark that does things that no application does (dirtying massive > amounts of mmap'd pages). I am curious as to whether the sysadmins on > the list would agree with that (Andrew may be right).... >