From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from zape.um.es (localhost [127.0.0.1]) by zape.um.es (8.9.1b+Sun/8.9.1) with ESMTP id OAA00565 for ; Sun, 9 Dec 2001 14:03:49 +0100 (MET) Date: Sun, 9 Dec 2001 13:58:50 +0100 (CET) From: Juan Piernas Canovas Subject: Re: ext3 writeback mode slower than ordered mode? In-Reply-To: <3C12C57C.FF93FAC0@zip.com.au> Message-ID: MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: owner-linux-mm@kvack.org Return-Path: To: Andrew Morton Cc: zlatko.calusic@iskon.hr, sct@redhat.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org List-ID: On Sat, 8 Dec 2001, Andrew Morton wrote: > Zlatko Calusic wrote: > > > > Hi! > > > > My apologies if this is an FAQ, and I'm still catching up with > > the linux-kernel list. > > > > Today I decided to convert my /tmp partition to be mounted in > > writeback mode, as I noticed that ext3 in ordered mode syncs every 5 > > seconds and that is something defenitely not needed for /tmp, IMHO. > > > > Then I did some tests in order to prove my theory. :) > > > > But, alas, writeback is slower. > > > > I cannot reproduce this. Using http://www.zip.com.au/~akpm/writer.c > > ext2: 0.03s user 1.43s system 97% cpu 1.501 total > ext3 writeback: 0.02s user 2.33s system 96% cpu 2.431 total > ext3 ordered: 0.02s user 2.52s system 98% cpu 2.574 total > > ext3 is significantly more costly in either journalling mode, > probably because of the bitmap manipulation - each time we allocate > a block to the file, we have to muck around doing all sorts > of checks and list manipulations against the buffer which holds > the bitmap. Not only is this costly, but ext2 speculatively > sets a bunch of bits at the same time, which ext3 cannot do > for consistency reasons. > > There are a few things we can do to pull this back, but given that > this is all pretty insignificant once you actually start doing disk > IO, we couldn't justify the risk of destabilising the filesystem > for small gains. Hi! Sorry, but I can confirm that Ext3 is slower with "-o data=writeback" option than with "-o data=ordered" option when you create and delete a lot of files. I use 2.2.19 Linux kernel along with 0.0.7a Ext3 version. Bye! Juan. -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/