From: Lukas Czerner Subject: [PATCH 0/3] Lazy itable initialization for Ext4 Date: Fri, 20 Aug 2010 19:51:41 +0200 Message-ID: <1282326704-14838-1-git-send-email-lczerner@redhat.com> Cc: rwheeler@redhat.com, sandeen@redhat.com, jack@suse.cz, tytso@mit.edu, adilger@dilger.ca, lczerner@redhat.com To: linux-ext4@vger.kernel.org Return-path: Received: from mx1.redhat.com ([209.132.183.28]:57598 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752277Ab0HTRwF (ORCPT ); Fri, 20 Aug 2010 13:52:05 -0400 Sender: linux-ext4-owner@vger.kernel.org List-ID: Hi, all I am presenting you initial version of my lazy inode table initialization code for Ext4. The patch set consist of three patches. The first one adds helper function for blkdev_issue_zeroout called sb_issue_zeroout as I am using it to zero out inode table. Second patch adds new pair of mount options (inititable/noinititable), so you can enable or disable this feature. In default it is off (noinititable), so in order to try the new code you should moutn the fs like this: mount -o noinititable /dev/sda /mnt/ And finally the third patch adds the inode table initialization code itself. Thread initialization was heavily inspired by nilfs2 segctord. DESCRIPTION: When file system is mounted with "inititable" mount option, new thread (called itableinitd) is created. This thread walks through allocation groups searching for the group with not yet initialized inode table. When such a group is found it write zeroes through whole inode table and put itself into sleep for defined number of seconds to not disturb other ongoing I/O. This is repeated until it walks through every allocation group then the itableinitd thread is stopped. When regular inode allocation are going too fast, there is a chance that it hits the group with uninitialized inode table sooner than the itableinitd thread. In that case it just initializes the itable for itself the same way that itableinitd thread would do eventually. To prevent race conditions, each group is protected by the mutex. For now, there is no way to control itableinitd thread. It would probably be nice to have more control over how often it is woken up maybe through sysfs interface, or we can add some more logic into it in order to be more I/O sensitive and not put too much stress on already stressed system. However, this may be counterproductive, because we want inode table to be initialized before regular inode allocator hits it. Personally I think, we should create some kind of sysfs interface (/sys/fs/ext4//itable_init_interval ?) so the user space can watch the system and control itableinitd wake-up interval for itself. This is the first version of patch set and it received very limited testing so far. In order to try this patch you should do the following (aside compiling kernel with this patch) 1. Make Ext4 fs with lazy_itable_init extended option. mke2fs -T ext4 -E lazy_itable_init=1 2. Mount this file system with inititable mount option mount -o inititable Any comments are more than welcomed. Thanks! -Lukas --- [PATCH 1/3] Add helper function for blkdev_issue_zeroout [PATCH 2/3] Add inititable/noinititable mount options for ext4 [PATCH 3/3] Add inode table initialization code into Ext4 fs/ext4/ext4.h | 66 ++++++++++++ fs/ext4/ialloc.c | 75 +++++++++++++ fs/ext4/super.c | 274 ++++++++++++++++++++++++++++++++++++++++++++++++ include/linux/blkdev.h | 8 ++ 4 files changed, 423 insertions(+), 0 deletions(-)