From: Theodore Ts'o Subject: [PATCH 52/52] ext4: Documention update for new ordered mode and delayed allocation Date: Sat, 5 Jul 2008 13:36:18 -0400 Message-ID: <1215279378-30504-53-git-send-email-tytso@mit.edu> References: <1215279378-30504-1-git-send-email-tytso@mit.edu> <1215279378-30504-2-git-send-email-tytso@mit.edu> <1215279378-30504-3-git-send-email-tytso@mit.edu> <1215279378-30504-4-git-send-email-tytso@mit.edu> <1215279378-30504-5-git-send-email-tytso@mit.edu> <1215279378-30504-6-git-send-email-tytso@mit.edu> <1215279378-30504-7-git-send-email-tytso@mit.edu> <1215279378-30504-8-git-send-email-tytso@mit.edu> <1215279378-30504-9-git-send-email-tytso@mit.edu> <1215279378-30504-10-git-send-email-tytso@mit.edu> <1215279378-30504-11-git-send-email-tytso@mit.edu> <1215279378-30504-12-git-send-email-tytso@mit.edu> <1215279378-30504-13-git-send-email-tytso@mit.edu> <1215279378-30504-14-git-send-email-tytso@mit.edu> <1215279378-30504-15-git-send-email-tytso@mit.edu> <1215279378-30504-16-git-send-email-tytso@mit.edu> <1215279378-30504-17-git-send-email-tytso@mit.edu> <1215279378-30504-18-git-send-email-tytso@mit.edu> <1215279378-30504-19-git-send-email-tytso@mit.edu> <1215279378-30504-20-git-send-email-tytso@mit.edu> <1215279378-30504-21-git-send-email-tytso@mit.edu> <1215279378-30504-22-git-send-email-tytso@mit.edu> <1215279378-30504-23-git-send-email-tytso@mit.edu> <1215279378-30504-24-git-send-email-tytso@mit.edu> <1215279378-30504-25-git-send-email-tytso@mit.edu> <1215279378-30504-26-git-send-email-tytso@mit.edu> <1215279378-30504-27-git-send-email-tytso@mit.edu> <1215279378-30504-28-git-send-email-tytso@mit.edu> <1215279378-30504-29-git-send-email-tytso@mit.edu> <1215279378-30504-30-git-send-email-tytso@mit.edu> <1215279378-30504-31-git-send-email-tytso@mit.edu> <1215279378-30504-32-git-send-email-tytso@mit.edu> <1215279378-30504-33-git-send-email-tytso@mit.edu> <1215279378-30504-34-git-send-email-tytso@mit.edu> <1215279378-30504-35-git-send-email-tytso@mit.edu> <1215279378-30504-36-git-send-email-tytso@mit.edu> <1215279378-30504-37-git-send-email-tytso@mit.edu> <1215279378-30504-38-git-send-email-tytso@mit.edu> <1215279378-30504-39-git-send-email-tytso@mit.edu> <1215279378-30504-40-git-send-email-tytso@mit.edu> <1215279378-30504-41-git-send-email-tytso@mit.edu> <1215279378-30504-42-git-send-email-tytso@mit.edu> <1215279378-30504-43-git-send-email-tytso@mit.edu> <1215279378-30504-44-git-send-email-tytso@mit.edu> <1215279378-30504-45-git-send-email-tytso@mit.edu> <1215279378-30504-46-git-send-email-tytso@mit.edu> <1215279378-30504-47-git-send-email-tytso@mit.edu> <1215279378-30504-48-git-send-email-tytso@mit.edu> <1215279378-30504-49-git-send-email-tytso@mit.edu> <1215279378-30504-50-git-send-email-tytso@mit.edu> <1215279378-30504-51-git-send-email-tytso@mit.edu> <1215279378-30504-52-git-send-email-tytso@mit.edu> Cc: Mingming Cao , "Theodore Ts'o" To: Ext4 Developers List , Linux Kernel Developers List Return-path: Received: from www.church-of-our-saviour.ORG ([69.25.196.31]:33027 "EHLO thunker.thunk.org" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1754322AbYGERg3 (ORCPT ); Sat, 5 Jul 2008 13:36:29 -0400 In-Reply-To: <1215279378-30504-52-git-send-email-tytso@mit.edu> Sender: linux-ext4-owner@vger.kernel.org List-ID: From: Mingming Cao Adding some documentations for delayed allocation and new ordered mode. Signed-off-by: Mingming Cao Signed-off-by: "Theodore Ts'o" --- Documentation/filesystems/ext4.txt | 21 ++++++++++++++------- 1 files changed, 14 insertions(+), 7 deletions(-) diff --git a/Documentation/filesystems/ext4.txt b/Documentation/filesystems/ext4.txt index 77ed8fe..e2afb6e 100644 --- a/Documentation/filesystems/ext4.txt +++ b/Documentation/filesystems/ext4.txt @@ -62,7 +62,7 @@ Mailing list: linux-ext4@vger.kernel.org * extent format reduces metadata overhead (RAM, IO for access, transactions) * extent format more robust in face of on-disk corruption due to magics, * internal redunancy in tree -* improved file allocation (multi-block alloc, delayed alloc) +* improved file allocation (multi-block alloc) * fix 32000 subdirectory limit * nsec timestamps for mtime, atime, ctime, create time * inode version field on disk (NFSv4, Lustre) @@ -73,6 +73,10 @@ Mailing list: linux-ext4@vger.kernel.org flex_bg feature * large file support * Inode allocation using large virtual block groups via flex_bg +* delayed allocation +* large block (up to pagesize) support +* efficent new ordered mode in JBD2 and ext4(avoid using buffer head to force + the ordering) 2.2 Candidate features for future inclusion @@ -235,7 +239,9 @@ stripe=n Number of filesystem blocks that mballoc will try to use for allocation size and alignment. For RAID5/6 systems this should be the number of data disks * RAID chunk size in file system blocks. - +delalloc (*) Deferring block allocation until write-out time. +nodelalloc Disable delayed allocation. Blocks are allocation + when data is copied from user to page cache. Data Mode ========= There are 3 different data modes: @@ -249,10 +255,10 @@ typically provide the best ext4 performance. * ordered mode In data=ordered mode, ext4 only officially journals metadata, but it logically -groups metadata and data blocks into a single unit called a transaction. When -it's time to write the new metadata out to disk, the associated data blocks -are written first. In general, this mode performs slightly slower than -writeback but significantly faster than journal mode. +groups metadata information related to data changes with the data blocks into a +single unit called a transaction. When it's time to write the new metadata +out to disk, the associated data blocks are written first. In general, +this mode performs slightly slower than writeback but significantly faster than journal mode. * journal mode data=journal mode provides full data and metadata journaling. All new data is @@ -260,7 +266,8 @@ written to the journal first, and then to its final location. In the event of a crash, the journal can be replayed, bringing both data and metadata into a consistent state. This mode is the slowest except when data needs to be read from and written to disk at the same time where it -outperforms all others modes. +outperforms all others modes. Curently ext4 does not have delayed +allocation support if this data journalling mode is selected. References ========== -- 1.5.6.rc3.1.g36b7.dirty