From: Jan Kara <jack@suse.cz>
To: Theodore Ts'o <tytso@mit.edu>
Cc: Ext4 Developers List <linux-ext4@vger.kernel.org>
Subject: Re: [PATCH 00/12] jbd2 optimization and bug fixes
Date: Mon, 11 Feb 2013 16:52:59 +0100 [thread overview]
Message-ID: <20130211155259.GF5318@quack.suse.cz> (raw)
In-Reply-To: <1360446832-12724-1-git-send-email-tytso@mit.edu>
On Sat 09-02-13 16:53:40, Ted Tso wrote:
> I've been recently looking at journalling code in ext4, and it's clear
> that no one has really been through this code in a while. It's easy to
> find some easy optimization.
>
> Some general rules of thumb that developers should keep in mind when
> making changes to ext4:
>
> 1) It's important to minimize the amount of time that a handle is held
> active, since a journal commit can't be closed until all handles have
> been stopped. In the ideal world, disk reads and memory allocations
> should be done *before* calling ext4_journal_start().
>
> 2) It's important that number of credits needed for a particular handle
> be large enough; otherwise it's possible that we run out of space in the
> journal without being able to finish the handle.
>
> 3) It's also important that we not overestimate then number of credits
> needed, since otherwise we might close a transaction too early --- and
> in particular, the process which starts the transaction commit process
> will tend to suffer the greatest amount of latency.
True but it's not too bad - we give back the credits we didn't use once
the current handle is dropped. But if there are many handles open in
parallel or if the overestimate is really huge, it will have visible
effects. So I agree it's good to keep the estimate as close as resonably
possible to reality.
> Currently enabling quotas cause the number of credits required to
> balloon significantly. Most of the time we need nowhere the number of
> credits which we reserve, so there's opportunity to optimize things.
> (For example, we could make sure create the quota record is created in a
> seprate transaction.)
So write(2) and similar calls are already optimized. You are right that
create(2) or unlink(2) still overestimate needed credits only due to
remotely possible worst case.
Honza
--
Jan Kara <jack@suse.cz>
SUSE Labs, CR
prev parent reply other threads:[~2013-02-11 15:53 UTC|newest]
Thread overview: 34+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-02-09 21:53 [PATCH 00/12] jbd2 optimization and bug fixes Theodore Ts'o
2013-02-09 21:53 ` [PATCH 01/12] jbd2: track request delay statistics Theodore Ts'o
2013-02-11 15:57 ` Jan Kara
2013-02-09 21:53 ` [PATCH 02/12] jbd2: revert "jbd2: add COW fields to struct jbd2_journal_handle" Theodore Ts'o
2013-02-11 15:58 ` Jan Kara
2013-02-09 21:53 ` [PATCH 03/12] jbd2: add tracepoints which provide per-handle statistics Theodore Ts'o
2013-02-09 21:53 ` [PATCH 04/12] ext4: move the jbd2 wrapper functions out of super.c Theodore Ts'o
2013-02-09 21:53 ` [PATCH 05/12] ext4: pass context information to jbd2__journal_start() Theodore Ts'o
2013-02-11 16:16 ` Jan Kara
2013-02-11 18:13 ` Theodore Ts'o
2013-02-11 19:58 ` Jan Kara
2013-02-11 20:14 ` Theodore Ts'o
2013-02-09 21:53 ` [PATCH 06/12] ext4: grab page before starting transaction handle in write_begin() Theodore Ts'o
2013-02-11 16:35 ` Jan Kara
2013-02-09 21:53 ` [PATCH 07/12] ext4: start handle at the last possible moment in ext4_unlink() Theodore Ts'o
2013-02-11 16:21 ` Jan Kara
2013-02-09 21:53 ` [PATCH 08/12] ext4: start handle at the last possible moment in ext4_rmdir() Theodore Ts'o
2013-02-11 16:22 ` Jan Kara
2013-02-09 21:53 ` [PATCH 09/12] ext4: fix the number of credits needed for ext4_ext_migrate() Theodore Ts'o
2013-02-11 16:26 ` Jan Kara
2013-02-09 21:53 ` [PATCH 10/12] ext4: fix the number of credits needed for ext4_unlink() and ext4_rmdir() Theodore Ts'o
2013-02-11 16:28 ` Jan Kara
2013-02-11 18:30 ` Theodore Ts'o
2013-02-11 19:30 ` Jan Kara
2013-02-09 21:53 ` [PATCH 11/12] ext4: fix the number of credits needed for acl ops with inline data Theodore Ts'o
2013-02-10 13:42 ` Tao Ma
2013-02-10 18:15 ` Shentino
2013-02-10 19:43 ` Theodore Ts'o
2013-02-11 16:16 ` Andreas Dilger
2013-02-11 16:30 ` Jan Kara
2013-02-09 21:53 ` [PATCH 12/12] ext4: start handle at the last possible moment when creating inodes Theodore Ts'o
2013-02-11 1:47 ` Theodore Ts'o
2013-02-11 16:00 ` Andreas Dilger
2013-02-11 15:52 ` Jan Kara [this message]
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