linux-ext4 - Re: [PATCH] ext4: add noorlov parameter to avoid spreading of directory inodes

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Date:	Wed, 2 Oct 2013 18:44:56 +0200 (CEST)
From:	Lukáš Czerner <lczerner@...hat.com>
To:	Benjamin LaHaise <bcrl@...ck.org>
cc:	Eric Sandeen <sandeen@...hat.com>, Jan Kara <jack@...e.cz>,
	"Theodore Ts'o" <tytso@....edu>,
	Andreas Dilger <adilger.kernel@...ger.ca>,
	linux-ext4@...r.kernel.org
Subject: Re: [PATCH] ext4: add noorlov parameter to avoid spreading of
 directory inodes

On Wed, 2 Oct 2013, Benjamin LaHaise wrote:

> Date: Wed, 2 Oct 2013 11:31:01 -0400
> From: Benjamin LaHaise <bcrl@...ck.org>
> To: Eric Sandeen <sandeen@...hat.com>
> Cc: Jan Kara <jack@...e.cz>, Theodore Ts'o <tytso@....edu>,
>     Andreas Dilger <adilger.kernel@...ger.ca>, linux-ext4@...r.kernel.org
> Subject: Re: [PATCH] ext4: add noorlov parameter to avoid spreading of
>     directory inodes
> 
> On Wed, Oct 02, 2013 at 10:02:12AM -0500, Eric Sandeen wrote:
> > I'm right with you on thinking a mount option should be a last resort.
> > 
> > One thing I'm curious about - what changed from ext3 to ext4?  I thought
> > both defaulted to orlov and the same type of allocation behavior, more
> > or less.  I guess one change is that the "oldalloc" mount
> > option went away.
> 
> > (if it does come back, it should probably mirror what we had before,
> > which was "oldalloc" not "noorlov" right?)
> 
> The behaviour I'm looking for is not exactly the same as the orlov
> allocator or the old allocator, but something that packs files as
> closely together as possible.  Half of this can be achieved with
> fallocate(), but reducing the spreading of directory inodes can only be
> accomplished with changes to the filesystem itself.  The only reason
> we're using multiple subdirectories is because of contention issues with
> i_mutex (our application has to either fsync() the directory or mount
> with dirsync to maintain consistency) during file creation and unlink().

What is the frequency of unlink operation in comparison to file
creation ? There is a possible issue with the global goal cursors
s_mb_last_group and s_mb_last_start which might make your files
increasingly scattered across the disk. I've attempted to address
this problem with my patch

ext4: Try to better reuse recently freed space

What is the usual size of the files this application is creating ?

Thanks!
-Lukas

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