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

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Date:	Wed, 2 Oct 2013 17:57:02 +0200
From:	Jan Kara <jack@...e.cz>
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 02-10-13 11:31:01, Benjamin LaHaise wrote:
> 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.
  Yes, but if we disable orlov allocation by clearing TOPDIR flag, we will
allocate inodes sequentially from the group which is what you want.

> 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().
  So i_mutex isn't held during fsync in ext4 in recent kernels. So that
won't be a source of contention anymore. But other directory operations
will be so I guess splitting files among lots of directories still makes
sence.

								Honza
-- 
Jan Kara <jack@...e.cz>
SUSE Labs, CR
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