linux-ext4 - Re: [PATCH] mke2fs: Disallow bigalloc with with bs

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Message-ID: <alpine.LFD.2.00.1304031645010.10110@localhost>
Date:	Wed, 3 Apr 2013 16:47:55 +0200 (CEST)
From:	Lukáš Czerner <lczerner@...hat.com>
To:	"Theodore Ts'o" <tytso@....edu>
cc:	Lukas Czerner <lczerner@...hat.com>, linux-ext4@...r.kernel.org
Subject: Re: [PATCH] mke2fs: Disallow bigalloc with with bs < 4096

On Wed, 3 Apr 2013, Theodore Ts'o wrote:

> Date: Wed, 3 Apr 2013 10:35:54 -0400
> From: Theodore Ts'o <tytso@....edu>
> To: Lukas Czerner <lczerner@...hat.com>
> Cc: linux-ext4@...r.kernel.org
> Subject: Re: [PATCH] mke2fs: Disallow bigalloc with with bs < 4096
> 
> On Wed, Apr 03, 2013 at 03:51:39PM +0200, Lukas Czerner wrote:
> > Currently there is nothing preventing user to create file system with
> > bigalloc feature enabled and block size smaller than 4096 Bytes. However
> > such combination does not make much sense at all because the whole point
> > of bigalloc is to have bigger allocation units.
> > 
> > This patch disallow such combination.
> 
> This makes sense by default but I do see a point in allowing it for
> testing purposes --- specifically, it allows us to verify that
> bigalloc works on architectures such as PowerPC and Itanium where page
> size is greater than the 4k block size.  So maybe a developer mode set
> via mke2fs.conf?

Yes, I though about that and I wanted to know what the general
opinion is. I'll prepare the patch which makes this tunable,
but restricted by default.

> 
> Another option would be to enforce that we only support bigalloc file
> systems where the blocksize == pagesize, but that means we wouldn't be
> able to mount 4k bigalloc file systems on architectures with a 8k or
> 16k page size.

Unfortunately we can't do that for the reasons you mentioned.

Thanks!
-Lukas

> 
> 						- Ted
> 
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