linux-ext4 - Re: [PATCH] ext4: fix online resize with mballoc

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Date:	Fri, 27 Jun 2008 17:54:28 -0600
From:	Andreas Dilger <adilger@....com>
To:	Frédéric Bohé <frederic.bohe@...l.net>
Cc:	linux-ext4@...r.kernel.org
Subject: Re: [PATCH] ext4: fix online resize with mballoc

On Jun 27, 2008  16:36 +0200, Frďż˝dďż˝ric Bohďż˝ wrote:
> Le jeudi 26 juin 2008 Ă  17:26 -0600, Andreas Dilger a ĂŠcrit :
> > On Jun 26, 2008  16:58 +0200, Frďż˝dďż˝ric Bohďż˝ wrote:
> > > From: Frederic Bohe <frederic.bohe@...l.net>
> > > +	num_meta_group_infos_max = num_meta_group_infos +
> > > +				le16_to_cpu(es->s_reserved_gdt_blocks);
> > 
> > The only drawback of NOT handling this properly is that once (eventually)
> > we allow resizing with META_BG this code will be broken again.  It at
> > least deserves a comment like "Need to handle this properly when META_BG
> > resizing is allowed" so that it will show up on any grep for META_BG.
> > 
> > It probably also makes sense to round this up to the next power-of-two
> > value, since kmalloc will do that internally anyways, and it gives us
> > some resizing headroom for no cost.
> 
> Do you have any idea of how this headroom could be used in the future ?

For e.g. resize with META_BG, which does not need new reserved blocks
to be added.  Since the space is already allocated because of kmalloc
use of 2^n slab size, we may as well make it "available" even if it isn't
used.

Cheers, Andreas
--
Andreas Dilger
Sr. Staff Engineer, Lustre Group
Sun Microsystems of Canada, Inc.

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