linux-ext4 - Re: [2.6 patch] FS_MBCACHE: don't needlessly make it built-in

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Message-ID: <48A8EA65.9090204@redhat.com>
Date:	Sun, 17 Aug 2008 22:20:05 -0500
From:	Eric Sandeen <sandeen@...hat.com>
To:	Andreas Dilger <adilger@....com>
CC:	Adrian Bunk <bunk@...nel.org>,
	Andreas Gruenbacher <agruen@...e.de>,
	linux-ext4@...r.kernel.org
Subject: Re: [2.6 patch] FS_MBCACHE: don't needlessly make it built-in

Andreas Dilger wrote:
> On Aug 03, 2008  21:43 +0300, Adrian Bunk wrote:
>> Assume you have:
>> - one or more of ext2/3/4 statically built into your kernel
>> - none of these with extended attributes enabled and
>> - want to add onother one of ext2/3/4 modular and with
>>   extended attributes enabled
>>
>> then you currently have to reboot to use it since this results in 
>> CONFIG_FS_MBCACHE=y.
>>
>> That's not a common issue, but I just ran into it and since there's no 
>> reason to get a built-in mbcache in this case this patch fixes it.
> 
> To be honest, I'd like an option to disable MBCACHE entirely.  This
> code is of no use if the EAs on an inode are not identical (i.e. if
> anything other than ACLs are in use)

or selinux....

> and is also not useful if the
> xattrs fit into the large inodes in ext4 (and ext3 if the filesystem
> is formatted with this option).

... which is now the default.

a config option sounds reasonable to me, too.  I think by the time EAs
spill out of the inode, the chance of them being identical is pretty
small?  (i.e. a single acl set, or selinux context may be common, but if
you have enough to not fit in the inode it's more likely to be a
mishmash of things?)

-Eric


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

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