linux-ext4 - Re: [PATCH] Remove ext4 xattr mbcache to fix CPU lockup when using ceph #107301

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Date:	Fri, 20 Nov 2015 23:22:08 -0500
From:	Theodore Ts'o <tytso@....edu>
To:	Andreas Dilger <adilger@...ger.ca>
Cc:	Laurent GUERBY <laurent@...rby.net>, Jan Kara <jack@...e.cz>,
	"linux-ext4@...r.kernel.org" <linux-ext4@...r.kernel.org>,
	"sage@...hat.com" <sage@...hat.com>,
	Abaakouk Mehdi <sileht@...eht.net>,
	Loic Dachary <loic@...hary.org>
Subject: Re: [PATCH] Remove ext4 xattr mbcache to fix CPU lockup when using
 ceph #107301

On Fri, Nov 20, 2015 at 06:08:15PM -0700, Andreas Dilger wrote:
> 
> I'm definitely not in favor of deleting mbcache entirely, just having the
> mount option to disable it in cases where it is known not to be useful,
> such as Ceph or Lustre backing stores that never have shared xattrs.
> 
> In some cases mbcache can be useful, since it allows sharing xattrs
> between inodes. 
> 
> I thought you would update our patch to add the mount option to disable
> mbcache?

And better yet would be if there was a blacklist of Lustre and Ceph
xattr type/keys that will never have shared attrs, so that mbcache is
not used for those xattrs automatically, *without* using a mount
option.  Can someone at least start help creating that list?

But yeah, a complete deletion of mbcache is a non-starter.

Regards,

						- Ted
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