linux-kernel - Re: [Devel] Re: [PATCH 2.6.19-rc3] VFS: per-sb dentry lru list

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Date:	Tue, 14 Nov 2006 15:51:08 +1100
From:	Neil Brown <neilb@...e.de>
To:	Kirill Korotaev <dev@...ru>
Cc:	devel@...nvz.org, Vasily Averin <vvs@...ru>,
	Andrew Morton <akpm@...l.org>,
	Kirill Korotaev <dev@...nvz.org>,
	Balbir Singh <balbir@...ibm.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	David Howells <dhowells@...hat.com>, Olaf Hering <olh@...e.de>,
	Jan Blunck <jblunck@...e.de>
Subject: Re: [Devel] Re: [PATCH 2.6.19-rc3] VFS: per-sb dentry lru list

On Wednesday November 1, dev@...ru wrote:
> <<<< AFAICS, doing so you introduced a leak of anonymous dentries.
> 
> d_alloc_anon() calls d_alloc() with parent == NULL, i.e. dentries have no parent
> and are not linked to the sb->s_root...

Yep, thanks.

> BTW, looking at it, I found that s_anon field on super block is not
> used any more. 

I don't know what you mean by that.  It is still used...

> we can add BUG_ON(!hlist_empty(&sb->s_anon)) in generic_shutdown_super to avoid such issues like this.
> 
> maybe we can fix it adding something like:
> while (!list_empty(&sb->s_anon)))
>     prune_dcache(MAX_INT, &sb->s_anon);

It seems that anon dentries can now have children (I think someone
explained that too me - shrink_dcache_for_umount certainly suggests
it).
Also, in this context we cannot be sure that all dentries can be
freed.  This is being called a remount time remember, and some stuff
might still be in use.

We probably need to move the s_anon list to a temporary list and
repeatedly:
  move the top entry back to s_anon and call shrink_dcache_parent
 on it.

Needs more thought.
	
NeilBrown
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