linux-kernel - Re: SLUB defrag pull request?

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Message-Id: <E1Ksksa-0002Iq-EV@pomaz-ex.szeredi.hu>
Date:	Wed, 22 Oct 2008 23:04:32 +0200
From:	Miklos Szeredi <miklos@...redi.hu>
To:	penberg@...helsinki.fi
CC:	miklos@...redi.hu, cl@...ux-foundation.org,
	nickpiggin@...oo.com.au, hugh@...itas.com, linux-mm@...ck.org,
	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
	akpm@...ux-foundation.org
Subject: Re: SLUB defrag pull request?

On Wed, 22 Oct 2008, Pekka Enberg wrote:
> On Wed, Oct 22, 2008 at 11:26 PM, Miklos Szeredi <miklos@...redi.hu> wrote:
> > Because you don't _need_ a reliable reference to access the contents
> > of the dentry.  The dentry is still there after being freed, as long
> > as the underlying slab is there and isn't being reused for some other
> > purpose.  But you can easily ensure that from the slab code.
> >
> > Hmm?
> 
> Actually, when debugging is enabled, it's customary to poison the
> object, for example (see free_debug_processing() in mm/slub.c). So we
> really can't "easily ensure" that in the allocator unless we by-pass
> all the current debugging code.

Thank you, that does actually answer my question.  I would still think
it's a good sacrifice to no let the dentries be poisoned for the sake
of a simpler dentry defragmenter.

Miklos
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