linux-kernel - Re: SLUB defrag pull request?

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Message-Id: <E1KsluU-0002R1-Ow@pomaz-ex.szeredi.hu>
Date:	Thu, 23 Oct 2008 00:10:34 +0200
From:	Miklos Szeredi <miklos@...redi.hu>
To:	cl@...ux-foundation.org
CC:	miklos@...redi.hu, penberg@...helsinki.fi, 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, Christoph Lameter wrote:
> On Wed, 22 Oct 2008, Miklos Szeredi wrote:
> 
> >> 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.
> 
> Plus the allocator may be reusing parts of the freed object for a freelist 
> etc even if the object is not poisoned.

Actually, no: looking at the slub code it already makes sure that
objects are neither poisoned, nor touched in any way _if_ there is a
constructor for the object.  And for good reason too, otherwise a
reused object would contain rubbish after a second allocation.

Come on guys, you should be the experts in this thing!

So again, just checking d_lru should do work fine.  There's absolutely
no need to mess with extra references in a separate phase, which leads
to lots of complications.

Miklos
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