linux-kernel - Re: [RFC PATCH] Implement slub fastpath with sequence number

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Date:	Tue, 11 Mar 2008 20:41:09 +1100
From:	Nick Piggin <nickpiggin@...oo.com.au>
To:	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>
Cc:	Christoph Lameter <clameter@....com>, linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH] Implement slub fastpath with sequence number

On Tuesday 11 March 2008 20:31, Mathieu Desnoyers wrote:
> Here is a new version that works. tested on x86. tweaked the bitmasks
> into unions to remove operations from the critical path, but I tried to
> keep that clean. It applies on vm.git HEAD.
>
> It allows the cmpxchg_local to detect object re-use by keeping a counter in
> the freeoffset MSBs.
>
> Whenever an object is freed in the cpu slab cache, the counter is
> incremented. Whenever the alloc/free slow paths are modifying the offset or
> freebase, the sequence counter is also incremented. It is used to make sure
> we know if freebase has been modified in an interrupt nested over the fast
> path.

Wow. I applaud the effort to micro optimise things ;)

But I hope this doesn't get merged until macro-regressions in SLUB
are verified to be fixed. It's pretty clear that SLUB's problem is
not fastpath performance, so I think this would be premature
optimisation.

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