linux-kernel - Re: [patch 1/5] avoid tlb gather restarts.

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Message-Id: <1183534671.1208.22.camel@localhost>
Date:	Wed, 04 Jul 2007 09:37:51 +0200
From:	Martin Schwidefsky <schwidefsky@...ibm.com>
To:	Hugh Dickins <hugh@...itas.com>
Cc:	akpm@...ux-foundation.org, peterz@...radead.org,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [patch 1/5] avoid tlb gather restarts.

On Tue, 2007-07-03 at 18:42 +0100, Hugh Dickins wrote:
> > If need_resched() is false in the inner loop of unmap_vmas it is
> > unnecessary to do a full blown tlb_finish_mmu / tlb_gather_mmu for
> > each ZAP_BLOCK_SIZE ptes. Do a tlb_flush_mmu() instead. That gives
> > architectures with a non-generic tlb flush implementation room for
> > optimization. The tlb_flush_mmu primitive is a available with the
> > generic tlb flush code, the ia64_tlb_flush_mm needs to be renamed
> > and a dummy function is added to arm and arm26.
> > 
> > Signed-off-by: Martin Schwidefsky <schwidefsky@...ibm.com>
> 
> Acked-by: Hugh Dickins <hugh@...itas.com>
> 
> (Looking at it, I see that we could argue that there ought to be a
> need_resched() etc. check after your tlb_flush_mmu() in unmap_vmas,
> in case it's spent a long while in there on some arches; but I don't
> think we have the ZAP_BLOCK_SIZE tuned with any great precision, and
> you'd at worst be doubling the latency there, so let's not worry
> about it.  I write this merely in order to reserve myself an
> "I told you so" if anyone ever notices increased latency ;)

Hmm, we'd have to repeat the longish if statement to make sure we don't
miss a cond_resched after tlb_flush_mmu. I'd rather not do that.

-- 
blue skies,
  Martin.

"Reality continues to ruin my life." - Calvin.


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