Date: Fri, 11 May 2007 10:27:39 +0100 (BST)
From: Hugh Dickins <hugh@veritas.com>
To: Andrew Morton <akpm@linux-foundation.org>
cc: Andi Kleen <ak@suse.de>, William Lee Irwin III <wli@holomorphy.com>,
       Linus Torvalds <torvalds@linux-foundation.org>,
       Christoph Lameter <clameter@sgi.com>,
       David Miller <davem@davemloft.net>, linux-kernel@vger.kernel.org
Subject: Re: slub-i386-support.patch
In-Reply-To: <20070511004200.6d30152e.akpm@linux-foundation.org>
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On Fri, 11 May 2007, Andrew Morton wrote:
> On Fri, 11 May 2007 10:29:30 +0200 Andi Kleen <ak@suse.de> wrote:
> 
> > > I'm guessing (haven't rechecked source) that the cpu_idle() call comes
> > > about because the top level pgd of a process gets freed very late in
> > > its exit, and after a great flurry of processes have just exited,
> > > perhaps there was nothing to free up the accumulation.  Though
> > > it still strikes me as an odd place to do it.
> > 
> > I always found it odd and probably the wrong place too.
> 
> so... what's the bottom line here, guys?  Should we change that patch?

The bottom line... I can see why you're asking for that ;)

I'd say delete the change to arch/i386/kernel/smp.c - contrary to
what Christoph says, no other arch buries a check_pgt_cache() call
in flush_tlb_mm(), that just seems to be a thinko: i386 has the usual
call to it from tlb_finish_mmu() - _that_ is the one which he and
David were talking about.

I'm just worried that there might somewhere be a call to flush_tlb_mm()
which would now be surprised to be freeing pages: almost certainly not,
but why raise that concern?  It's just not flush_tlb_mm()'s business.

The cpu_idle() call should stay for now: we're agreed that it's odd,
but there's plenty of precedent for it, and it's easier to imagine it
serves a real purpose, and shouldn't be removed without replacement.

Bill raised a real concern about unnecessary PAE pgd memory usage,
but let's get the patch into -rc1 to enable the wider SLUB testing,
before coming back to fix that up.  His micro-optimizations can wait.

IMHO
Hugh
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