linux-kernel - Re: [PATCH] [ARM] force dcache flush if dcache

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Date:	Mon, 12 Oct 2009 22:42:22 +0530
From:	Nitin Gupta <ngupta@...are.org>
To:	Hugh Dickins <hugh.dickins@...cali.co.uk>,
	David Miller <davem@...emloft.net>,
	Nick Piggin <npiggin@...e.de>,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
	linux-arch@...r.kernel.org
Subject: Re: [PATCH] [ARM] force dcache flush if dcache_dirty bit set

On 10/12/2009 10:33 PM, Russell King wrote:
> On Mon, Oct 12, 2009 at 05:09:53PM +0100, Hugh Dickins wrote:
>> Sorry to muddy the waters on this, if you and Dave are sure that
>> you have the right fix, down in your architectures, and that fix
>> isn't going to hurt your performance significantly.
> 
> If I look at the issue from this point of view:
> 
> - we are using PG_arch_1 to delay cache handling for the page
> 
> - if PG_arch_1 is set on a page, we set it explicitly because we
>   didn't do some flushing between the allocation of the page and
>   mapping it into userspace
> 
> - if a page with PG_arch_1 set ever gets to userspace, this can
>   only be because we did the lazy flushing thing
>

 
> I don't see that there should have been any bearing on whether a page
> has a mapping or not when we get to update_mmu_cache.  The issue here
> is that > if PG_arch_1 is set on a page, then we didn't flush it at
> the time when we believed it was appropriate to do so. <
> 


Presented so clearly by Russell and this is exactly what I meant, though
the example just focused on some particular swap case which I happen to
stumble upon while working on something similar.

Thanks,
Nitin
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