netdev - Re: [PATCH 1/2] af_packet: use vmalloc_to_page() instead for the addresss returned by vmalloc()

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Date:	Wed, 01 Dec 2010 14:38:11 +0100
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Changli Gao <xiaosuo@...il.com>
Cc:	Neil Horman <nhorman@...driver.com>,
	"David S. Miller" <davem@...emloft.net>,
	Jiri Pirko <jpirko@...hat.com>, netdev@...r.kernel.org
Subject: Re: [PATCH 1/2] af_packet: use vmalloc_to_page() instead for the
 addresss returned by vmalloc()

Le mercredi 01 décembre 2010 à 21:05 +0800, Changli Gao a écrit :
> On Tue, Nov 30, 2010 at 10:37 PM, Neil Horman <nhorman@...driver.com> wrote:
> > Off the top of my head, I would think that pgv_to_page could be prototyped such
> > that it could accept addr, offset and struct page ** arguments.  That way we can
> > track the current page that we're mapped to, lowering the number of calls to
> > vmalloc_to_page, and we can still use an increment like we do above (as long as
> > its wrapped in a subsequent call to pgv_to_page)
> 
> I'll try to optimize pgv_to_page() after this patch series merged. I
> am planning to call vmalloc_to_page() previously, and cache its result
> in a per pgv array for future use. Thanks.
> 
> 

Hmm... fact is flush_dcache_page() is void on some arches.

Maybe the only thing to do is avoid pgv_to_page() calls if
ARCH_IMPLEMENTS_FLUSH_DCACHE_PAGE is 0

    The ARCH_IMPLEMENTS_FLUSH_DCACHE_PAGE symbol was introduced to avoid
    pointless empty cache-thrashing loops on architectures for which
    flush_dcache_page() is a no-op.  Every architecture was provided with this
    flush pages on architectires where ARCH_IMPLEMENTS_FLUSH_DCACHE_PAGE is
    equal 1 or do nothing otherwise.



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