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Date: Thu, 7 Feb 2002 04:48:14 -0500
From: Benjamin LaHaise <bcrl@redhat.com>
To: Andrew Morton <akpm@zip.com.au>
Cc: "David S. Miller" <davem@redhat.com>, hugh@veritas.com,
        marcelo@conectiva.com.br, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] __free_pages_ok oops
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In-Reply-To: <3C621C74.8A005EB6@zip.com.au>; from akpm@zip.com.au on Wed, Feb 06, 2002 at 10:19:32PM -0800
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On Wed, Feb 06, 2002 at 10:19:32PM -0800, Andrew Morton wrote:
> It's only a problem if this is the final put_page().  In the
> case of sendfile(), process-context code can be taught to take
> a temporary reference on the page, and only release it after the network
> stack is known to have finished with the page. sendfile is synchronous, yes?
> 
> And in the case of all other skb frees, the underlying page
> won't be on the LRU.  I hope.

sendfile isn't synchronous, nor is aio, which also relies on freeing pages 
acquired from user mappings in irq/bh/whatever context.  Restricting where 
pages may be freed really ties our hands on what is possible for zero copy 
io. (ie O_DIRECT, aio, sendfile, TUX all get hosed by this).

		-ben (who is really on vacation)
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