Date: Fri, 26 Mar 2004 12:33:03 -0800
From: Andrew Morton <akpm@osdl.org>
To: davidm@hpl.hp.com
Cc: davidm@napali.hpl.hp.com, davej@redhat.com, mpm@selenic.com,
       linux-kernel@vger.kernel.org
Subject: Re: Fw: potential /dev/urandom scalability improvement
Message-Id: <20040326123303.7a775b02.akpm@osdl.org>
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David Mosberger <davidm@napali.hpl.hp.com> wrote:
>
> >>>>> On Fri, 26 Mar 2004 10:49:04 -0800, Andrew Morton <akpm@osdl.org> said:
> 
>   Andrew> But the start address which is fed into prefetch_range() may
>   Andrew> not be cacheline-aligned.  So if appropriately abused, a
>   Andrew> prefetch_range() could wander off the end of the user's
>   Andrew> buffer and into a new page.
> 
>   Andrew> I think this gets it right, but I probably screwed something
>   Andrew> up.
> 
> Please, let's not make this more complicated than it is.  The
> cacheline alignment doesn't matter at all.  Provided prefetch_range()
> is given a range of guaranteed to be valid memory, then it will be
> fine.  It never touches anything outside the specified range.

If someone does, say,

	prefetch_range(some_pointer, sizeof(*some_pointer));

then it is possible that prefetch_range() could

a) execute a prefetch at addresses which are not PREFETCH_STRIDE-aligned
   and, as a consequence,

b) prefetch data from the next page, outside the range of the user's
   (addr,len).

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