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Date: Wed, 25 Jan 2012 14:56:55 -0800
From: Julian Elischer <julian@freebsd.org>
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To: John Baldwin <jhb@freebsd.org>
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Cc: freebsd-current@freebsd.org, Tijl Coosemans <tijl@coosemans.org>
Subject: Re: posix_fadvise noreuse disables file caching
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On 1/25/12 8:29 AM, John Baldwin wrote:
>
> So I've came up with this untested patch.  It uses
> VOP_ADVISE(FADV_DONTNEED) after read(2) calls to a NOREUSE region, and
> leaves read-ahead caching enabled for NOREUSE.  FADV_DONTNEED doesn't
> do any good really for writes (it only flushes clean buffers), so I've
> left write(2) operations as using IO_DIRECT still.  Does this sound
> reasonable?

That sounds like a good solution. If people want something from write they
can do it separately. For what it's worth, I would expect NOREUSE on 
write to still do
write clustering but to free the buffer once it is written.