linux-kernel - Re: [PATCH v3 0/2] fadvise: support POSIX_FADV

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Date:	Tue, 12 Jul 2011 17:36:01 -0700
From:	"Patrick J. LoPresti" <lopresti@...il.com>
To:	Andrea Righi <andrea@...terlinux.com>
Cc:	linux-kernel@...r.kernel.org, akpm@...ux-foundation.org
Subject: Re: [PATCH v3 0/2] fadvise: support POSIX_FADV_NOREUSE

On Tue, Jul 12, 2011 at 3:22 PM, Andrea Righi <andrea@...terlinux.com> wrote:
>
> If the file data is not in memory you can't set a bit in any struct
> page. You could even open a file and execute POSIX_FADV_NOREUSE without
> reading any page from the file.

Mmm, too bad.

> I think it would be better to maintain a list of file offset/length
> structures per file descriptor or (as a starting solution) even mark the
> entire file as non-cacheable without considering the ranges.

I recommend against the "whole file" approach.  In my application (for
instance), I deal with files in the hundreds of gigabytes.  Marking
the whole file non-cacheable, when I was just trying to give a hint
about a few hundred megs, would be a total disaster.

I would suggest implementing it right or leaving it as a no-op.  Just my $0.02.

Thanks for working on this.  Better support for these page cache hints
will be great to see.

 - Pat
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