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Date: Thu, 15 Jun 2006 08:40:34 +0800
From: Fengguang Wu <fengguang.wu@gmail.com>
To: Bernard Blackham <b-lkml@blackham.com.au>
Cc: linux-kernel@vger.kernel.org, Lubos Lunak <l.lunak@suse.cz>,
       Dirk Mueller <dmueller@suse.de>, Badari Pulavarty <pbadari@us.ibm.com>,
       Andrew Morton <akpm@osdl.org>
Subject: Re: [RFC] the /proc/filecache interface
Message-ID: <20060615004034.GA5013@mail.ustc.edu.cn>
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	Bernard Blackham <b-lkml@blackham.com.au>,
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Hi Bernard,

On Wed, Jun 14, 2006 at 11:38:37PM +0800, Bernard Blackham wrote:
> I haven't been following this closely, so I apologise if I'm out of
> my depth. It would be a useful add-on to be able to use this
> interface to force something _out_ of the page cache also. For
> example, for performance tests, or selectively ditching pages before
> software suspending.

Sure we can add more related commands into it.

For example, the functions in fs/drop_caches.c are well suited for
this interface. The current sysctl interface is a quick hacking:

/* A global variable is a bit ugly, but it keeps the code simple */
int sysctl_drop_caches;

The following scheme may be more reasonable:

# echo -n "drop files" > /proc/filecache
# echo -n "drop slabs" > /proc/filecache

As for the "selectively ditching pages" function, my original scheme
is to
        - query /proc/filecache to answer the question of "which pages
          are cached, and their status(referenced/active etc.)"
        - run "fadvise filename page-offset pages" to ditch pages
Do you think it as convenient?

Thanks,
Wu