linux-kernel - Re: Linux page cache issue?

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Date:	Mon, 2 Apr 2007 14:51:24 +0200
From:	Jan Kara <jack@...e.cz>
To:	Xin Zhao <uszhaoxin@...il.com>
Cc:	Dave Kleikamp <shaggy@...ux.vnet.ibm.com>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	linux-fsdevel <linux-fsdevel@...r.kernel.org>
Subject: Re: Linux page cache issue?

  Hi Xin,

On Thu 29-03-07 10:41:01, Xin Zhao wrote:
> I know we can use device inode's radix tree to achieve the same goal.
> The only downside could be: First, by default, Linux will not add the
> data pages into that radix tree. Only when a file is opened in
  Right.

> O_DIRECT, the data pages will be put into dev's radix tree. Moreover,
  If you use O_DIRECT, I don't think the data will and in any radix tree -
ideally they go directly to disk in this case.

> if the partition is big, I am not sure whether the lookup overhead is
> an issue. So it might need some optimization.
  Maybe, but I'd not say so as my first guess.

> Can you elaborate more about the aliasing issues mentioned in your
> email? I do have some mechanisms to handle the following situation:
> suppose two files share same data blocks. Now two processes open the
> two files separately. If one process writes a file, the other file
> will be affected. Is this the aliasing issue you referred to?
  Yes, this is exactly what I meant. Note that these problems are not
only about writes but also about truncate and such...

								Honza
-- 
Jan Kara <jack@...e.cz>
SuSE CR Labs
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