From mboxrd@z Thu Jan  1 00:00:00 1970
From: Christoph Hellwig <hch@infradead.org>
Subject: Re: [RFC] VFS: File System Mount Wide O_DIRECT Support
Date: Tue, 4 Sep 2012 06:57:14 -0400
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To: Li Wang <liwang@nudt.edu.cn>
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On Tue, Sep 04, 2012 at 06:17:47PM +0800, Li Wang wrote:
> For file system created on file-backed loop device, there will be two-levels of 
> page cache present, which typically doubles the memory consumption. 

And the right fix is to not use buffer I/O on the backing file instead
of hacks like this.