linux-kernel - COW page cache for file hole?

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Message-ID: <BANLkTiko7N=1w+Z56vuDcAUw5cHwgPi=1g@mail.gmail.com>
Date:	Wed, 4 May 2011 10:45:42 +0800
From:	Dave Young <hidave.darkstar@...il.com>
To:	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	linux-mm <linux-mm@...ck.org>, linux-fsdevel@...r.kernel.org,
	Wu Fengguang <fengguang.wu@...el.com>
Subject: COW page cache for file hole?

Hi,

During test fengguang's readahead alloc-noretry patch, I have some thoughts

In the 1000 dd case, page cache of sparse file hole are all zero indeed.
So what about make a global zero page for that purpose, fs level know
it is a hole,
when write occurs on that page we can alloc a new page for that.

I have no enough knowledge to implement it so just give out the
question without patch, sorry.
BTW, was there any attempt for this before?

-- 
Regards
dave
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