linux-ext4 - Re: ftruncate-mmap: pages are lost after writing to mmaped file.

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Message-Id: <1237906563.24918.184.camel@twins>
Date:	Tue, 24 Mar 2009 15:56:03 +0100
From:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
To:	Jan Kara <jack@...e.cz>
Cc:	Nick Piggin <nickpiggin@...oo.com.au>,
	"Martin J. Bligh" <mbligh@...igh.org>, linux-ext4@...r.kernel.org,
	Ying Han <yinghan@...gle.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	linux-mm <linux-mm@...ck.org>, guichaz@...il.com,
	Alex Khesin <alexk@...gle.com>,
	Mike Waychison <mikew@...gle.com>,
	Rohit Seth <rohitseth@...gle.com>
Subject: Re: ftruncate-mmap: pages are lost after writing to mmaped file.

On Tue, 2009-03-24 at 15:47 +0100, Jan Kara wrote:
> 
> Or we could implement ext3_mkwrite() to allocate buffers already when we
> make page writeable. But it costs some performace (we have to write page
> full of zeros when allocating those buffers, where previously we didn't
> have to do anything) and it's not trivial to make it work if pagesize >
> blocksize (we should not allocate buffers outside of i_size so if i_size
> = 1024, we create just one block in ext3_mkwrite() but then we need to
> allocate more when we extend the file).

I think this is the best option, failing with SIGBUS when we fail to
allocate blocks seems consistent with other filesystems as well.

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