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Date:	Tue, 4 Jun 2013 01:22:03 -0400
From:	Theodore Ts'o <>
To:	宋柏翰 <>
Subject: Re: Question on delalloc

On Tue, Jun 04, 2013 at 03:00:29AM +0800, 宋柏翰 wrote:
> Also after I traced into filemap_write_and_wait_range, I found it
> eventually calls ext4_writepage to do the most part of work, which in
> its comment says "We don't do any block allocation in this function."
> So, can anyone kindly shed any light on my question, or point out my mistakes?

There are three possible address_space_operations structures that can
be used for ext4 files.  They are ext4_aops, ext4_journalled_aops, and
ext4_da_aops.  It is the last one which is used for delayed allocation
files, and in that case filemap_write_and_wait_range will use

These days, if there is an writepages function, the writepage function
is not used at all.  It used to be used for direct reclaim, but that's
been replaced by I/O-less reclaim.

						- Ted
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