linux-ext4 - Re: Checks in ext4_ext_fiemap

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Date:	Tue, 26 Jul 2011 10:44:28 -0600
From:	Andreas Dilger <adilger@...ger.ca>
To:	Yongqiang Yang <xiaoqiangnk@...il.com>
Cc:	Ted Ts'o <tytso@....edu>,
	Ext4 Developers List <linux-ext4@...r.kernel.org>
Subject: Re: Checks in ext4_ext_fiemap_cb() broken

On Tue 26-07-11 09:20:28, Yongqiang Yang wrote:
> I have been thinking if we can handle fiemap much simpler for a while.
> Current code is very ugly due to page cache look up.  I have a
> thought on simplifying these code.  The reason leading us to looking
> up page cache is that delayed extents are not in extents tree.  I
> think we can add an in-memory delayed extents list in inode, and we
> can delete entries in the list after we allocate blocks for them.
> There is no limit on length of extents in the list, this way can an
> entry contain as many blocks as they are contiguous logically.
> 
> What's your opinion?

It may also be useful to have an extent list for submitting large contiguous writeouts to disk, instead of having to look them up.

The main question is whether the added overhead of maintaining the list is worthwhile if we can get an equivalent functionality using a tag lookup in the page cache.

Cheers, Andreas





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