linux-ext4 - Re: [PATCH, RFC] ext4: Remove i_ext_generation from ext4_inode

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Message-id: <491564F0.4030502@sun.com>
Date:	Sat, 08 Nov 2008 13:07:44 +0300
From:	Alex Zhuravlev <Alex.Zhuravlev@....COM>
To:	Andreas Dilger <adilger@....COM>
Cc:	"Theodore Ts'o" <tytso@....edu>, linux-ext4@...r.kernel.org
Subject: Re: [PATCH, RFC] ext4: Remove i_ext_generation from	ext4_inode_info
 structure

Andreas Dilger wrote:
> On Nov 04, 2008  18:47 -0500, Theodore Ts'o wrote:
>> ext4_inode_info.i_ext_generation isn't used by anything.  Was there an
>> intent to use it for something in the future?
> 
> Alex was going to use this at one point in the future, but it never
> happened.

actually it was used by delayed allocation patch as walk_space() takes
truncate_sem, then, if block isn't allocated yet, start transaction which
we can't do holding truncate_sem. so the idea is to release truncate_sem,
start transaction, then acquire truncate_sem. but in this window the tree
can change making path structure obsolete. either we check tree hasn't
changed or use generation to avoid unneeded path revalidation?

thanks, Alex

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