linux-ext4 - Re: [RFC][PATCH 3/8 v2] ext4: initialize extent status tree

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Message-ID: <20120925205921.GA8625@thunk.org>
Date:	Tue, 25 Sep 2012 16:59:21 -0400
From:	Theodore Ts'o <tytso@....edu>
To:	linux-ext4@...r.kernel.org, linux-fsdevel@...r.kernel.org,
	Yongqiang Yang <xiaoqiangnk@...il.com>,
	Allison Henderson <achender@...ux.vnet.ibm.com>,
	Zheng Liu <wenqing.lz@...bao.com>
Subject: Re: [RFC][PATCH 3/8 v2] ext4: initialize extent status tree

On Tue, Sep 25, 2012 at 08:42:52PM +0800, Zheng Liu wrote:
> > If so, we might want to think about adding a sanity check to make sure
> > that by the time we are done with the inode in ext4_evict_inode()
> > (after we have forced writeback), the ext4_es_tree is empty.  Agreed?
> 
> Today I revise this patch again, and I find extent_status_tree is freed
> in ext4_clear_inode().  So maybe I don't think that we need to check
> this tree to be freed in ext4_evict_inode().  This change is in this
> patch '[RFC][PATCH 4/8 v2] ext4: let ext4 maintain extent status tree'.
> What's your opinion?

When you say "revise this patch again", does that mean that you would
like to submit a new set of patch series with changes?  Or just that
you are looking at this patch set again?

It's certainly true that ext4_evict_inode() will call
ext4_clear_inode(), so it's not a question of worrying about a memory
leak.  I was thinking more about doing this as a cheap sanity check
for the data structure.  By the time we call ext4_evict_inode(), the
mm layer all writeback should be complete.  Hence, all of the entries
to the tree _should_ have been removed by the time we call
ext4_evict_inode().

I don't know if this is going to change as you start using this data
structure for other purposes (such as locking a range of pages), but
if I understand how things are currently working, it _should_ be the
case that when ext4_evict_inode() calls ext4_clear_inode(), the call
to ext4_es_remove_extent() should be a no-op, since all of the nodes
in the extent status tree should have been released by then.  If it
isn't, then either I'm not understanding the code, or there's a bug in
the code.

						- Ted
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