linux-ext4 - Re: Enabling h-trees too early?

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Message-ID: <p738x709yrh.fsf@bingen.suse.de>
Date:	21 Sep 2007 11:02:58 +0200
From:	Andi Kleen <andi@...stfloor.org>
To:	Theodore Tso <tytso@....edu>
Cc:	Jan Kara <jack@...e.cz>, linux-ext4@...r.kernel.org
Subject: Re: Enabling h-trees too early?

Theodore Tso <tytso@....edu> writes:
> 
> Certainly one of the things that we could consider is for small
> directories to do an in-memory sort of all of the directory entries at
> opendir() time, and keeping that list until it is closed.  We can't do
> this for really big directories, but we could easily do it for
> directories under 32k or 64k.

I assume you mean sort by inode, because sort by htree key would
be as bad as htrees.

But wouldn't that break parallel readdir for a directory that just grows
from <32/64K to over it?  e.g. if the sort moves already read 
entries to after the  cursor readdir would return some entries twice.

I suspect you would need to keep it always sorted after that no matter
how big it gets. So the 32/64k boundary seems useless and you would
need a sorted potentially partial in memory rbtree anyways.

-Andi
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