Re: dentry bloat.

From: Linus Torvalds
Date: Sat May 08 2004 - 14:16:20 EST

On Sat, 8 May 2004, Andrew Morton wrote:
> I think we can simply take ->d_lock a bit earlier in __d_lookup. That will
> serialise against d_move(), fixing the problem which you mention, and also
> makes d_movecount go away.

If you do that, RCU basically loses most of it's meaning.

You'll be taking a lock for - and dirtying in the cache - every single
dentry on the hash chain, which is pretty much guaranteed to be slower
than just taking the dcache_lock _once_, even if that one jumps across
CPU's a lot.

In other words, no, I don't think that's a good idea. We really want to
take the dentry lock only after we're pretty sure we have the right
dentry. Otherwise the dentry chains will be bouncing from CPU to CPU all
the time.

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