From mboxrd@z Thu Jan  1 00:00:00 1970
From: Al Viro <viro@ZenIV.linux.org.uk>
Subject: Re: [PATCH 07/19] quota: make per-sb hash array
Date: Wed, 27 Oct 2010 20:31:09 +0100
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Cc: linux-fsdevel@vger.kernel.org, jack@suse.cz, hch@infradead.org,
	Dmitry Monakhov <dmonakhov@gmail.com>
To: Dmitry Monakhov <dmonakhov@openvz.org>
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On Fri, Oct 22, 2010 at 09:34:52PM +0400, Dmitry Monakhov wrote:
> From: Dmitry Monakhov <dmonakhov@gmail.com>
> 
> Currently quota_hash[] is global, which is bad for scalability.
> Also is is the last user of global dq_list_lock.
> It is reasonable to introduce dedicated hash for each super_block
> which use quota.
> 
> per-sb hash will be allocated only when necessary (on first quota_on())
> Protected by per-sb dq_list_lock.

Ugh...  Why not a common hash with per-chain spinlock?  We'll waste less
memory on those than on hash chain heads even for a couple of superblocks
and unless you've got boxen with more (quota'd) superblocks than hash chains,
you'll get less contention...