linux-kernel - Re: [RFC PATCH v2 6/7] lib/persubnode: Introducing a simple per-subnode APIs

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Message-ID: <20160712185718.GH3190@htj.duckdns.org>
Date:	Tue, 12 Jul 2016 14:57:18 -0400
From:	Tejun Heo <tj@...nel.org>
To:	Waiman Long <waiman.long@....com>
Cc:	Alexander Viro <viro@...iv.linux.org.uk>, Jan Kara <jack@...e.com>,
	Jeff Layton <jlayton@...chiereds.net>,
	"J. Bruce Fields" <bfields@...ldses.org>,
	Christoph Lameter <cl@...ux-foundation.org>,
	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
	Ingo Molnar <mingo@...hat.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Andi Kleen <andi@...stfloor.org>,
	Dave Chinner <dchinner@...hat.com>,
	Boqun Feng <boqun.feng@...il.com>,
	Scott J Norton <scott.norton@....com>,
	Douglas Hatch <doug.hatch@....com>
Subject: Re: [RFC PATCH v2 6/7] lib/persubnode: Introducing a simple
 per-subnode APIs

Hello,

On Tue, Jul 12, 2016 at 02:51:31PM -0400, Waiman Long wrote:
> The last 2 RFC patches were created in response to Andi's comment to have
> coarser granularity than per-cpu. In this particular use case, I don't think
> global list traversals are frequent enough to really have any noticeable
> performance impact. So I don't have any benchmark number to support this
> change. However, it may not be true for other future use cases.
> 
> These 2 patches were created to gauge if using a per-subnode API for this
> use case is a good idea or not. I am perfectly happy to keep it as per-cpu
> and scrap the last 2 RFC patches. My main goal is to make this patchset more
> acceptable to be moved forward instead of staying in limbo.

I see.  I don't think it makes sense to add a whole new API for a use
case which doesn't really need it without any backing data.  It
probably would be best to revisit this when we're dealing with an
actually problematic case.

Thanks.

-- 
tejun