Date: Wed, 29 Mar 2017 11:11:14 +0200
From: Peter Zijlstra <peterz@infradead.org>
To: Davidlohr Bueso <dave@stgolabs.net>
Cc: mingo@kernel.org, akpm@linux-foundation.org, jack@suse.cz,
        kirill.shutemov@linux.intel.com, mhocko@suse.com,
        mgorman@techsingularity.net, linux-kernel@vger.kernel.org,
        Davidlohr Bueso <dbueso@suse.de>
Subject: Re: [PATCH 1/5] locking: Introduce range reader/writer lock
Message-ID: <20170329091114.4fgotmjhh7u2v7ga@hirez.programming.kicks-ass.net>
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On Mon, Mar 06, 2017 at 09:03:26PM -0800, Davidlohr Bueso wrote:
> +/*
> + * Implementation of read/write range locks.
> + *
> + * We keep interval tree of locked and to-be-locked ranges. When new range lock
> + * is requested, we add its interval to the tree and store number of intervals
> + * intersecting it to 'blocking_ranges'.
> + *
> + * When a range is unlocked, we again walk intervals that intersect with the
> + * unlocked one and decrement their 'blocking_ranges'. We wake up owner of any
> + * range lock whose 'blocking_ranges' drops to 0. For the shared case, the
> + * 'blocking_ranges' is only incremented if the intersecting range is not marked
> + * as a reader. 

Not a word about fairness and starvation... Such important topics for
lock primitives.

                   In order to mitigate some of the tree walk overhead for
> + * non-intersecting ranges, the tree's min/max values are maintained and consulted
> + * in O(1) in the fastpath.
> + */

Maybe that ought not be here, doesn't seem like a fundamental design
point and would thus be better suited for a comment near where this
implementation detail is located ?