linux-kernel - Re: [PATCH v6 4/6] lib/dlock-list: Make sibling CPUs share the same linked list

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Date:   Mon, 9 Oct 2017 09:26:13 +0200
From:   Jan Kara <jack@...e.cz>
To:     Waiman Long <longman@...hat.com>
Cc:     Jan Kara <jack@...e.cz>, Alexander Viro <viro@...iv.linux.org.uk>,
        Jan Kara <jack@...e.com>,
        Jeff Layton <jlayton@...chiereds.net>,
        "J. Bruce Fields" <bfields@...ldses.org>,
        Tejun Heo <tj@...nel.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>,
        Davidlohr Bueso <dave@...olabs.net>,
        Waiman Long <Waiman.Long@....com>
Subject: Re: [PATCH v6 4/6] lib/dlock-list: Make sibling CPUs share the same
 linked list

On Thu 05-10-17 10:57:07, Waiman Long wrote:
> On 10/05/2017 04:59 AM, Jan Kara wrote:
> > On Wed 04-10-17 17:20:05, Waiman Long wrote:
> >>  int alloc_dlock_list_heads(struct dlock_list_heads *dlist)
> >>  {
> >> -	int idx;
> >> +	int idx, cnt = nr_dlock_lists ? nr_dlock_lists : nr_cpu_ids;
> > Hum, is this there for the case where alloc_dlock_list_heads() is called
> > before nr_dlock_lists is initialized? But how can the dlist be used later
> > when it has larger number of lists and you don't know how many?
> 
> The point is nr_dlock_lists <= nr_cpu_ids. Before nr_dlock_lists is
> initialized, the mapping table will map all cpus to the first entry. So
> the extra entries will just stay unused. At free time, they will all get
> de-allocated. I will clarify that with a comment.

OK, nice trick.

								Honza
-- 
Jan Kara <jack@...e.com>
SUSE Labs, CR