From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <linux-fsdevel-owner@vger.kernel.org>
Received: from mx1.redhat.com ([209.132.183.28]:57318 "EHLO mx1.redhat.com"
        rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP
        id S1751324AbdKANQw (ORCPT <rfc822;linux-fsdevel@vger.kernel.org>);
        Wed, 1 Nov 2017 09:16:52 -0400
Subject: Re: [PATCH v8 5/6] lib/dlock-list: Enable faster lookup with hashing
To: Jan Kara <jack@suse.cz>
Cc: Alexander Viro <viro@zeniv.linux.org.uk>, Jan Kara <jack@suse.com>,
        Jeff Layton <jlayton@poochiereds.net>,
        "J. Bruce Fields" <bfields@fieldses.org>,
        Tejun Heo <tj@kernel.org>,
        Christoph Lameter <cl@linux-foundation.org>,
        linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org,
        Ingo Molnar <mingo@redhat.com>,
        Peter Zijlstra <peterz@infradead.org>,
        Andi Kleen <andi@firstfloor.org>,
        Dave Chinner <dchinner@redhat.com>,
        Boqun Feng <boqun.feng@gmail.com>,
        Davidlohr Bueso <dave@stgolabs.net>
References: <1509475860-16139-1-git-send-email-longman@redhat.com>
 <1509475860-16139-6-git-send-email-longman@redhat.com>
 <20171101084021.GL26128@quack2.suse.cz>
From: Waiman Long <longman@redhat.com>
Message-ID: <61a2ff76-8f5c-30e5-5645-76ca07ba77f0@redhat.com>
Date: Wed, 1 Nov 2017 09:16:49 -0400
MIME-Version: 1.0
In-Reply-To: <20171101084021.GL26128@quack2.suse.cz>
Content-Type: text/plain; charset=utf-8
Content-Transfer-Encoding: 7bit
Content-Language: en-US
Sender: linux-fsdevel-owner@vger.kernel.org
List-ID: <linux-fsdevel.vger.kernel.org>

On 11/01/2017 04:40 AM, Jan Kara wrote:
> On Tue 31-10-17 14:50:59, Waiman Long wrote:
>> Insertion and deletion is relatively cheap and mostly contention
>> free for dlock-list. Lookup, on the other hand, can be rather costly
>> because all the lists in a dlock-list will have to be iterated.
>>
>> Currently dlock-list insertion is based on the cpu that the task is
>> running on. So a given object can be inserted into any one of the
>> lists depending on what the current cpu is.
>>
>> This patch provides an alternative way of list selection. The caller
>> can provide a object context which will be hashed to one of the list
>> in a dlock-list. The object can then be added into that particular
>> list. Lookup can be done by iterating elements in the provided list
>> only instead of all the lists in a dlock-list.
>>
>> The new APIs are:
>>
>> struct dlock_list_head *dlock_list_hash(struct dlock_list_heads *, void *);
>> void dlock_list_add(struct dlock_list_node *, struct dlock_list_head *);
>>
>> Signed-off-by: Waiman Long <longman@redhat.com>
> Hum, do we have any users for this API? And wouldn't they also need to
> control how many lists are allocated then?

This patch is supposed to be used by the epoll patch from Davidlohr. As
he has retracted the patch, I can drop this patch also. The number of
lists scale with the number of CPU cores in the system whether it is
used one way or the others.

Cheers,
Longman