linux-kernel - Re: [PATCH 09/24] rcu/tree: cache specified number of objects

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Message-ID: <2A623E6F-878C-4C1F-9045-56710DE7851B@joelfernandes.org>
Date:   Mon, 04 May 2020 16:15:55 -0400
From:   joel@...lfernandes.org
To:     Uladzislau Rezki <urezki@...il.com>,
        "Paul E. McKenney" <paulmck@...nel.org>
CC:     LKML <linux-kernel@...r.kernel.org>, linux-mm <linux-mm@...ck.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        "Theodore Y . Ts'o" <tytso@....edu>,
        Matthew Wilcox <willy@...radead.org>,
        RCU <rcu@...r.kernel.org>,
        Oleksiy Avramchenko <oleksiy.avramchenko@...ymobile.com>
Subject: Re: [PATCH 09/24] rcu/tree: cache specified number of objects



On May 4, 2020 3:51:28 PM EDT, Uladzislau Rezki <urezki@...il.com> wrote:
>> > > Since we don't care about traversing backwards, isn't it better
>to use llist
>> > > for this usecase?
>> > >
>> > > I think Vlad is using locking as we're also tracking the size of
>the llist to
>> > > know when to free pages. This tracking could suffer from the
>lost-update
>> > > problem without any locking, 2 lockless llist_add happened
>simulatenously.
>> > >
>> > > Also if list_head is used, it will take more space and still use
>locking.
>> >
>> > Indeed, it would be best to use a non-concurrent singly linked
>list.
>> 
>> Ok cool :-)
>> 
>> Is it safe to say something like the following is ruled out? ;-) :-D
>> #define kfree_rcu_list_add llist_add
>> 
>In that case i think it is better just to add a comment about using
>llist_head. To state that it used as a singular list to save space
>and the access is synchronized by the lock :)
>
>IMHO.

Sounds good to me. thanks,

 - Joel

>
>--
>Vlad Rezki

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