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

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Message-ID: <20200504201641.GV2869@paulmck-ThinkPad-P72>
Date:   Mon, 4 May 2020 13:16:41 -0700
From:   "Paul E. McKenney" <paulmck@...nel.org>
To:     Uladzislau Rezki <urezki@...il.com>
Cc:     Joel Fernandes <joel@...lfernandes.org>,
        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 Mon, May 04, 2020 at 09:51:28PM +0200, Uladzislau Rezki 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.

But adding such a comment would be fine as well.

							Thanx, Paul