From: "Paul E. McKenney" <paulmck@kernel.org>
To: Michal Hocko <mhocko@suse.com>
Cc: rcu@vger.kernel.org, linux-kernel@vger.kernel.org,
kernel-team@fb.com, mingo@kernel.org, jiangshanlai@gmail.com,
akpm@linux-foundation.org, mathieu.desnoyers@efficios.com,
josh@joshtriplett.org, tglx@linutronix.de, peterz@infradead.org,
rostedt@goodmis.org, dhowells@redhat.com, edumazet@google.com,
fweisbec@gmail.com, oleg@redhat.com, joel@joelfernandes.org,
mgorman@techsingularity.net, torvalds@linux-foundation.org,
"Uladzislau Rezki (Sony)" <urezki@gmail.com>
Subject: Re: [PATCH tip/core/rcu 14/15] rcu/tree: Allocate a page when caller is preemptible
Date: Thu, 1 Oct 2020 09:28:35 -0700 [thread overview]
Message-ID: <20201001162835.GE29330@paulmck-ThinkPad-P72> (raw)
In-Reply-To: <20201001090220.GA22560@dhcp22.suse.cz>
On Thu, Oct 01, 2020 at 11:02:20AM +0200, Michal Hocko wrote:
> On Wed 30-09-20 16:21:54, Paul E. McKenney wrote:
[ . . . ]
Hit "send" too soon, apologies...
> > ------------------------------------------------------------------------
> >
> > commit 490b638d7c241ac06cee168ccf8688bb8b872478
> > Author: Paul E. McKenney <paulmck@kernel.org>
> > Date: Wed Sep 30 16:16:39 2020 -0700
> >
> > kvfree_rcu(): Switch from kmalloc/kfree to __get_free_page/free_page.
> >
> > The advantages of using kmalloc() and kfree() are a possible small speedup
> > on CONFIG_SLAB=y systems, avoiding the allocation-side cast, and use of
> > more-familiar API members. The advantages of using __get_free_page()
> > and free_page() are a possible reduction in fragmentation and direct
> > access to the buddy allocator.
> >
> > To help settle the question as to which to use, this commit switches
> > from kmalloc() and kfree() to __get_free_page() and free_page().
> >
> > Suggested-by: Michal Hocko <mhocko@suse.com>
> > Suggested-by: "Uladzislau Rezki (Sony)" <urezki@gmail.com>
> > Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
>
> Yes, looks good to me. I am not entirely sure about the fragmentation
> argument. It really depends on the SL.B allocator internals. The same
> applies for the potential speed up. I would be even surprised if the
> SLAB was faster in average considering it has to use the page allocator
> as well. So to me the primary motivation would be "use the right tool
> for the purpose".
Very well, I will update the commit message, and thank you!
Thanx, Paul
> > diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
> > index 2886e81..242f0f0 100644
> > --- a/kernel/rcu/tree.c
> > +++ b/kernel/rcu/tree.c
> > @@ -3225,7 +3225,8 @@ static void kfree_rcu_work(struct work_struct *work)
> > bkvhead[i] = NULL;
> > krc_this_cpu_unlock(krcp, flags);
> >
> > - kfree(bkvhead[i]);
> > + if (bkvhead[i])
> > + free_page((unsigned long)bkvhead[i]);
> >
> > cond_resched_tasks_rcu_qs();
> > }
> > @@ -3378,7 +3379,7 @@ add_ptr_to_bulk_krc_lock(struct kfree_rcu_cpu **krcp,
> > bnode = get_cached_bnode(*krcp);
> > if (!bnode && can_alloc_page) {
> > krc_this_cpu_unlock(*krcp, *flags);
> > - bnode = kmalloc(PAGE_SIZE, gfp);
> > + bnode = (struct kvfree_rcu_bulk_data *)__get_free_page(gfp);
> > *krcp = krc_this_cpu_lock(flags);
> > }
> >
>
> --
> Michal Hocko
> SUSE Labs
next prev parent reply other threads:[~2020-10-01 16:28 UTC|newest]
Thread overview: 30+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-09-28 23:30 [PATCH tip/core/rcu 0/15] Paul E. McKenney
2020-09-28 23:30 ` [PATCH tip/core/rcu 01/15] lib/debug: Remove pointless ARCH_NO_PREEMPT dependencies paulmck
2020-09-28 23:30 ` [PATCH tip/core/rcu 02/15] preempt: Make preempt count unconditional paulmck
2020-09-28 23:30 ` [PATCH tip/core/rcu 03/15] preempt: Cleanup PREEMPT_COUNT leftovers paulmck
2020-09-28 23:30 ` [PATCH tip/core/rcu 04/15] lockdep: " paulmck
2020-09-28 23:30 ` [PATCH tip/core/rcu 05/15] mm/pagemap: " paulmck
2020-09-28 23:30 ` [PATCH tip/core/rcu 06/15] locking/bitspinlock: " paulmck
2020-09-28 23:30 ` [PATCH tip/core/rcu 07/15] uaccess: " paulmck
2020-09-28 23:30 ` [PATCH tip/core/rcu 08/15] sched: " paulmck
2020-09-28 23:30 ` [PATCH tip/core/rcu 09/15] ARM: " paulmck
2020-09-28 23:30 ` [PATCH tip/core/rcu 10/15] xtensa: " paulmck
2020-09-28 23:30 ` [PATCH tip/core/rcu 11/15] drm/i915: " paulmck
2020-10-01 7:17 ` Joonas Lahtinen
2020-10-01 8:25 ` Thomas Gleixner
2020-10-01 16:03 ` Paul E. McKenney
2020-09-28 23:30 ` [PATCH tip/core/rcu 12/15] rcutorture: " paulmck
2020-09-28 23:31 ` [PATCH tip/core/rcu 13/15] preempt: Remove PREEMPT_COUNT from Kconfig paulmck
2020-09-28 23:31 ` [PATCH tip/core/rcu 14/15] rcu/tree: Allocate a page when caller is preemptible paulmck
2020-09-29 12:07 ` Michal Hocko
2020-09-30 1:53 ` Paul E. McKenney
2020-09-30 8:41 ` Michal Hocko
2020-09-30 12:31 ` Uladzislau Rezki
2020-09-30 23:21 ` Paul E. McKenney
2020-10-01 9:02 ` Michal Hocko
2020-10-01 16:27 ` Paul E. McKenney
2020-10-02 6:57 ` Michal Hocko
2020-10-02 14:12 ` Paul E. McKenney
2020-10-01 16:28 ` Paul E. McKenney [this message]
2020-10-01 20:03 ` Uladzislau Rezki
2020-09-28 23:31 ` [PATCH tip/core/rcu 15/15] kvfree_rcu(): Fix ifnullfree.cocci warnings paulmck
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