From: Uladzislau Rezki <urezki@gmail.com>
To: Peter Zijlstra <peterz@infradead.org>
Cc: Uladzislau Rezki <urezki@gmail.com>,
Mel Gorman <mgorman@techsingularity.net>,
"Paul E. McKenney" <paulmck@kernel.org>,
Michal Hocko <mhocko@suse.com>,
LKML <linux-kernel@vger.kernel.org>, RCU <rcu@vger.kernel.org>,
linux-mm@kvack.org, Andrew Morton <akpm@linux-foundation.org>,
Vlastimil Babka <vbabka@suse.cz>,
Thomas Gleixner <tglx@linutronix.de>,
"Theodore Y . Ts'o" <tytso@mit.edu>,
Joel Fernandes <joel@joelfernandes.org>,
Sebastian Andrzej Siewior <bigeasy@linutronix.de>,
Oleksiy Avramchenko <oleksiy.avramchenko@sonymobile.com>,
Mel Gorman <mgorman@suse.de>
Subject: Re: [RFC-PATCH 2/4] mm: Add __rcu_alloc_page_lockless() func.
Date: Thu, 24 Sep 2020 17:21:12 +0200 [thread overview]
Message-ID: <20200924152112.GB19013@pc636> (raw)
In-Reply-To: <20200924111907.GE2628@hirez.programming.kicks-ass.net>
On Thu, Sep 24, 2020 at 01:19:07PM +0200, Peter Zijlstra wrote:
> On Thu, Sep 24, 2020 at 10:16:14AM +0200, Uladzislau Rezki wrote:
> > The key point is "enough". We need pages to make a) fast progress b) support
> > single argument of kvfree_rcu(one_arg). Not vice versa. That "enough" depends
> > on scheduler latency and vague pre-allocated number of pages, it might
> > be not enough what would require to refill it more and more or we can overshoot
> > that would lead to memory overhead. So we have here timing issues and
> > not accurate model. IMHO.
>
> I'm firmly opposed to the single argument kvfree_rcu() idea, that's
> requiring memory to free memory.
>
Hmm.. The problem is there is a demand in it:
Please have a look at places in the kernel where people do not
embed the rcu_head into their stuctures and do like:
<snip>
synchronize_rcu();
kfree(p);
<snip>
<snip>
urezki@pc638:~/data/coding/linux-rcu.git$ find ./ -name "*.c" | xargs grep -C 1 -rn "synchronize_rcu" | grep kfree
./fs/nfs/sysfs.c-113- kfree(old);
./fs/ext4/super.c-1708- kfree(old_qname);
./kernel/trace/ftrace.c-5079- kfree(direct);
./kernel/trace/ftrace.c-5156- kfree(direct);
./kernel/trace/trace_probe.c-1087- kfree(link);
./kernel/module.c-3910- kfree(mod->args);
./net/core/sysctl_net_core.c-143- kfree(cur);
./arch/x86/mm/mmio-mod.c-314- kfree(found_trace);
./drivers/mfd/dln2.c-183- kfree(i);
./drivers/block/drbd/drbd_state.c-2074- kfree(old_conf);
./drivers/block/drbd/drbd_nl.c-1689- kfree(old_disk_conf);
./drivers/block/drbd/drbd_nl.c-2522- kfree(old_net_conf);
./drivers/block/drbd/drbd_nl.c-2935- kfree(old_disk_conf);
./drivers/block/drbd/drbd_receiver.c-3805- kfree(old_net_conf);
./drivers/block/drbd/drbd_receiver.c-4177- kfree(old_disk_conf);
./drivers/ipack/carriers/tpci200.c-189- kfree(slot_irq);
./drivers/crypto/nx/nx-842-pseries.c-1010- kfree(old_devdata);
./drivers/net/ethernet/myricom/myri10ge/myri10ge.c-3583- kfree(mgp->ss);
./drivers/net/ethernet/mellanox/mlx5/core/fpga/tls.c:286: synchronize_rcu(); /* before kfree(flow) */
./drivers/net/ethernet/mellanox/mlxsw/core.c-1574- kfree(rxl_item);
./drivers/net/ethernet/chelsio/cxgb4/cxgb4_main.c-6642- kfree(adapter->mbox_log);
./drivers/net/ethernet/chelsio/cxgb4/cxgb4_main.c-6644- kfree(adapter);
./drivers/infiniband/hw/hfi1/sdma.c-1337- kfree(dd->per_sdma);
./drivers/infiniband/core/device.c:2164: * synchronize_rcu before the netdev is kfreed, so we
./drivers/misc/vmw_vmci/vmci_context.c-692- kfree(notifier);
./drivers/misc/vmw_vmci/vmci_event.c-213- kfree(s);
./drivers/staging/fwserial/fwserial.c-2122- kfree(peer);
urezki@pc638:~/data/coding/linux-rcu.git$
<snip>
--
Vlad Rezki
next prev parent reply other threads:[~2020-09-24 15:21 UTC|newest]
Thread overview: 76+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-09-18 19:48 [PATCH 0/4] kvfree_rcu() and _LOCK_NESTING/_PREEMPT_RT Uladzislau Rezki (Sony)
2020-09-18 19:48 ` [PATCH 1/4] rcu/tree: Add a work to allocate pages from regular context Uladzislau Rezki (Sony)
2020-09-18 19:48 ` [RFC-PATCH 2/4] mm: Add __rcu_alloc_page_lockless() func Uladzislau Rezki (Sony)
2020-09-21 7:47 ` Michal Hocko
2020-09-21 15:45 ` Paul E. McKenney
2020-09-21 16:03 ` Michal Hocko
2020-09-21 19:48 ` Uladzislau Rezki
2020-09-22 7:50 ` Michal Hocko
2020-09-22 13:12 ` Uladzislau Rezki
2020-09-22 15:35 ` Michal Hocko
2020-09-23 10:37 ` Mel Gorman
2020-09-23 15:41 ` Paul E. McKenney
2020-09-23 23:22 ` Mel Gorman
2020-09-24 8:16 ` Uladzislau Rezki
2020-09-24 11:16 ` Peter Zijlstra
2020-09-24 15:16 ` Uladzislau Rezki
2020-09-24 11:19 ` Peter Zijlstra
2020-09-24 15:21 ` Uladzislau Rezki [this message]
2020-09-25 8:15 ` Peter Zijlstra
2020-09-25 10:25 ` Uladzislau Rezki
2020-09-24 15:38 ` Paul E. McKenney
2020-09-25 8:26 ` Peter Zijlstra
2020-09-26 14:37 ` Paul E. McKenney
2020-09-25 8:05 ` Michal Hocko
2020-09-25 15:31 ` Uladzislau Rezki
2020-09-25 15:47 ` Michal Hocko
2020-09-29 16:25 ` Uladzislau Rezki
2020-09-30 9:27 ` Michal Hocko
2020-09-30 12:35 ` Uladzislau Rezki
2020-09-30 12:44 ` Michal Hocko
2020-09-30 13:39 ` Uladzislau Rezki
2020-09-30 16:46 ` Michal Hocko
2020-09-30 20:36 ` Uladzislau Rezki
2020-09-30 15:25 ` Joel Fernandes
2020-09-30 16:48 ` Michal Hocko
2020-09-30 17:03 ` Joel Fernandes
2020-09-30 17:22 ` Michal Hocko
2020-09-30 17:48 ` Joel Fernandes
2020-09-25 16:17 ` Mel Gorman
2020-09-25 17:57 ` Uladzislau Rezki
2020-09-22 15:49 ` Paul E. McKenney
2020-09-22 3:35 ` Paul E. McKenney
2020-09-22 8:03 ` Michal Hocko
2020-09-22 15:46 ` Paul E. McKenney
2020-09-23 11:27 ` Uladzislau Rezki
2020-09-29 10:15 ` Vlastimil Babka
2020-09-29 22:07 ` Uladzislau Rezki
2020-09-30 10:35 ` Michal Hocko
2020-10-01 19:32 ` Uladzislau Rezki
2020-09-30 14:39 ` Vlastimil Babka
2020-09-30 15:37 ` Joel Fernandes
2020-10-01 19:26 ` Uladzislau Rezki
2020-10-02 7:11 ` Michal Hocko
2020-10-02 8:50 ` Mel Gorman
2020-10-02 9:05 ` Michal Hocko
2020-10-05 15:08 ` Uladzislau Rezki
2020-10-05 15:41 ` Michal Hocko
2020-10-06 22:25 ` Uladzislau Rezki
2020-10-07 10:02 ` Michal Hocko
2020-10-07 11:02 ` Uladzislau Rezki
2020-10-02 9:07 ` Peter Zijlstra
2020-10-02 9:45 ` Mel Gorman
2020-10-02 9:58 ` Peter Zijlstra
2020-10-02 10:19 ` Mel Gorman
2020-10-02 14:41 ` Paul E. McKenney
2020-10-06 10:03 ` Mel Gorman
2020-10-06 15:41 ` Paul E. McKenney
2020-10-05 13:58 ` Uladzislau Rezki
2020-10-02 8:06 ` Mel Gorman
2020-10-05 14:12 ` Uladzislau Rezki
2020-09-18 19:48 ` [PATCH 3/4] rcu/tree: use " Uladzislau Rezki (Sony)
2020-09-18 19:48 ` [PATCH 4/4] rcu/tree: Use schedule_delayed_work() instead of WQ_HIGHPRI queue Uladzislau Rezki (Sony)
2020-09-20 15:06 ` Paul E. McKenney
2020-09-21 13:27 ` Uladzislau Rezki
2020-09-18 22:15 ` [PATCH 0/4] kvfree_rcu() and _LOCK_NESTING/_PREEMPT_RT Paul E. McKenney
2020-09-30 15:52 ` Joel Fernandes
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