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[94.245.46.61]) by smtp.gmail.com with ESMTPSA id 13sm2327929lft.5.2021.01.30.03.21.54 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sat, 30 Jan 2021 03:21:54 -0800 (PST) From: Uladzislau Rezki X-Google-Original-From: Uladzislau Rezki Date: Sat, 30 Jan 2021 12:21:52 +0100 To: "Zhang, Qiang" Cc: Uladzislau Rezki , "paulmck@kernel.org" , "joel@joelfernandes.org" , "rcu@vger.kernel.org" , "linux-kernel@vger.kernel.org" Subject: Re: =?utf-8?B?5Zue5aSNOiBbUEFUQw==?= =?utf-8?Q?H?= v2] kvfree_rcu: Release page cache under memory pressure Message-ID: <20210130112152.GA1977@pc636> References: <20210129080442.16055-1-qiang.zhang@windriver.com> <20210129141953.GA29827@pc638.lan> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: User-Agent: Mutt/1.10.1 (2018-07-13) Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sat, Jan 30, 2021 at 06:47:31AM +0000, Zhang, Qiang wrote: > > > ________________________________________ > 发件人: Uladzislau Rezki > 发送时间: 2021年1月29日 22:19 > 收件人: Zhang, Qiang > 抄送: urezki@gmail.com; paulmck@kernel.org; joel@joelfernandes.org; rcu@vger.kernel.org; linux-kernel@vger.kernel.org > 主题: Re: [PATCH v2] kvfree_rcu: Release page cache under memory pressure > > [Please note: This e-mail is from an EXTERNAL e-mail address] > > On Fri, Jan 29, 2021 at 04:04:42PM +0800, qiang.zhang@windriver.com wrote: > > From: Zqiang > > > > Add free per-cpu existing krcp's page cache operation, when > > the system is under memory pressure. > > > > Signed-off-by: Zqiang > > --- > > kernel/rcu/tree.c | 25 +++++++++++++++++++++++++ > > 1 file changed, 25 insertions(+) > > > > diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c > > index c1ae1e52f638..ec098910d80b 100644 > > --- a/kernel/rcu/tree.c > > +++ b/kernel/rcu/tree.c > > @@ -3571,17 +3571,40 @@ void kvfree_call_rcu(struct rcu_head *head, rcu_callback_t func) > > } > > EXPORT_SYMBOL_GPL(kvfree_call_rcu); > > > > +static int free_krc_page_cache(struct kfree_rcu_cpu *krcp) > > +{ > > + unsigned long flags; > > + struct kvfree_rcu_bulk_data *bnode; > > + int i; > > + > > + for (i = 0; i < rcu_min_cached_objs; i++) { > > + raw_spin_lock_irqsave(&krcp->lock, flags); > >I am not sure why we should disable IRQs. I think it can be >avoided. > > Suppose in multi CPU system, the kfree_rcu_shrink_scan function is runing on CPU2, > and we just traverse to CPU2, and then call free_krc_page_cache function, > if not disable irq, a interrupt may be occurs on CPU2 after the CPU2 corresponds to krcp variable 's lock be acquired, if the interrupt or softirq handler function to call kvfree_rcu function, in this function , acquire CPU2 corresponds to krcp variable 's lock , will happen deadlock. > Or in single CPU scenario. > Right. Deadlock scenario. It went away from my head during writing that :) Thanks! -- Vlad Rezki