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[136.24.99.118]) by smtp.gmail.com with ESMTPSA id r20-20020a634414000000b00421841943dfsm12633501pga.12.2022.09.08.09.15.39 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 08 Sep 2022 09:15:41 -0700 (PDT) Date: Thu, 8 Sep 2022 09:15:37 -0700 From: Dennis Zhou To: Andrew Morton Cc: "Sun, Jiebin" , Tim Chen , vasily.averin@linux.dev, shakeelb@google.com, tj@kernel.org, cl@linux.com, ebiederm@xmission.com, legion@kernel.org, manfred@colorfullife.com, alexander.mikhalitsyn@virtuozzo.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org, tim.c.chen@intel.com, feng.tang@intel.com, ying.huang@intel.com, tianyou.li@intel.com, wangyang.guo@intel.com Subject: Re: [PATCH v4] ipc/msg: mitigate the lock contention with percpu counter Message-ID: References: <20220907172516.1210842-1-jiebin.sun@intel.com> <20220907143427.0ce54bbf096943ffca197fee@linux-foundation.org> <20220908083859.24c989f08d62ddbd031005de@linux-foundation.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20220908083859.24c989f08d62ddbd031005de@linux-foundation.org> ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1662653742; a=rsa-sha256; cv=none; b=qeUnBw9dtPJ2Z2on8L8ZziyT3tP/PxlqU+Zfksnt9bLdVtdlQwPcQLmbjKi2sIPk+tK/fX MzREDZz7ylF33ExvYvEOEyt1RmKreIcjnonKlVE9QZxp9htSMBIBvN9Ns8PixkK09L5WG9 5KG5+ycnJgikYjB2Q+JDw1fADZVJRLI= ARC-Authentication-Results: i=1; imf15.hostedemail.com; dkim=none; dmarc=fail reason="SPF not aligned (relaxed), No valid DKIM" header.from=kernel.org (policy=none); spf=pass (imf15.hostedemail.com: domain of dennisszhou@gmail.com designates 209.85.214.169 as permitted sender) smtp.mailfrom=dennisszhou@gmail.com ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1662653742; h=from:from:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=WRizZ/elGsKzYrgR6wHhu5mQCbmwoq7lJMsQ4A5WuXk=; b=EhQkuJVcYfAE2O1bOjlWgpfcDPDkCOaXFuVoh+2lNvi1fvo9jHHjCsJNiwJ7T6jtf7KyLW o2CM4dNifbn+KR7ggAo5TbH047vmMBy8QALzn9FZ8jAT2Q651s0WU4MNsYldjmxQmQxfmx WzRIA7+DBHez53UcKnGspIItcqjmGk0= X-Rspam-User: X-Stat-Signature: az8unpgjxf8w578uwxqydy3acoyegrrb X-Rspamd-Queue-Id: DD472A007B Authentication-Results: imf15.hostedemail.com; dkim=none; dmarc=fail reason="SPF not aligned (relaxed), No valid DKIM" header.from=kernel.org (policy=none); spf=pass (imf15.hostedemail.com: domain of dennisszhou@gmail.com designates 209.85.214.169 as permitted sender) smtp.mailfrom=dennisszhou@gmail.com X-Rspamd-Server: rspam05 X-HE-Tag: 1662653742-52207 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: Hello, On Thu, Sep 08, 2022 at 08:38:59AM -0700, Andrew Morton wrote: > On Thu, 8 Sep 2022 16:25:47 +0800 "Sun, Jiebin" wrote: > > > In our case, if the local > > percpu counter is near to INT_MAX and there comes a big msgsz, the > > overflow issue could happen. > > percpu_counter_add_batch() handles this - your big message > won't overflow an s64. > > > Lookng at percpu_counter_add_batch(), is this tweak right? > > - don't need to update *fbc->counters inside the lock > - that __this_cpu_sub() is an obscure way of zeroing the thing > > --- a/lib/percpu_counter.c~a > +++ a/lib/percpu_counter.c > @@ -89,8 +89,8 @@ void percpu_counter_add_batch(struct per > unsigned long flags; > raw_spin_lock_irqsave(&fbc->lock, flags); > fbc->count += count; > - __this_cpu_sub(*fbc->counters, count - amount); > raw_spin_unlock_irqrestore(&fbc->lock, flags); > + __this_cpu_write(*fbc->counters, 0); I don't think this is irq safe. It'd be best to leave it inside the spinlock as then we can use __this_cpu_write() to 0 in there. > } else { > this_cpu_add(*fbc->counters, amount); > } > _ > Thanks, Dennis