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[2607:7c80:54:e::133]) by mx.google.com with ESMTPS id t5si6110323plr.124.2019.07.21.14.09.06 for (version=TLS1_3 cipher=AEAD-AES256-GCM-SHA384 bits=256/256); Sun, 21 Jul 2019 14:09:06 -0700 (PDT) Received-SPF: pass (google.com: best guess record for domain of willy@infradead.org designates 2607:7c80:54:e::133 as permitted sender) client-ip=2607:7c80:54:e::133; Authentication-Results: mx.google.com; dkim=pass header.i=@infradead.org header.s=bombadil.20170209 header.b=hOxpb6w1; spf=pass (google.com: best guess record for domain of willy@infradead.org designates 2607:7c80:54:e::133 as permitted sender) smtp.mailfrom=willy@infradead.org DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=bombadil.20170209; h=In-Reply-To:Content-Type:MIME-Version :References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Id: List-Help:List-Unsubscribe:List-Subscribe:List-Post:List-Owner:List-Archive; bh=m+ymzWwJthSyMsIrAZa5UVM+lb+OeBZIRhgzMglbtss=; b=hOxpb6w1+7znVOU/LYcc4TCsi AU34x9DctQ72CdFA2SbXaxcS1FbGoIVqML8MnXJToxuML6SZi8848XN5DS9AVL0Z9wQgsUK2KRVeI Wz7K+4anU/cZMplgZTFu8tTBeFDdLQlK+4EzYTlmpy18b/zeZMWzGbE65oBnEfAvV8IKyijqNY5Kz B1UEaYbbU2KZci/M3mW5svS0g1vE2DZjApbLyiTi9LrqIkXtIvvBRXC3Hu/WKpOP6J4pBN/jLFKkT nwP8xiN5kn2rcd2USEhk/o97boU6FKRBx8S2WJNurFZKhP65CJgPUJfkVoDYo/kddkcDF3S5fnxNx q3ODFsGGQ==; Received: from willy by bombadil.infradead.org with local (Exim 4.92 #3 (Red Hat Linux)) id 1hpJ4P-00031q-HE; Sun, 21 Jul 2019 21:08:37 +0000 Date: Sun, 21 Jul 2019 14:08:37 -0700 From: Matthew Wilcox To: "Paul E. McKenney" Cc: "Michael S. Tsirkin" , aarcange@redhat.com, akpm@linux-foundation.org, christian@brauner.io, davem@davemloft.net, ebiederm@xmission.com, elena.reshetova@intel.com, guro@fb.com, hch@infradead.org, james.bottomley@hansenpartnership.com, jasowang@redhat.com, jglisse@redhat.com, keescook@chromium.org, ldv@altlinux.org, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, linux-parisc@vger.kernel.org, luto@amacapital.net, mhocko@suse.com, mingo@kernel.org, namit@vmware.com, peterz@infradead.org, syzkaller-bugs@googlegroups.com, viro@zeniv.linux.org.uk, wad@chromium.org Subject: Re: RFC: call_rcu_outstanding (was Re: WARNING in __mmdrop) Message-ID: <20190721210837.GC363@bombadil.infradead.org> References: <0000000000008dd6bb058e006938@google.com> <000000000000964b0d058e1a0483@google.com> <20190721044615-mutt-send-email-mst@kernel.org> <20190721081933-mutt-send-email-mst@kernel.org> <20190721131725.GR14271@linux.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190721131725.GR14271@linux.ibm.com> User-Agent: Mutt/1.11.4 (2019-03-13) 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: On Sun, Jul 21, 2019 at 06:17:25AM -0700, Paul E. McKenney wrote: > Also, the overhead is important. For example, as far as I know, > current RCU gracefully handles close(open(...)) in a tight userspace > loop. But there might be trouble due to tight userspace loops around > lighter-weight operations. I thought you believed that RCU was antifragile, in that it would scale better as it was used more heavily? Would it make sense to have call_rcu() check to see if there are many outstanding requests on this CPU and if so process them before returning? That would ensure that frequent callers usually ended up doing their own processing.