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[209.132.183.28]) by mx.google.com with ESMTPS id u35si2107134qtk.325.2019.04.18.14.47.29 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Thu, 18 Apr 2019 14:47:29 -0700 (PDT) Received-SPF: pass (google.com: domain of jglisse@redhat.com designates 209.132.183.28 as permitted sender) client-ip=209.132.183.28; Authentication-Results: mx.google.com; spf=pass (google.com: domain of jglisse@redhat.com designates 209.132.183.28 as permitted sender) smtp.mailfrom=jglisse@redhat.com; dmarc=pass (p=NONE sp=NONE dis=NONE) header.from=redhat.com Received: from smtp.corp.redhat.com (int-mx05.intmail.prod.int.phx2.redhat.com [10.5.11.15]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 051B03082B44; Thu, 18 Apr 2019 21:47:28 +0000 (UTC) Received: from redhat.com (unknown [10.20.6.236]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 20A455D70A; Thu, 18 Apr 2019 21:47:23 +0000 (UTC) Date: Thu, 18 Apr 2019 17:47:21 -0400 From: Jerome Glisse To: Laurent Dufour Cc: akpm@linux-foundation.org, mhocko@kernel.org, peterz@infradead.org, kirill@shutemov.name, ak@linux.intel.com, dave@stgolabs.net, jack@suse.cz, Matthew Wilcox , aneesh.kumar@linux.ibm.com, benh@kernel.crashing.org, mpe@ellerman.id.au, paulus@samba.org, Thomas Gleixner , Ingo Molnar , hpa@zytor.com, Will Deacon , Sergey Senozhatsky , sergey.senozhatsky.work@gmail.com, Andrea Arcangeli , Alexei Starovoitov , kemi.wang@intel.com, Daniel Jordan , David Rientjes , Ganesh Mahendran , Minchan Kim , Punit Agrawal , vinayak menon , Yang Shi , zhong jiang , Haiyan Song , Balbir Singh , sj38.park@gmail.com, Michel Lespinasse , Mike Rapoport , linux-kernel@vger.kernel.org, linux-mm@kvack.org, haren@linux.vnet.ibm.com, npiggin@gmail.com, paulmck@linux.vnet.ibm.com, Tim Chen , linuxppc-dev@lists.ozlabs.org, x86@kernel.org Subject: Re: [PATCH v12 01/31] mm: introduce CONFIG_SPECULATIVE_PAGE_FAULT Message-ID: <20190418214721.GA11645@redhat.com> References: <20190416134522.17540-1-ldufour@linux.ibm.com> <20190416134522.17540-2-ldufour@linux.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20190416134522.17540-2-ldufour@linux.ibm.com> User-Agent: Mutt/1.11.3 (2019-02-01) X-Scanned-By: MIMEDefang 2.79 on 10.5.11.15 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.45]); Thu, 18 Apr 2019 21:47:29 +0000 (UTC) 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 Tue, Apr 16, 2019 at 03:44:52PM +0200, Laurent Dufour wrote: > This configuration variable will be used to build the code needed to > handle speculative page fault. > > By default it is turned off, and activated depending on architecture > support, ARCH_HAS_PTE_SPECIAL, SMP and MMU. > > The architecture support is needed since the speculative page fault handler > is called from the architecture's page faulting code, and some code has to > be added there to handle the speculative handler. > > The dependency on ARCH_HAS_PTE_SPECIAL is required because vm_normal_page() > does processing that is not compatible with the speculative handling in the > case ARCH_HAS_PTE_SPECIAL is not set. > > Suggested-by: Thomas Gleixner > Suggested-by: David Rientjes > Signed-off-by: Laurent Dufour Reviewed-by: Jérôme Glisse Small question below > --- > mm/Kconfig | 22 ++++++++++++++++++++++ > 1 file changed, 22 insertions(+) > > diff --git a/mm/Kconfig b/mm/Kconfig > index 0eada3f818fa..ff278ac9978a 100644 > --- a/mm/Kconfig > +++ b/mm/Kconfig > @@ -761,4 +761,26 @@ config GUP_BENCHMARK > config ARCH_HAS_PTE_SPECIAL > bool > > +config ARCH_SUPPORTS_SPECULATIVE_PAGE_FAULT > + def_bool n > + > +config SPECULATIVE_PAGE_FAULT > + bool "Speculative page faults" > + default y > + depends on ARCH_SUPPORTS_SPECULATIVE_PAGE_FAULT > + depends on ARCH_HAS_PTE_SPECIAL && MMU && SMP > + help > + Try to handle user space page faults without holding the mmap_sem. > + > + This should allow better concurrency for massively threaded processes Is there any case where it does not provide better concurrency ? The should make me wonder :) > + since the page fault handler will not wait for other thread's memory > + layout change to be done, assuming that this change is done in > + another part of the process's memory space. This type of page fault > + is named speculative page fault. > + > + If the speculative page fault fails because a concurrent modification > + is detected or because underlying PMD or PTE tables are not yet > + allocated, the speculative page fault fails and a classic page fault > + is then tried. > + > endmenu > -- > 2.21.0 >