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[2a0a:51c0:0:12e:550::1]) by mx.google.com with ESMTPS id v14si2781866wrw.154.2019.07.10.09.45.23 for (version=TLS1_2 cipher=AES128-SHA bits=128/128); Wed, 10 Jul 2019 09:45:24 -0700 (PDT) Received-SPF: pass (google.com: best guess record for domain of bigeasy@linutronix.de designates 2a0a:51c0:0:12e:550::1 as permitted sender) client-ip=2a0a:51c0:0:12e:550::1; Authentication-Results: mx.google.com; spf=pass (google.com: best guess record for domain of bigeasy@linutronix.de designates 2a0a:51c0:0:12e:550::1 as permitted sender) smtp.mailfrom=bigeasy@linutronix.de Received: from bigeasy by Galois.linutronix.de with local (Exim 4.80) (envelope-from ) id 1hlFib-0006vw-V3; Wed, 10 Jul 2019 18:45:21 +0200 Date: Wed, 10 Jul 2019 18:45:21 +0200 From: Sebastian Andrzej Siewior To: Dave Hansen Cc: linux-mm@kvack.org, tglx@linutronix.de Subject: Re: Memory compaction and mlockall() Message-ID: <20190710164521.vlcrrfovphd5fp7f@linutronix.de> References: <20190710144138.qyn4tuttdq6h7kqx@linutronix.de> <66785c4b-b1cc-7b5a-a756-041068e3bec6@intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <66785c4b-b1cc-7b5a-a756-041068e3bec6@intel.com> User-Agent: NeoMutt/20180716 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 2019-07-10 09:20:47 [-0700], Dave Hansen wrote: > On 7/10/19 7:41 AM, Sebastian Andrzej Siewior wrote: > > I did not expect a pagefault with mlockall(). I assume it has to do with > > memory compaction. > > mlock() doesn't technically prevent faults. From the manpage: > > > mlock(), mlock2(), and mlockall() lock part or all of the > > calling process's virtual address space into RAM, preventing that > > memory from being paged to the swap area. > I read that as basically saying there will be no major faults, but minor > faults are possible. It says "lock virtual address space into into RAM". I assumed that there will be no page faults because everything is locked. The problem (besides the delay caused by the context switch and fix up) is that a major fault (with might have happened at the same time in another thread) will block this minor fault even longer. Sebastian