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[66.63.167.143]) by mx.google.com with ESMTPS id b18si5167947ywh.298.2019.03.12.08.46.53 for (version=TLS1_2 cipher=ECDHE-RSA-CHACHA20-POLY1305 bits=256/256); Tue, 12 Mar 2019 08:46:54 -0700 (PDT) Received-SPF: pass (google.com: domain of james.bottomley@hansenpartnership.com designates 66.63.167.143 as permitted sender) client-ip=66.63.167.143; Authentication-Results: mx.google.com; dkim=pass header.i=@hansenpartnership.com header.s=20151216 header.b=Hta5ADB6; spf=pass (google.com: domain of james.bottomley@hansenpartnership.com designates 66.63.167.143 as permitted sender) smtp.mailfrom=James.Bottomley@hansenpartnership.com; dmarc=pass (p=NONE sp=NONE dis=NONE) header.from=hansenpartnership.com Received: from localhost (localhost [127.0.0.1]) by bedivere.hansenpartnership.com (Postfix) with ESMTP id 6B8298EE1ED; Tue, 12 Mar 2019 08:46:52 -0700 (PDT) Received: from bedivere.hansenpartnership.com ([127.0.0.1]) by localhost (bedivere.hansenpartnership.com [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id xRUipMi-5v4r; Tue, 12 Mar 2019 08:46:52 -0700 (PDT) Received: from [153.66.254.194] (unknown [50.35.68.20]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by bedivere.hansenpartnership.com (Postfix) with ESMTPSA id ACA718EE0F5; Tue, 12 Mar 2019 08:46:51 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=simple/simple; d=hansenpartnership.com; s=20151216; t=1552405612; bh=rtBt5DLADL8t5XJ0aWEYYr4qVgiTJN0Y03AmnFBmALQ=; h=Subject:From:To:Cc:Date:In-Reply-To:References:From; b=Hta5ADB6diO123b+O9GGsaD3lTLmZxm0/SklZjxqjxFxREBbKMqH2pQq9KC9TpqUY FtBLt58elI9vQLiHqAfSyBBJn+aScF4ecBuiM54tPSDYp7m2jwOVqEwLyHHPM9lpUr kiGaEaRYtHEEndxKTdxFwSggNcuYAAt4p59ArUEw= Message-ID: <1552405610.3083.17.camel@HansenPartnership.com> Subject: Re: [RFC PATCH V2 0/5] vhost: accelerate metadata access through vmap() From: James Bottomley To: "Michael S. Tsirkin" , Jason Wang Cc: David Miller , hch@infradead.org, kvm@vger.kernel.org, virtualization@lists.linux-foundation.org, netdev@vger.kernel.org, linux-kernel@vger.kernel.org, peterx@redhat.com, linux-mm@kvack.org, aarcange@redhat.com, linux-arm-kernel@lists.infradead.org, linux-parisc@vger.kernel.org Date: Tue, 12 Mar 2019 08:46:50 -0700 In-Reply-To: <20190312075033-mutt-send-email-mst@kernel.org> References: <20190308141220.GA21082@infradead.org> <56374231-7ba7-0227-8d6d-4d968d71b4d6@redhat.com> <20190311095405-mutt-send-email-mst@kernel.org> <20190311.111413.1140896328197448401.davem@davemloft.net> <6b6dcc4a-2f08-ba67-0423-35787f3b966c@redhat.com> <20190311235140-mutt-send-email-mst@kernel.org> <76c353ed-d6de-99a9-76f9-f258074c1462@redhat.com> <20190312075033-mutt-send-email-mst@kernel.org> Content-Type: text/plain; charset="UTF-8" X-Mailer: Evolution 3.26.6 Mime-Version: 1.0 Content-Transfer-Encoding: 8bit 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, 2019-03-12 at 07:54 -0400, Michael S. Tsirkin wrote: > On Tue, Mar 12, 2019 at 03:17:00PM +0800, Jason Wang wrote: > > > > On 2019/3/12 上午11:52, Michael S. Tsirkin wrote: > > > On Tue, Mar 12, 2019 at 10:59:09AM +0800, Jason Wang wrote: [...] > > At least for -stable, we need the flush? > > > > > > > Three atomic ops per bit is way to expensive. > > > > > > Yes. > > > > Thanks > > See James's reply - I stand corrected we do kunmap so no need to > flush. Well, I said that's what we do on Parisc. The cachetlb document definitely says if you alter the data between kmap and kunmap you are responsible for the flush. It's just that flush_dcache_page() is a no- op on x86 so they never remember to add it and since it will crash parisc if you get it wrong we finally gave up trying to make them. But that's the point: it is a no-op on your favourite architecture so it costs you nothing to add it. James