From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from [140.186.70.92] (port=35609 helo=eggs.gnu.org) by lists.gnu.org with esmtp (Exim 4.43) id 1PzQPn-00046A-OD for qemu-devel@nongnu.org; Tue, 15 Mar 2011 05:19:44 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1PzQPm-0003py-Kb for qemu-devel@nongnu.org; Tue, 15 Mar 2011 05:19:43 -0400 Received: from e23smtp08.au.ibm.com ([202.81.31.141]:35489) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1PzQPm-0003oy-4m for qemu-devel@nongnu.org; Tue, 15 Mar 2011 05:19:42 -0400 Received: from d23relay05.au.ibm.com (d23relay05.au.ibm.com [202.81.31.247]) by e23smtp08.au.ibm.com (8.14.4/8.13.1) with ESMTP id p2F9ELtQ001624 for ; Tue, 15 Mar 2011 20:14:21 +1100 Received: from d23av02.au.ibm.com (d23av02.au.ibm.com [9.190.235.138]) by d23relay05.au.ibm.com (8.13.8/8.13.8/NCO v10.0) with ESMTP id p2F9JRqE2183392 for ; Tue, 15 Mar 2011 20:19:28 +1100 Received: from d23av02.au.ibm.com (loopback [127.0.0.1]) by d23av02.au.ibm.com (8.14.4/8.13.1/NCO v10.0 AVout) with ESMTP id p2F9JRMv001631 for ; Tue, 15 Mar 2011 20:19:27 +1100 From: "Aneesh Kumar K. V" Subject: Re: [Qemu-devel] [PATCH -V3 7/8] hw/9pfs: Add new virtfs option cache=none to skip host page cache In-Reply-To: References: <1299347533-17047-1-git-send-email-aneesh.kumar@linux.vnet.ibm.com> <1299347533-17047-7-git-send-email-aneesh.kumar@linux.vnet.ibm.com> <87y64iq1tz.fsf@linux.vnet.ibm.com> Date: Tue, 15 Mar 2011 14:49:22 +0530 Message-ID: <87ipvkwxk5.fsf@linux.vnet.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable List-Id: qemu-devel.nongnu.org List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Stefan Hajnoczi Cc: aliguori@us.ibm.com, qemu-devel@nongnu.org On Mon, 14 Mar 2011 10:20:57 +0000, Stefan Hajnoczi wr= ote: > On Sun, Mar 13, 2011 at 7:04 PM, Aneesh Kumar K. V > wrote: > > On Sun, 13 Mar 2011 17:23:50 +0000, Stefan Hajnoczi wrote: > >> On Sat, Mar 5, 2011 at 5:52 PM, Aneesh Kumar K.V > >> wrote: > >> > cache=3Dnone implies the file are opened in the host with O_SYNC ope= n flag > >> > >> O_SYNC does not bypass the host page cache. =C2=A0It ensures that writ= es > >> only complete once data has been written to the disk. > >> > >> O_DIRECT is a hint to bypass the host page cache when possible. > >> > >> A boolean on|off option would be nicer than an option that takes the > >> special string "none". =C2=A0For example, direct=3Don|off. =C2=A0It al= so makes the > >> code nicer by using bools instead of strdup strings that get leaked. > >> > > > > What i wanted is the O_SYNC behavior. Well the comment should be update= d. I > > want to make sure that we don't have dirty data in host page cache after > > a write. It is always good to make read hit the page cache >=20 > Why silently enforce O_SYNC on the server side? The client does not > know whether or not O_SYNC is in effect, cannot take advantage of that > knowledge, and cannot control it. >=20 > I think a more useful solution is a 9p client mount option called > "sync" that caused the client to always add O_SYNC and skip syncfs. > The whole stack becomes aware of O_SYNC and clients are in control > over whether or not they need O_SYNC semantics. The cache=3Dnone specifically enables us to ignore the tsyncfs request on host. tsyncfs on host can be really slow in certain setup. -aneesh