From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-yk0-f170.google.com (mail-yk0-f170.google.com [209.85.160.170]) by kanga.kvack.org (Postfix) with ESMTP id 67CE26B003A for ; Tue, 30 Sep 2014 13:11:41 -0400 (EDT) Received: by mail-yk0-f170.google.com with SMTP id 20so1142895yks.29 for ; Tue, 30 Sep 2014 10:11:41 -0700 (PDT) Received: from g4t3426.houston.hp.com (g4t3426.houston.hp.com. [15.201.208.54]) by mx.google.com with ESMTPS id v23si16517776yha.104.2014.09.30.10.11.40 for (version=TLSv1 cipher=RC4-SHA bits=128/128); Tue, 30 Sep 2014 10:11:40 -0700 (PDT) From: "Zuckerman, Boris" Subject: RE: [PATCH v11 00/21] Add support for NV-DIMMs to ext4 Date: Tue, 30 Sep 2014 17:10:26 +0000 Message-ID: <4C30833E5CDF444D84D942543DF65BDA6E047B9B@G4W3303.americas.hpqcorp.net> References: <1411677218-29146-1-git-send-email-matthew.r.wilcox@intel.com> <15705.1412070301@turing-police.cc.vt.edu> <20140930144854.GA5098@wil.cx> <123795.1412088827@turing-police.cc.vt.edu> <20140930160841.GB5098@wil.cx> In-Reply-To: <20140930160841.GB5098@wil.cx> Content-Language: en-US Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: quoted-printable MIME-Version: 1.0 Sender: owner-linux-mm@kvack.org List-ID: To: Matthew Wilcox , "Valdis.Kletnieks@vt.edu" Cc: Matthew Wilcox , "linux-fsdevel@vger.kernel.org" , "linux-mm@kvack.org" , "linux-kernel@vger.kernel.org" >=20 > The more I think about this, the more I think this is a bad idea. > When you have a file open with O_DIRECT, your I/O has to be done in 512-b= yte > multiples, and it has to be aligned to 512-byte boundaries in memory. If= an > unsuspecting application has O_DIRECT forced on it, it isn't going to kno= w to do that, > and so all its I/Os will fail. > It'll also be horribly inefficient if a program has the file mmaped. >=20 > What problem are you really trying to solve? Some big files hogging the = page cache? > -- Page cache? As another copy in RAM?=20 NV_DIMMs may be viewed as a caching device. This caching can be implemented= on the level of NV block/offset or may have some hints from FS and applica= tions. Temporary files is one example. They may not need to hit NV domain e= ver. Some transactional journals or DB files is another example. They may s= tay in RAM until power off. -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org