From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pd0-f173.google.com (mail-pd0-f173.google.com [209.85.192.173]) by kanga.kvack.org (Postfix) with ESMTP id BA8026B0035 for ; Tue, 30 Sep 2014 12:08:57 -0400 (EDT) Received: by mail-pd0-f173.google.com with SMTP id g10so2071022pdj.18 for ; Tue, 30 Sep 2014 09:08:57 -0700 (PDT) Received: from mga03.intel.com (mga03.intel.com. [134.134.136.65]) by mx.google.com with ESMTP id na4si27134312pbc.235.2014.09.30.09.08.56 for ; Tue, 30 Sep 2014 09:08:56 -0700 (PDT) Date: Tue, 30 Sep 2014 12:08:41 -0400 From: Matthew Wilcox Subject: Re: [PATCH v11 00/21] Add support for NV-DIMMs to ext4 Message-ID: <20140930160841.GB5098@wil.cx> 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> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <123795.1412088827@turing-police.cc.vt.edu> Sender: owner-linux-mm@kvack.org List-ID: To: Valdis.Kletnieks@vt.edu Cc: Matthew Wilcox , Matthew Wilcox , linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org On Tue, Sep 30, 2014 at 10:53:47AM -0400, Valdis.Kletnieks@vt.edu wrote: > On Tue, 30 Sep 2014 10:48:54 -0400, Matthew Wilcox said: > > > No, it doesn't try to do that. Wouldn't you be better served with an > > LD_PRELOAD that forces O_DIRECT on? > > Not when you don't want it on every file, and users are creating and > deleting files once in a while. A chattr-like command is easier and > more scalable than rebuilding the LD_PRELOAD every time the list of > files gets changed.... 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-byte 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 know to do that, and so all its I/Os will fail. It'll also be horribly inefficient if a program has the file mmaped. What problem are you really trying to solve? Some big files hogging the page cache? -- 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