From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751864AbaEUEeI (ORCPT ); Wed, 21 May 2014 00:34:08 -0400 Received: from mail-pd0-f173.google.com ([209.85.192.173]:44348 "EHLO mail-pd0-f173.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751831AbaEUEeG (ORCPT ); Wed, 21 May 2014 00:34:06 -0400 Date: Tue, 20 May 2014 21:32:47 -0700 (PDT) From: Hugh Dickins X-X-Sender: hugh@eggly.anvils To: Kenny Simpson cc: "Kirill A. Shutemov" , "Kirill A. Shutemov" , Michal Hocko , linux-kernel@vger.kernel.org, Andrew Morton , Peter Zijlstra , Dave Jones , Linus Torvalds , Armin Rigo Subject: Re: remap_file_pages() use In-Reply-To: Message-ID: References: <20140519130114.GA3140@dhcp22.suse.cz> <20140519143540.BE9F6E009B@blue.fi.intel.com> <20140519212416.GA14152@node.dhcp.inet.fi> User-Agent: Alpine 2.11 (LSU 23 2013-08-11) MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, 20 May 2014, Kenny Simpson wrote: > I might need a gentle nudge with a clue stick... > checking against latest git tree it looks as though most common > filesystem types do support remap_file_pages. > > I just wrote a simple test case and it worked on my 3.13-based ubuntu > 14.04 system on an ext4 filesystem. It is all very confusing, yes. When Kirill said disk-backed files don't support remap_file_pages since commit 3ee6dafc677a, he was meaning that that they do not support it with a special nonlinear vma; but the remap_file_pages syscall emulates the layout for them with separate linear vmas instead. Confusingly, these filesystems opt in to this emulation by pointing their remap_pages method to generic_file_remap_pages - code which is then never used for them! tmpfs is the only filesystem (having no page_mkwrite) which actually passes through that code. You can understand why there's some enthusiasm for cleaning this up :) Hugh