From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751771AbcDZAla (ORCPT ); Mon, 25 Apr 2016 20:41:30 -0400 Received: from 216-12-86-13.cv.mvl.ntelos.net ([216.12.86.13]:57639 "EHLO brightrain.aerifal.cx" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750963AbcDZAl3 (ORCPT ); Mon, 25 Apr 2016 20:41:29 -0400 Date: Mon, 25 Apr 2016 20:41:24 -0400 From: Rich Felker To: Andrew Morton Cc: linux-kernel@vger.kernel.org, Michal Hocko , Greg Ungerer , Geert Uytterhoeven , Yoshinori Sato Subject: Re: [PATCH] tmpfs: fix VM_MAYSHARE mappings for NOMMU Message-ID: <20160426004124.GH21636@brightrain.aerifal.cx> References: <20160422221944.GA14264@brightrain.aerifal.cx> <20160425170909.31cf27c845a9fc19688fd5af@linux-foundation.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20160425170909.31cf27c845a9fc19688fd5af@linux-foundation.org> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Apr 25, 2016 at 05:09:09PM -0700, Andrew Morton wrote: > On Fri, 22 Apr 2016 18:19:44 -0400 Rich Felker wrote: > > > Subject: [PATCH] tmpfs: fix VM_MAYSHARE mappings for NOMMU > > I take it that "ramfs" was intended here. They're two names for the same thing; I'm not sure which should be preferred. Rich > > > The nommu do_mmap expects f_op->get_unmapped_area to either succeed or > > return -ENOSYS for VM_MAYSHARE (e.g. private read-only) mappings. > > Returning addr in the non-MAP_SHARED case was completely wrong, and > > only happened to work because addr was 0. However, it prevented > > VM_MAYSHARE mappings from sharing backing with the fs cache, and > > forced such mappings (including shareable program text) to be copied > > whenever the number of mappings transitioned from 0 to 1, impacting > > performance and memory usage. Subsequent mappings beyond the first > > still correctly shared memory with the first. > > > > Instead, treat VM_MAYSHARE identically to VM_SHARED at the file ops > > level; do_mmap already handles the semantic differences between them. > > > > ... > >