From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-ve0-f174.google.com (mail-ve0-f174.google.com [209.85.128.174]) by kanga.kvack.org (Postfix) with ESMTP id 5D18D6B014C for ; Tue, 18 Mar 2014 22:57:01 -0400 (EDT) Received: by mail-ve0-f174.google.com with SMTP id oz11so7947823veb.5 for ; Tue, 18 Mar 2014 19:57:01 -0700 (PDT) Received: from mail-ve0-x22f.google.com (mail-ve0-x22f.google.com [2607:f8b0:400c:c01::22f]) by mx.google.com with ESMTPS id w5si7200661vcl.141.2014.03.18.19.57.00 for (version=TLSv1 cipher=ECDHE-RSA-RC4-SHA bits=128/128); Tue, 18 Mar 2014 19:57:00 -0700 (PDT) Received: by mail-ve0-f175.google.com with SMTP id oz11so8135869veb.34 for ; Tue, 18 Mar 2014 19:57:00 -0700 (PDT) MIME-Version: 1.0 In-Reply-To: References: <20140311045109.GB12551@redhat.com> <20140310220158.7e8b7f2a.akpm@linux-foundation.org> <20140311053017.GB14329@redhat.com> <20140311132024.GC32390@moon> <531F0E39.9020100@oracle.com> <20140311134158.GD32390@moon> <20140311142817.GA26517@redhat.com> <20140311143750.GE32390@moon> <20140311171045.GA4693@redhat.com> <20140311173603.GG32390@moon> <20140311173917.GB4693@redhat.com> Date: Tue, 18 Mar 2014 19:57:00 -0700 Message-ID: Subject: Re: bad rss-counter message in 3.14rc5 From: Linus Torvalds Content-Type: text/plain; charset=UTF-8 Sender: owner-linux-mm@kvack.org List-ID: To: Hugh Dickins Cc: Dave Jones , Cyrill Gorcunov , Sasha Levin , Andrew Morton , Linux Kernel , linux-mm , Joonsoo Kim , Bob Liu , Konstantin Khlebnikov On Tue, Mar 18, 2014 at 7:37 PM, Hugh Dickins wrote: > > For 3.15, and probably 3.16 too, we should keep in place whatever > partial accommodations we have for the case (such as allowing for > anon and swap in fremap's zap_pte), in case we do need to revert; > but clean those away later on. (Not many, I think: it was mainly > a guilty secret that VM accounting didn't really hold together.) Absolutely. See if it works to just stop doing that special COW, and then later on, if we have decided "nobody even noticed", we can remove the hacks we have to support the fact that shared mappings sometimes have anon pages in them. > :) That fits with what I heard of HP-UX mmap, > but I never had the pleasure of dealing with it. They had purely virtually indexed caches, making coherency "interesting". Together with a VM based on some really old BSD VM code that everybody else had thrown out, and that didn't allow you to unmap things partially etc. So HPUX mmap really didn't work, not even for non-shared mmap's. I think they fixed the interfaces in HP-UX 11. But not being coherent meant that the shared mappings tended to still have trouble. nntp largely died, but was replaced with the cyrus imapd that played similar games. At least out mmap was always coherent. Even in MAP_PRIVATE, and with regards to both write() system calls and other mmap PROT_WRITE users. Except when we had bugs. Shared mmap really isn't very simple to get right. Linus -- 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