From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-wi0-f174.google.com (mail-wi0-f174.google.com [209.85.212.174]) by kanga.kvack.org (Postfix) with ESMTP id 0D3BB6B0253 for ; Mon, 10 Aug 2015 07:09:59 -0400 (EDT) Received: by wicja10 with SMTP id ja10so20544083wic.1 for ; Mon, 10 Aug 2015 04:09:58 -0700 (PDT) Received: from mail-wi0-f177.google.com (mail-wi0-f177.google.com. [209.85.212.177]) by mx.google.com with ESMTPS id b19si15553620wiw.16.2015.08.10.04.09.57 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Mon, 10 Aug 2015 04:09:57 -0700 (PDT) Received: by wicne3 with SMTP id ne3so17630441wic.0 for ; Mon, 10 Aug 2015 04:09:57 -0700 (PDT) Date: Mon, 10 Aug 2015 14:09:55 +0300 From: "Kirill A. Shutemov" Subject: Re: page-flags behavior on compound pages: a worry Message-ID: <20150810110955.GA27046@node.dhcp.inet.fi> References: <1426784902-125149-1-git-send-email-kirill.shutemov@linux.intel.com> <1426784902-125149-5-git-send-email-kirill.shutemov@linux.intel.com> <20150806153259.GA2834@node.dhcp.inet.fi> <20150807145056.GB12177@node.dhcp.inet.fi> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Sender: owner-linux-mm@kvack.org List-ID: To: Christoph Lameter Cc: Hugh Dickins , "Kirill A. Shutemov" , Andrew Morton , Andrea Arcangeli , David Rientjes , Dave Hansen , Mel Gorman , Rik van Riel , Vlastimil Babka , Naoya Horiguchi , Steve Capper , "Aneesh Kumar K.V" , Johannes Weiner , Michal Hocko , Jerome Marchand , linux-kernel@vger.kernel.org, linux-mm@kvack.org On Fri, Aug 07, 2015 at 10:28:49AM -0500, Christoph Lameter wrote: > On Fri, 7 Aug 2015, Kirill A. Shutemov wrote: > > > On Thu, Aug 06, 2015 at 03:45:31PM -0500, Christoph Lameter wrote: > > > On Thu, 6 Aug 2015, Hugh Dickins wrote: > > > > > > > > I know a patchset which solves this! ;) > > > > > > > > Oh, and I know a patchset which avoids these problems completely, > > > > by not using compound pages at all ;) > > > > > > Another dumb idea: Stop the insanity of splitting pages on the fly? > > > Splitting pages should work like page migration: Lock everything down and > > > ensure no one is using the page and then do it. That way the compound pages > > > and its metadata are as stable as a regular page. > > > > That's what I do in refcounting patchset. > > Looks like you make refcounting easier and avoid splitting in some cases > maybe only splitting the pmd. But the fundamental issue still remains. > Complexity is high since individual pages of a compound can be mapped and > unmapped in multiple processes. > > The compound would need to be always treated as a single order N entity > in order to really get things simplified and make code cleaner. > > Either all pages are mapped or none. Otherwise you have to manage the > a schizoprenic view of pages. Sometimes an order N size entity is > managed and sometimes a base page size page which is a fraction of the > whole. Such a view of a memory object is pretty difficult to manage. I don't see anything actionable here. Your wish list doesn't cope with reality. Compound pages are mapped with PTEs for almost ten years and I don't see why we should stop the practice. -- Kirill A. Shutemov -- 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