From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx163.postini.com [74.125.245.163]) by kanga.kvack.org (Postfix) with SMTP id EF0FA6B0069 for ; Wed, 30 May 2012 16:02:01 -0400 (EDT) Received: by qcsd16 with SMTP id d16so145061qcs.14 for ; Wed, 30 May 2012 13:02:01 -0700 (PDT) Date: Wed, 30 May 2012 16:01:51 -0400 From: Konrad Rzeszutek Wilk Subject: Re: [PATCH 04/35] autonuma: define _PAGE_NUMA_PTE and _PAGE_NUMA_PMD Message-ID: <20120530200150.GA30148@localhost.localdomain> References: <1337965359-29725-1-git-send-email-aarcange@redhat.com> <1337965359-29725-5-git-send-email-aarcange@redhat.com> <20120530182247.GA28341@localhost.localdomain> <20120530183406.GH21339@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20120530183406.GH21339@redhat.com> Sender: owner-linux-mm@kvack.org List-ID: To: Andrea Arcangeli Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org, Hillf Danton , Dan Smith , Peter Zijlstra , Linus Torvalds , Andrew Morton , Thomas Gleixner , Ingo Molnar , Paul Turner , Suresh Siddha , Mike Galbraith , "Paul E. McKenney" , Lai Jiangshan , Bharata B Rao , Lee Schermerhorn , Rik van Riel , Johannes Weiner , Srivatsa Vaddagiri , Christoph Lameter On Wed, May 30, 2012 at 08:34:06PM +0200, Andrea Arcangeli wrote: > Hi Konrad, > > On Wed, May 30, 2012 at 02:22:49PM -0400, Konrad Rzeszutek Wilk wrote: > > Thank you for loking at this from the xen side. The interesting thing > > is that I believe the _PAGE_PAT (or _PAGE_PSE) is actually used on > > Xen on PTEs. It is used to mark the pages WC. > > Oops, I'm using _PAGE_PSE too on the pte, but only when it's unmapped. > > static inline int pte_numa(pte_t pte) > { > return (pte_flags(pte) & > (_PAGE_NUMA_PTE|_PAGE_PRESENT)) == _PAGE_NUMA_PTE; > } > > And _PAGE_UNUSED2 (_PAGE_IOMAP) is used for the pmd but _PAGE_IOMAP by > Xen should only be set on ptes. > > The only way to use _PAGE_PSE safe on the pte is if the pte is > non-present, is this what Xen is also doing? (in turn colliding with > pte_numa) The only time the _PAGE_PSE (_PAGE_PAT) is set is when _PAGE_PCD | _PAGE_PWT are set. It is this ugly transformation of doing: if (pat_enabled && _PAGE_PWT | _PAGE_PCD) pte = ~(_PAGE_PWT | _PAGE_PCD) | _PAGE_PAT; and then writting the pte with the 7th bit set instead of the 2nd and 3rd to mark it as WC. There is a corresponding reverse too (to read the pte - so the pte_val calls) - so if _PAGE_PAT is detected it will remove the _PAGE_PAT and return the PTE as if it had _PAGE_PWT | _PAGE_PCD. So that little bit of code will need some tweaking - as it does that even if _PAGE_PRESENT is not set. Meaning it would transform your _PAGE_PAT to _PAGE_PWT | _PAGE_PCD. Gah! > > Now if I shrink the size of the page_autonuma to one entry per pmd > (instead of per pte) I may as well drop pte_numa entirely and only > leave pmd_numa. At the moment it's possible to switch between the two > models at runtime with sysctl (if one wants to do a more expensive > granular tracking). I'm still uncertain on the best way to shrink > the page_autonuma size we'll see. OK. I can whip up a patch to deal with the 'Gah!' case easily if needed. Thanks! -- 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/ . Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/ Don't email: email@kvack.org