Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753473AbbF2OwL (ORCPT ); Mon, 29 Jun 2015 10:52:11 -0400 Received: from mail-qk0-f176.google.com ([209.85.220.176]:36559 "EHLO mail-qk0-f176.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752634AbbF2OvA (ORCPT ); Mon, 29 Jun 2015 10:51:00 -0400 Date: Mon, 29 Jun 2015 10:50:54 -0400 From: Jerome Glisse To: Mark Hairgrove Cc: "akpm@linux-foundation.org" , "linux-kernel@vger.kernel.org" , "linux-mm@kvack.org" , Linus Torvalds , "joro@8bytes.org" , Mel Gorman , "H. Peter Anvin" , Peter Zijlstra , Andrea Arcangeli , Johannes Weiner , Larry Woodman , Rik van Riel , Dave Airlie , Brendan Conoboy , Joe Donohue , Duncan Poole , Sherry Cheung , Subhash Gutti , John Hubbard , Lucien Dunning , Cameron Buschardt , Arvind Gopalakrishnan , Haggai Eran , Shachar Raindel , Liran Liss , Roland Dreier , Ben Sander , Greg Stoner , John Bridgman , Michael Mantor , Paul Blinzer , Laurent Morichetti , Alexander Deucher , Oded Gabbay , =?iso-8859-1?B?Suly9G1l?= Glisse , Jatin Kumar Subject: Re: [PATCH 07/36] HMM: add per mirror page table v3. Message-ID: <20150629145053.GB2173@gmail.com> References: <1432236705-4209-1-git-send-email-j.glisse@gmail.com> <1432236705-4209-8-git-send-email-j.glisse@gmail.com> <20150626164338.GB3748@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: User-Agent: Mutt/1.5.23 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2523 Lines: 54 On Fri, Jun 26, 2015 at 08:02:03PM -0700, Mark Hairgrove wrote: > On Fri, 26 Jun 2015, Jerome Glisse wrote: > > On Thu, Jun 25, 2015 at 04:05:48PM -0700, Mark Hairgrove wrote: > > > On Thu, 21 May 2015, j.glisse@gmail.com wrote: > > > > From: J?r?me Glisse > > > > [...] > > > > > > > > + /* update() - update device mmu following an event. > > > > + * > > > > + * @mirror: The mirror that link process address space with the device. > > > > + * @event: The event that triggered the update. > > > > + * Returns: 0 on success or error code {-EIO, -ENOMEM}. > > > > + * > > > > + * Called to update device page table for a range of address. > > > > + * The event type provide the nature of the update : > > > > + * - Range is no longer valid (munmap). > > > > + * - Range protection changes (mprotect, COW, ...). > > > > + * - Range is unmapped (swap, reclaim, page migration, ...). > > > > + * - Device page fault. > > > > + * - ... > > > > + * > > > > + * Thought most device driver only need to use pte_mask as it reflects > > > > + * change that will happen to the HMM page table ie : > > > > + * new_pte = old_pte & event->pte_mask; > > > > > > Documentation request: It would be useful to break down exactly what is > > > required from the driver for each event type here, and what extra > > > information is provided by the type that isn't provided by the pte_mask. > > > > Mostly event tell you if you need to free or not the device page table for > > the range, which is not something you can infer from the pte_mask reliably. > > Difference btw migration and munmap for instance, same pte_mask but range > > is still valid in the migration case it will just be backed by a new set of > > pages. > > Given that event->pte_mask and event->type provide redundant information, > are they both necessary? Like said, you can not infer event->type from pte_mask but you can infer pte_mask from event->type. The idea is behind providing pte_mask is that simple driver can just use that with the iter walk and simply mask the HMM page table entry they read ((*ptep) & pte_mask) to repopulate the device page table. So yes pte_mask is redundant but i think it will be useful for a range of device driver. Cheers, J?r?me -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/