From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755181Ab2ITMoa (ORCPT ); Thu, 20 Sep 2012 08:44:30 -0400 Received: from cam-admin0.cambridge.arm.com ([217.140.96.50]:60687 "EHLO cam-admin0.cambridge.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754658Ab2ITMo2 (ORCPT ); Thu, 20 Sep 2012 08:44:28 -0400 Date: Thu, 20 Sep 2012 13:44:01 +0100 From: Will Deacon To: Ralf Baechle Cc: Catalin Marinas , Andrew Morton , "linux-mm@kvack.org" , "linux-kernel@vger.kernel.org" , "linux-arch@vger.kernel.org" , "mhocko@suse.cz" , Steve Capper Subject: Re: [PATCH 2/3] mm: thp: Fix the update_mmu_cache() last argument passing in mm/huge_memory.c Message-ID: <20120920124401.GF4654@mudshark.cambridge.arm.com> References: <1347382036-18455-1-git-send-email-will.deacon@arm.com> <1347382036-18455-3-git-send-email-will.deacon@arm.com> <20120915133833.GA32398@linux-mips.org> <20120918123331.6ca5833c.akpm@linux-foundation.org> <20120919155346.GB32398@linux-mips.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20120919155346.GB32398@linux-mips.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 Hi Ralf, On Wed, Sep 19, 2012 at 04:53:46PM +0100, Ralf Baechle wrote: > On Wed, Sep 19, 2012 at 10:12:28AM +0100, Catalin Marinas wrote: > > > >> 5) void update_mmu_cache(struct vm_area_struct *vma, > > >> unsigned long address, pte_t *ptep) > > > > > > Yes please. > > > > Should we just use a generic (void *) for the last argument or force a > > cast in mm/huge_memory.c? > > > > Ralf's point is that transparent huge page code calls update_mmu_cache > > with a (pmd_t *) as the last argument. This could make sense for THP > > as it assumes that huge pages can only be created at the pmd level. > > But that's unlike mm/hugetlb.c which casts huge page types to pte_t, > > even though on ARM they are implemented at the pmd level. > > > > On ARM (with VIPT caches) update_mmu_cache() is empty like on x86, > > though a static inline rather than macro. > > It's even worse - mm/huge_memory.c is passing a pmd_t, not a pointer so > changing the type of update_mmu_cache's 3rd argument alone won't cut it. > > This went unnoticed so far because all existing architectures supporting > transparent huge pages implement update_mmu_cache() as do { } while (0). > > MIPS uses update_mmu_cache() as the hook to deal with cache aliases and > pre-faulting a TLB entry. But aliases don't affect small pages and having > a separate variant of update_mmu_cache for huge pages will allow some other > optimizations. That's minor but it's the argument types that really need > to be fixed and because MIPS also implements huge pages at PMD level I'd > be happy if we settle on pte_t * for mm/huge_memory.c. Just to clarify: do you want a cast from pmd_t * to pte_t * or instead copy the hugetlb code and pass ptes around instead of pmds? The latter is pretty invasive... Will