From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932221Ab2ISPyC (ORCPT ); Wed, 19 Sep 2012 11:54:02 -0400 Received: from eddie.linux-mips.org ([78.24.191.182]:44579 "EHLO cvs.linux-mips.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755658Ab2ISPyA (ORCPT ); Wed, 19 Sep 2012 11:54:00 -0400 Date: Wed, 19 Sep 2012 17:53:46 +0200 From: Ralf Baechle To: Catalin Marinas Cc: Andrew Morton , Will Deacon , 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: <20120919155346.GB32398@linux-mips.org> 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> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: 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 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. Ralf