From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751150AbdGZIxc (ORCPT ); Wed, 26 Jul 2017 04:53:32 -0400 Received: from mx2.suse.de ([195.135.220.15]:34799 "EHLO mx1.suse.de" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1750813AbdGZIxa (ORCPT ); Wed, 26 Jul 2017 04:53:30 -0400 Date: Wed, 26 Jul 2017 10:53:25 +0200 From: Michal Hocko To: Punit Agrawal Cc: Andrew Morton , Naoya Horiguchi , linux-mm@kvack.org, linux-kernel@vger.kernel.org, linux-arch@vger.kernel.org, steve.capper@arm.com, will.deacon@arm.com, catalin.marinas@arm.com, kirill.shutemov@linux.intel.com, Mike Kravetz Subject: Re: [PATCH 1/1] mm/hugetlb: Make huge_pte_offset() consistent and document behaviour Message-ID: <20170726085325.GC2981@dhcp22.suse.cz> References: <20170725154114.24131-1-punit.agrawal@arm.com> <20170725154114.24131-2-punit.agrawal@arm.com> <20170726085038.GB2981@dhcp22.suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20170726085038.GB2981@dhcp22.suse.cz> 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 On Wed 26-07-17 10:50:38, Michal Hocko wrote: > On Tue 25-07-17 16:41:14, Punit Agrawal wrote: > > When walking the page tables to resolve an address that points to > > !p*d_present() entry, huge_pte_offset() returns inconsistent values > > depending on the level of page table (PUD or PMD). > > > > It returns NULL in the case of a PUD entry while in the case of a PMD > > entry, it returns a pointer to the page table entry. > > > > A similar inconsitency exists when handling swap entries - returns NULL > > for a PUD entry while a pointer to the pte_t is retured for the PMD > > entry. > > > > Update huge_pte_offset() to make the behaviour consistent - return NULL > > in the case of p*d_none() and a pointer to the pte_t for hugepage or > > swap entries. > > > > Document the behaviour to clarify the expected behaviour of this > > function. This is to set clear semantics for architecture specific > > implementations of huge_pte_offset(). > > hugetlb pte semantic is a disaster and I agree it could see some > cleanup/clarifications but I am quite nervous to see a patchi like this. > How do we check that nothing will get silently broken by this change? Forgot to add. Hugetlb have been special because of the pte sharing. I haven't looked into that code for quite some time but there might be a good reason why pud behave differently. -- Michal Hocko SUSE Labs From mboxrd@z Thu Jan 1 00:00:00 1970 From: Michal Hocko Subject: Re: [PATCH 1/1] mm/hugetlb: Make huge_pte_offset() consistent and document behaviour Date: Wed, 26 Jul 2017 10:53:25 +0200 Message-ID: <20170726085325.GC2981@dhcp22.suse.cz> References: <20170725154114.24131-1-punit.agrawal@arm.com> <20170725154114.24131-2-punit.agrawal@arm.com> <20170726085038.GB2981@dhcp22.suse.cz> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Content-Disposition: inline In-Reply-To: <20170726085038.GB2981@dhcp22.suse.cz> Sender: owner-linux-mm@kvack.org To: Punit Agrawal Cc: Andrew Morton , Naoya Horiguchi , linux-mm@kvack.org, linux-kernel@vger.kernel.org, linux-arch@vger.kernel.org, steve.capper@arm.com, will.deacon@arm.com, catalin.marinas@arm.com, kirill.shutemov@linux.intel.com, Mike Kravetz List-Id: linux-arch.vger.kernel.org On Wed 26-07-17 10:50:38, Michal Hocko wrote: > On Tue 25-07-17 16:41:14, Punit Agrawal wrote: > > When walking the page tables to resolve an address that points to > > !p*d_present() entry, huge_pte_offset() returns inconsistent values > > depending on the level of page table (PUD or PMD). > > > > It returns NULL in the case of a PUD entry while in the case of a PMD > > entry, it returns a pointer to the page table entry. > > > > A similar inconsitency exists when handling swap entries - returns NULL > > for a PUD entry while a pointer to the pte_t is retured for the PMD > > entry. > > > > Update huge_pte_offset() to make the behaviour consistent - return NULL > > in the case of p*d_none() and a pointer to the pte_t for hugepage or > > swap entries. > > > > Document the behaviour to clarify the expected behaviour of this > > function. This is to set clear semantics for architecture specific > > implementations of huge_pte_offset(). > > hugetlb pte semantic is a disaster and I agree it could see some > cleanup/clarifications but I am quite nervous to see a patchi like this. > How do we check that nothing will get silently broken by this change? Forgot to add. Hugetlb have been special because of the pte sharing. I haven't looked into that code for quite some time but there might be a good reason why pud behave differently. -- Michal Hocko SUSE Labs -- 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