From mboxrd@z Thu Jan 1 00:00:00 1970 From: Yu Zhao Subject: Re: [PATCH v2 1/3] arm64: mm: use appropriate ctors for page tables Date: Mon, 18 Feb 2019 22:32:05 -0700 Message-ID: <20190219053205.GA124985@google.com> References: <20190214211642.2200-1-yuzhao@google.com> <20190218231319.178224-1-yuzhao@google.com> <863acc9a-53fb-86ad-4521-828ee8d9c222@arm.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Content-Disposition: inline In-Reply-To: <863acc9a-53fb-86ad-4521-828ee8d9c222@arm.com> Sender: linux-kernel-owner@vger.kernel.org To: Anshuman Khandual Cc: Catalin Marinas , Will Deacon , "Aneesh Kumar K . V" , Andrew Morton , Nick Piggin , Peter Zijlstra , Joel Fernandes , "Kirill A . Shutemov" , Mark Rutland , Ard Biesheuvel , Chintan Pandya , Jun Yao , Laura Abbott , linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, linux-arch@vger.kernel.org, linux-mm@kvack.org List-Id: linux-arch.vger.kernel.org On Tue, Feb 19, 2019 at 09:51:01AM +0530, Anshuman Khandual wrote: > > > On 02/19/2019 04:43 AM, Yu Zhao wrote: > > For pte page, use pgtable_page_ctor(); for pmd page, use > > pgtable_pmd_page_ctor() if not folded; and for the rest (pud, > > p4d and pgd), don't use any. > pgtable_page_ctor()/dtor() is not optional for any level page table page > as it determines the struct page state and zone statistics. This is not true. pgtable_page_ctor() is only meant for user pte page. The name isn't perfect (we named it this way before we had split pmd page table lock, and never bothered to change it). The commit cccd843f54be ("mm: mark pages in use for page tables") clearly states so: Note that only pages currently accounted as NR_PAGETABLES are tracked as PageTable; this does not include pgd/p4d/pud/pmd pages. I'm sure if we go back further, we can find similar stories: we don't set PageTable on page tables other than pte; and we don't account page tables other than pte. I don't have any objection if you want change these two. But please make sure they are consistent across all archs. > We should not skip it for any page table page. In fact, calling it on pmd/pud/p4d is peculiar, and may even be considered wrong. AFAIK, no other arch does so. > As stated before pgtable_pmd_page_ctor() is not a replacement for > pgtable_page_ctor(). pgtable_pmd_page_ctor() must be used on user pmd. For kernel pmd, it's okay to use pgtable_page_ctor() instead only because kernel doesn't have thp. From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-it1-f193.google.com ([209.85.166.193]:38956 "EHLO mail-it1-f193.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725765AbfBSFcJ (ORCPT ); Tue, 19 Feb 2019 00:32:09 -0500 Received: by mail-it1-f193.google.com with SMTP id l15so3441556iti.4 for ; Mon, 18 Feb 2019 21:32:08 -0800 (PST) Date: Mon, 18 Feb 2019 22:32:05 -0700 From: Yu Zhao Subject: Re: [PATCH v2 1/3] arm64: mm: use appropriate ctors for page tables Message-ID: <20190219053205.GA124985@google.com> References: <20190214211642.2200-1-yuzhao@google.com> <20190218231319.178224-1-yuzhao@google.com> <863acc9a-53fb-86ad-4521-828ee8d9c222@arm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <863acc9a-53fb-86ad-4521-828ee8d9c222@arm.com> Sender: linux-arch-owner@vger.kernel.org List-ID: To: Anshuman Khandual Cc: Catalin Marinas , Will Deacon , "Aneesh Kumar K . V" , Andrew Morton , Nick Piggin , Peter Zijlstra , Joel Fernandes , "Kirill A . Shutemov" , Mark Rutland , Ard Biesheuvel , Chintan Pandya , Jun Yao , Laura Abbott , linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, linux-arch@vger.kernel.org, linux-mm@kvack.org Message-ID: <20190219053205.HdhhV_eIl4WTP49LyBnbx2WeqOyb6g_QfBIj5iD12QY@z> On Tue, Feb 19, 2019 at 09:51:01AM +0530, Anshuman Khandual wrote: > > > On 02/19/2019 04:43 AM, Yu Zhao wrote: > > For pte page, use pgtable_page_ctor(); for pmd page, use > > pgtable_pmd_page_ctor() if not folded; and for the rest (pud, > > p4d and pgd), don't use any. > pgtable_page_ctor()/dtor() is not optional for any level page table page > as it determines the struct page state and zone statistics. This is not true. pgtable_page_ctor() is only meant for user pte page. The name isn't perfect (we named it this way before we had split pmd page table lock, and never bothered to change it). The commit cccd843f54be ("mm: mark pages in use for page tables") clearly states so: Note that only pages currently accounted as NR_PAGETABLES are tracked as PageTable; this does not include pgd/p4d/pud/pmd pages. I'm sure if we go back further, we can find similar stories: we don't set PageTable on page tables other than pte; and we don't account page tables other than pte. I don't have any objection if you want change these two. But please make sure they are consistent across all archs. > We should not skip it for any page table page. In fact, calling it on pmd/pud/p4d is peculiar, and may even be considered wrong. AFAIK, no other arch does so. > As stated before pgtable_pmd_page_ctor() is not a replacement for > pgtable_page_ctor(). pgtable_pmd_page_ctor() must be used on user pmd. For kernel pmd, it's okay to use pgtable_page_ctor() instead only because kernel doesn't have thp.