From mboxrd@z Thu Jan 1 00:00:00 1970 From: Matthew Wilcox Subject: Re: [PATCH v2 1/3] arm64: mm: use appropriate ctors for page tables Date: Wed, 20 Feb 2019 04:24:18 -0800 Message-ID: <20190220122418.GE12668@bombadil.infradead.org> References: <20190214211642.2200-1-yuzhao@google.com> <20190218231319.178224-1-yuzhao@google.com> <863acc9a-53fb-86ad-4521-828ee8d9c222@arm.com> <20190219053205.GA124985@google.com> <8f9b0bfb-b787-fa3e-7322-73a56a618aa8@arm.com> <20190219222828.GA68281@google.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Content-Disposition: inline In-Reply-To: Sender: linux-kernel-owner@vger.kernel.org To: Anshuman Khandual Cc: Yu Zhao , 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 Wed, Feb 20, 2019 at 03:57:59PM +0530, Anshuman Khandual wrote: > On 02/20/2019 03:58 AM, Yu Zhao wrote: > > On Tue, Feb 19, 2019 at 11:47:12AM +0530, Anshuman Khandual wrote: > >> On 02/19/2019 11:02 AM, Yu Zhao wrote: > >>> 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 think the commit is the following one and it does say so. But what is > >> the rationale of tagging only PTE page as PageTable and updating the zone > >> stat but not doing so for higher level page table pages ? Are not they > >> used as page table pages ? Should not they count towards NR_PAGETABLE ? > >> > >> 1d40a5ea01d53251c ("mm: mark pages in use for page tables") > > > > Well, I was just trying to clarify how the ctor is meant to be used. > > The rational behind it is probably another topic. > > > > For starters, the number of pmd/pud/p4d/pgd is at least two orders > > of magnitude less than the number of pte, which makes them almost > > negligible. And some archs use kmem for them, so it's infeasible to > > SetPageTable on or account them in the way the ctor does on those > > archs. > > I understand the kmem cases which are definitely problematic and should > be fixed. IIRC there is a mechanism to custom init pages allocated for > slab cache with a ctor function which in turn can call pgtable_page_ctor(). > But destructor helper support for slab has been dropped I guess. You can't put a spinlock in the struct page if the page is allocated through slab. Slab uses basically all of struct page for its own purposes. I tried to make that clear with the new layout of struct page where everything's in a union discriminated by what the page is allocated for. From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from bombadil.infradead.org ([198.137.202.133]:39878 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725881AbfBTMYZ (ORCPT ); Wed, 20 Feb 2019 07:24:25 -0500 Date: Wed, 20 Feb 2019 04:24:18 -0800 From: Matthew Wilcox Subject: Re: [PATCH v2 1/3] arm64: mm: use appropriate ctors for page tables Message-ID: <20190220122418.GE12668@bombadil.infradead.org> References: <20190214211642.2200-1-yuzhao@google.com> <20190218231319.178224-1-yuzhao@google.com> <863acc9a-53fb-86ad-4521-828ee8d9c222@arm.com> <20190219053205.GA124985@google.com> <8f9b0bfb-b787-fa3e-7322-73a56a618aa8@arm.com> <20190219222828.GA68281@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Sender: linux-arch-owner@vger.kernel.org List-ID: To: Anshuman Khandual Cc: Yu Zhao , 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: <20190220122418.gBPHmAGz9bF9FSLvdfsbCL9iPeJ7f0cg7K0Ru0YsxrM@z> On Wed, Feb 20, 2019 at 03:57:59PM +0530, Anshuman Khandual wrote: > On 02/20/2019 03:58 AM, Yu Zhao wrote: > > On Tue, Feb 19, 2019 at 11:47:12AM +0530, Anshuman Khandual wrote: > >> On 02/19/2019 11:02 AM, Yu Zhao wrote: > >>> 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 think the commit is the following one and it does say so. But what is > >> the rationale of tagging only PTE page as PageTable and updating the zone > >> stat but not doing so for higher level page table pages ? Are not they > >> used as page table pages ? Should not they count towards NR_PAGETABLE ? > >> > >> 1d40a5ea01d53251c ("mm: mark pages in use for page tables") > > > > Well, I was just trying to clarify how the ctor is meant to be used. > > The rational behind it is probably another topic. > > > > For starters, the number of pmd/pud/p4d/pgd is at least two orders > > of magnitude less than the number of pte, which makes them almost > > negligible. And some archs use kmem for them, so it's infeasible to > > SetPageTable on or account them in the way the ctor does on those > > archs. > > I understand the kmem cases which are definitely problematic and should > be fixed. IIRC there is a mechanism to custom init pages allocated for > slab cache with a ctor function which in turn can call pgtable_page_ctor(). > But destructor helper support for slab has been dropped I guess. You can't put a spinlock in the struct page if the page is allocated through slab. Slab uses basically all of struct page for its own purposes. I tried to make that clear with the new layout of struct page where everything's in a union discriminated by what the page is allocated for.