From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-ed1-f72.google.com (mail-ed1-f72.google.com [209.85.208.72]) by kanga.kvack.org (Postfix) with ESMTP id 8DFAE8E0002 for ; Wed, 16 Jan 2019 08:33:07 -0500 (EST) Received: by mail-ed1-f72.google.com with SMTP id t2so2345501edb.22 for ; Wed, 16 Jan 2019 05:33:07 -0800 (PST) Received: from mx1.suse.de (mx2.suse.de. [195.135.220.15]) by mx.google.com with ESMTPS id n6-v6si4175981ejy.72.2019.01.16.05.33.06 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Wed, 16 Jan 2019 05:33:06 -0800 (PST) Date: Wed, 16 Jan 2019 14:33:02 +0100 From: Michal Hocko Subject: Re: [PATCH V2] mm: Introduce GFP_PGTABLE Message-ID: <20190116133302.GN24149@dhcp22.suse.cz> References: <1547619692-7946-1-git-send-email-anshuman.khandual@arm.com> <20190116065703.GE24149@dhcp22.suse.cz> <20190116123018.GF6310@bombadil.infradead.org> <07d6a264-dccd-78ab-e8a9-2410bbef7b97@arm.com> <20190116131827.GH6310@bombadil.infradead.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190116131827.GH6310@bombadil.infradead.org> Sender: owner-linux-mm@kvack.org List-ID: To: Matthew Wilcox Cc: Anshuman Khandual , linux-mm@kvack.org, akpm@linux-foundation.org, linux-kernel@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, linux-arm-kernel@lists.infradead.org, linux-sh@vger.kernel.org, kvmarm@lists.cs.columbia.edu, linux-riscv@lists.infradead.org, linux@armlinux.org.uk, catalin.marinas@arm.com, will.deacon@arm.com, mpe@ellerman.id.au, tglx@linutronix.de, mingo@redhat.com, dave.hansen@linux.intel.com, peterz@infradead.org, christoffer.dall@arm.com, marc.zyngier@arm.com, kirill@shutemov.name, rppt@linux.vnet.ibm.com, ard.biesheuvel@linaro.org, mark.rutland@arm.com, steve.capper@arm.com, james.morse@arm.com, robin.murphy@arm.com, aneesh.kumar@linux.ibm.com, vbabka@suse.cz, shakeelb@google.com, rientjes@google.com, palmer@sifive.com, greentime@andestech.com On Wed 16-01-19 05:18:27, Matthew Wilcox wrote: > On Wed, Jan 16, 2019 at 06:42:22PM +0530, Anshuman Khandual wrote: > > On 01/16/2019 06:00 PM, Matthew Wilcox wrote: > > > On Wed, Jan 16, 2019 at 07:57:03AM +0100, Michal Hocko wrote: > > >> On Wed 16-01-19 11:51:32, Anshuman Khandual wrote: > > >>> All architectures have been defining their own PGALLOC_GFP as (GFP_KERNEL | > > >>> __GFP_ZERO) and using it for allocating page table pages. This causes some > > >>> code duplication which can be easily avoided. GFP_KERNEL allocated and > > >>> cleared out pages (__GFP_ZERO) are required for page tables on any given > > >>> architecture. This creates a new generic GFP flag flag which can be used > > >>> for any page table page allocation. Does not cause any functional change. > > >>> > > >>> GFP_PGTABLE is being added into include/asm-generic/pgtable.h which is the > > >>> generic page tabe header just to prevent it's potential misuse as a general > > >>> allocation flag if included in include/linux/gfp.h. > > >> > > >> I haven't reviewed the patch yet but I am wondering whether this is > > >> really worth it without going all the way down to unify the common code > > >> and remove much more code duplication. Or is this not possible for some > > >> reason? > > > > > > Exactly what I suggested doing in response to v1. > > > > > > Also, the approach taken here is crazy. x86 has a feature that no other > > > architecture has bothered to implement yet -- accounting page tables > > > to the process. Yet instead of spreading that goodness to all other > > > architectures, Anshuman has gone to more effort to avoid doing that. > > > > The basic objective for this patch is to create a common minimum allocation > > flag that can be used by architectures but that still allows archs to add > > on additional constraints if they see fit. This patch does not intend to > > change functionality for any arch. > > I disagree with your objective. Making more code common is a great idea, > but this patch is too unambitious. We should be heading towards one or > two page table allocation functions instead of having every architecture do > its own thing. > > So start there. Move the x86 function into common code and convert one > other architecture to use it too. Agreed! -- Michal Hocko SUSE Labs