From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pg1-f199.google.com (mail-pg1-f199.google.com [209.85.215.199]) by kanga.kvack.org (Postfix) with ESMTP id BA8F88E0002 for ; Thu, 17 Jan 2019 04:56:43 -0500 (EST) Received: by mail-pg1-f199.google.com with SMTP id p4so5796492pgj.21 for ; Thu, 17 Jan 2019 01:56:43 -0800 (PST) Received: from ozlabs.org (ozlabs.org. [2401:3900:2:1::2]) by mx.google.com with ESMTPS id 1si1278170plp.114.2019.01.17.01.56.41 for (version=TLS1_2 cipher=ECDHE-RSA-CHACHA20-POLY1305 bits=256/256); Thu, 17 Jan 2019 01:56:42 -0800 (PST) From: Michael Ellerman Subject: Re: [PATCH V2] mm: Introduce GFP_PGTABLE In-Reply-To: <20190116123018.GF6310@bombadil.infradead.org> References: <1547619692-7946-1-git-send-email-anshuman.khandual@arm.com> <20190116065703.GE24149@dhcp22.suse.cz> <20190116123018.GF6310@bombadil.infradead.org> Date: Thu, 17 Jan 2019 20:56:34 +1100 Message-ID: <87tvi74nfx.fsf@concordia.ellerman.id.au> MIME-Version: 1.0 Content-Type: text/plain Sender: owner-linux-mm@kvack.org List-ID: To: Matthew Wilcox , Michal Hocko 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, 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 Matthew Wilcox writes: > 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. powerpc does __GFP_ACCOUNT for user page tables too. Shamelessly cribbed from the x86 version of course :) cheers