From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-1.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 6C7FFC43387 for ; Mon, 14 Jan 2019 04:01:07 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 42C1320657 for ; Mon, 14 Jan 2019 04:01:07 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726751AbfANEBF (ORCPT ); Sun, 13 Jan 2019 23:01:05 -0500 Received: from foss.arm.com ([217.140.101.70]:54318 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726697AbfANEBF (ORCPT ); Sun, 13 Jan 2019 23:01:05 -0500 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.72.51.249]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 7078780D; Sun, 13 Jan 2019 20:01:04 -0800 (PST) Received: from [10.162.42.129] (p8cg001049571a15.blr.arm.com [10.162.42.129]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 2C24C3F5BD; Sun, 13 Jan 2019 20:00:54 -0800 (PST) Subject: Re: [PATCH] mm: Introduce GFP_PGTABLE To: Michal Hocko Cc: 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@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 References: <1547288798-10243-1-git-send-email-anshuman.khandual@arm.com> <20190113173555.GC1578@dhcp22.suse.cz> From: Anshuman Khandual Message-ID: Date: Mon, 14 Jan 2019 09:30:55 +0530 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.9.1 MIME-Version: 1.0 In-Reply-To: <20190113173555.GC1578@dhcp22.suse.cz> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 01/13/2019 11:05 PM, Michal Hocko wrote: > On Sat 12-01-19 15:56:38, 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. > > I agree that some unification is due but GFP_PGTABLE is not something to > expose in generic gfp.h IMHO. It just risks an abuse. I would be looking Why would you think that it risks an abuse ? It does not create new semantics of allocation in the buddy. Its just uses existing GFP_KERNEL allocation which is then getting zeroed out. The risks (if any) is exactly same as GFP_KERNEL. > at providing asm-generic implementation and reuse it to remove the code Does that mean GFP_PGTABLE can be created but not in gfp.h but in some other memory related header file ? > duplication. But I haven't tried that to know that it will work out due > to small/subtle differences between arches. IIUC from the allocation perspective GFP_ACCOUNT is the only thing which gets added with GFP_PGTABLE for user page table for memcg accounting purpose. There does not seem to be any other differences unless I am missing something.