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=-3.6 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,MAILING_LIST_MULTI,SPF_PASS,USER_AGENT_MUTT 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 1FC59C43444 for ; Wed, 16 Jan 2019 12:44:42 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id E4F2020657 for ; Wed, 16 Jan 2019 12:44:41 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1547642682; bh=POdIZ2yOuysxpHyx96Jdas1VKPgBc4oYmnmFiLg4HfQ=; h=Date:From:To:Cc:Subject:References:In-Reply-To:List-ID:From; b=DQAMlbGE2rvfEN1mAVSdny9QLB8qm6HM+Fz0dK7QYTsgiMuYAp+O6BfUdmq76br/q G3qCxB4APkR7ZOjRA8M8Pn4OSFXb00oshyccliRKXmpxIYSNU4KJVZaNteOUqkUHCF FATnM917VervjXK6JmonC8SnFTMoqdKvBpV6DBy8= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2392815AbfAPMok (ORCPT ); Wed, 16 Jan 2019 07:44:40 -0500 Received: from mx2.suse.de ([195.135.220.15]:37738 "EHLO mx1.suse.de" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1732803AbfAPMoj (ORCPT ); Wed, 16 Jan 2019 07:44:39 -0500 X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.220.254]) by mx1.suse.de (Postfix) with ESMTP id C0897AED6; Wed, 16 Jan 2019 12:44:37 +0000 (UTC) Date: Wed, 16 Jan 2019 13:44:31 +0100 From: Michal Hocko 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 Subject: Re: [PATCH V2] mm: Introduce GFP_PGTABLE Message-ID: <20190116124431.GK24149@dhcp22.suse.cz> References: <1547619692-7946-1-git-send-email-anshuman.khandual@arm.com> <20190116065703.GE24149@dhcp22.suse.cz> <20190116123018.GF6310@bombadil.infradead.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190116123018.GF6310@bombadil.infradead.org> User-Agent: Mutt/1.10.1 (2018-07-13) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed 16-01-19 04:30:18, 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. Yes, I believe the only reason this is x86 only is that each arch would have to be tweaked separately. So a cleanup in _that_ regard would be helpful. There is no real reason to have ptes accounted only for x86. There might be some exceptions but well, our asm-generic allows to opt in for generic implementation or override it with a special one. The later should be an exception rather than the rule. -- Michal Hocko SUSE Labs