From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-ed1-f70.google.com (mail-ed1-f70.google.com [209.85.208.70]) by kanga.kvack.org (Postfix) with ESMTP id 7618D8E0002 for ; Sun, 13 Jan 2019 23:01:07 -0500 (EST) Received: by mail-ed1-f70.google.com with SMTP id b7so8431688eda.10 for ; Sun, 13 Jan 2019 20:01:07 -0800 (PST) Received: from foss.arm.com (foss.arm.com. [217.140.101.70]) by mx.google.com with ESMTP id c21si1794670edt.291.2019.01.13.20.01.05 for ; Sun, 13 Jan 2019 20:01:05 -0800 (PST) Subject: Re: [PATCH] mm: Introduce GFP_PGTABLE 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 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: owner-linux-mm@kvack.org List-ID: 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 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.