From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-ed1-f71.google.com (mail-ed1-f71.google.com [209.85.208.71]) by kanga.kvack.org (Postfix) with ESMTP id 1157D8E0002 for ; Wed, 16 Jan 2019 08:27:28 -0500 (EST) Received: by mail-ed1-f71.google.com with SMTP id c18so2314194edt.23 for ; Wed, 16 Jan 2019 05:27:28 -0800 (PST) Received: from foss.arm.com (usa-sjc-mx-foss1.foss.arm.com. [217.140.101.70]) by mx.google.com with ESMTP id m18-v6si3218118ejq.276.2019.01.16.05.27.26 for ; Wed, 16 Jan 2019 05:27:26 -0800 (PST) Subject: Re: [PATCH V2] mm: Introduce GFP_PGTABLE References: <1547619692-7946-1-git-send-email-anshuman.khandual@arm.com> <20190116065703.GE24149@dhcp22.suse.cz> <20190116123018.GF6310@bombadil.infradead.org> <20190116124431.GK24149@dhcp22.suse.cz> From: Anshuman Khandual Message-ID: Date: Wed, 16 Jan 2019 18:57:13 +0530 MIME-Version: 1.0 In-Reply-To: <20190116124431.GK24149@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 , Matthew Wilcox 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-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 01/16/2019 06:14 PM, Michal Hocko wrote: > 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. Fair enough. So we seem to have agreement over __GFP_ACCOUNT for user page tables but not for the kernel. But should we accommodate __GFP_RETRY_MAYFAIL or drop them altogether (including multi order allocation requests) ?