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Tue, 10 Dec 2019 11:25:51 +0000 (UTC) Received: from [10.36.117.222] (ovpn-117-222.ams2.redhat.com [10.36.117.222]) by smtp.corp.redhat.com (Postfix) with ESMTP id 24CDF1084196; Tue, 10 Dec 2019 11:25:46 +0000 (UTC) Subject: Re: [PATCH 5/6] mm, memory_hotplug: Provide argument for the pgprot_t in arch_add_memory() To: Michal Hocko Cc: Dan Williams , Logan Gunthorpe , Linux Kernel Mailing List , Linux ARM , linux-ia64@vger.kernel.org, linuxppc-dev , linux-s390 , Linux-sh , platform-driver-x86@vger.kernel.org, Linux MM , Christoph Hellwig , Andrew Morton , Catalin Marinas , Will Deacon , Benjamin Herrenschmidt , Thomas Gleixner , Ingo Molnar , Borislav Petkov , Dave Hansen , Andy Lutomirski , Peter Zijlstra References: <20191209191346.5197-1-logang@deltatee.com> <20191209191346.5197-6-logang@deltatee.com> <20191210100432.GC10404@dhcp22.suse.cz> <6da2b279-6a6d-d89c-a34c-962ed021d91d@redhat.com> <20191210103452.GF10404@dhcp22.suse.cz> From: David Hildenbrand Autocrypt: addr=david@redhat.com; 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Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.1.1 MIME-Version: 1.0 In-Reply-To: <20191210103452.GF10404@dhcp22.suse.cz> Content-Language: en-US X-Scanned-By: MIMEDefang 2.84 on 10.5.11.22 X-MC-Unique: I1kxIsanPWW9ImTAvoKXeg-1 X-Mimecast-Spam-Score: 0 Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 10.12.19 11:34, Michal Hocko wrote: > On Tue 10-12-19 11:09:46, David Hildenbrand wrote: >> On 10.12.19 11:04, Michal Hocko wrote: >>> On Mon 09-12-19 12:43:40, Dan Williams wrote: >>>> On Mon, Dec 9, 2019 at 12:24 PM Logan Gunthorpe wrote: >>>>> >>>>> >>>>> >>>>> On 2019-12-09 12:23 p.m., David Hildenbrand wrote: >>>>>> On 09.12.19 20:13, Logan Gunthorpe wrote: >>> [...] >>>>>>> #ifdef CONFIG_MEMORY_HOTPLUG >>>>>>> -int arch_add_memory(int nid, u64 start, u64 size, >>>>>>> +int arch_add_memory(int nid, u64 start, u64 size, pgprot_t prot, >>>>>>> struct mhp_restrictions *restrictions) >>>>>> >>>>>> Can we fiddle that into "struct mhp_restrictions" instead? >>>>> >>>>> Yes, if that's what people want, it's pretty trivial to do. I chose not >>>>> to do it that way because it doesn't get passed down to add_pages() and >>>>> it's not really a "restriction". If I don't hear any objections, I will >>>>> do that for v2. >>>> >>>> +1 to storing this information alongside the altmap in that structure. >>>> However, I agree struct mhp_restrictions, with the MHP_MEMBLOCK_API >>>> flag now gone, has lost all of its "restrictions". How about dropping >>>> the 'flags' property and renaming the struct to 'struct >>>> mhp_modifiers'? >>> >>> Hmm, this email somehow didn't end up in my inbox so I have missed it >>> before replying. >>> >>> Well, mhp_modifiers makes some sense and it would reduce the API >>> proliferation but how do you expect the prot part to be handled? >>> I really do not want people to think about PAGE_KERNEL or which >>> protection to use because my experience tells that this will get copied >>> without much thinking or simply will break with some odd usecases. >>> So how exactly this would be used? >> >> I was thinking about exactly the same "issue". >> >> 1. default initialization via a function >> >> memhp_modifier_default_init(&modified); >> >> 2. a flag that unlocks the prot field (default:0). Without the flag, it >> is ignored. We can keep the current initialization then. >> >> Other ideas? > > 3. a prot mask to apply on top of PAGE_KERNEL? Or would that be > insufficient/clumsy? > If it works for the given use case, I guess this would be simple and ok. -- Thanks, David / dhildenb