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=-2.5 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=no 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 4F5EEC5ACAE for ; Wed, 11 Sep 2019 10:31:56 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 1273D222C1 for ; Wed, 11 Sep 2019 10:31:56 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 1273D222C1 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=redhat.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id 9DE5D6B0005; Wed, 11 Sep 2019 06:31:55 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 9901C6B0006; 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Wed, 11 Sep 2019 10:31:53 +0000 (UTC) Received: from [10.36.117.155] (ovpn-117-155.ams2.redhat.com [10.36.117.155]) by smtp.corp.redhat.com (Postfix) with ESMTP id BA1F25D6A5; Wed, 11 Sep 2019 10:31:48 +0000 (UTC) Subject: Re: [PATCH V7 3/3] arm64/mm: Enable memory hot remove To: Catalin Marinas , Anshuman Khandual Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, akpm@linux-foundation.org, will@kernel.org, mark.rutland@arm.com, mhocko@suse.com, ira.weiny@intel.com, cai@lca.pw, logang@deltatee.com, cpandya@codeaurora.org, arunks@codeaurora.org, dan.j.williams@intel.com, mgorman@techsingularity.net, osalvador@suse.de, ard.biesheuvel@arm.com, steve.capper@arm.com, broonie@kernel.org, valentin.schneider@arm.com, Robin.Murphy@arm.com, steven.price@arm.com, suzuki.poulose@arm.com References: <1567503958-25831-1-git-send-email-anshuman.khandual@arm.com> <1567503958-25831-4-git-send-email-anshuman.khandual@arm.com> <20190910161759.GI14442@C02TF0J2HF1T.local> From: David Hildenbrand Openpgp: preference=signencrypt Autocrypt: addr=david@redhat.com; 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Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.8.0 MIME-Version: 1.0 In-Reply-To: <20190910161759.GI14442@C02TF0J2HF1T.local> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit X-Scanned-By: MIMEDefang 2.79 on 10.5.11.15 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.6.2 (mx1.redhat.com [10.5.110.62]); Wed, 11 Sep 2019 10:31:53 +0000 (UTC) X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On 10.09.19 18:17, Catalin Marinas wrote: > On Tue, Sep 03, 2019 at 03:15:58PM +0530, Anshuman Khandual wrote: >> @@ -770,6 +1022,28 @@ int __meminit vmemmap_populate(unsigned long start, unsigned long end, int node, >> void vmemmap_free(unsigned long start, unsigned long end, >> struct vmem_altmap *altmap) >> { >> +#ifdef CONFIG_MEMORY_HOTPLUG >> + /* >> + * FIXME: We should have called remove_pagetable(start, end, true). >> + * vmemmap and vmalloc virtual range might share intermediate kernel >> + * page table entries. Removing vmemmap range page table pages here >> + * can potentially conflict with a concurrent vmalloc() allocation. >> + * >> + * This is primarily because vmalloc() does not take init_mm ptl for >> + * the entire page table walk and it's modification. Instead it just >> + * takes the lock while allocating and installing page table pages >> + * via [p4d|pud|pmd|pte]_alloc(). A concurrently vanishing page table >> + * entry via memory hot remove can cause vmalloc() kernel page table >> + * walk pointers to be invalid on the fly which can cause corruption >> + * or worst, a crash. >> + * >> + * So free_empty_tables() gets called where vmalloc and vmemmap range >> + * do not overlap at any intermediate level kernel page table entry. >> + */ >> + unmap_hotplug_range(start, end, true); >> + if (!vmalloc_vmemmap_overlap) >> + free_empty_tables(start, end); >> +#endif >> } >> #endif /* CONFIG_SPARSEMEM_VMEMMAP */ > > I wonder whether we could simply ignore the vmemmap freeing altogether, > just leave it around and not unmap it. This way, we could call > unmap_kernel_range() for removing the linear map and we save some code. > > For the linear map, I think we use just above 2MB of tables for 1GB of > memory mapped (worst case with 4KB pages we need 512 pte pages). For > vmemmap we'd use slightly above 2MB for a 64GB hotplugged memory. Do we > expect such memory to be re-plugged again in the same range? If we do, > then I shouldn't even bother with removing the vmmemmap. > FWIW, I think we should do it cleanly. > I don't fully understand the use-case for memory hotremove, so any > additional info would be useful to make a decision here. > Especially in virtual environment, hotremove will be relevant. For physical environments - I have no idea how important that is for ARM. -- Thanks, David / dhildenb