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=-2.2 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 AA978C433DF for ; Tue, 7 Jul 2020 03:51:22 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 835572078B for ; Tue, 7 Jul 2020 03:51:22 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728262AbgGGDvV (ORCPT ); Mon, 6 Jul 2020 23:51:21 -0400 Received: from foss.arm.com ([217.140.110.172]:42876 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725941AbgGGDvU (ORCPT ); Mon, 6 Jul 2020 23:51:20 -0400 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 90E72C0A; Mon, 6 Jul 2020 20:51:19 -0700 (PDT) Received: from [10.163.86.118] (unknown [10.163.86.118]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id E34973F718; Mon, 6 Jul 2020 20:51:11 -0700 (PDT) Subject: Re: [PATCH V4 1/3] mm/sparsemem: Enable vmem_altmap support in vmemmap_populate_basepages() To: David Hildenbrand , linux-mm@kvack.org Cc: justin.he@arm.com, catalin.marinas@arm.com, akpm@linux-foundation.org, Will Deacon , Mark Rutland , Paul Walmsley , Palmer Dabbelt , Tony Luck , Fenghua Yu , Dave Hansen , Andy Lutomirski , Peter Zijlstra , Thomas Gleixner , Ingo Molnar , Mike Rapoport , Michal Hocko , "Matthew Wilcox (Oracle)" , "Kirill A. Shutemov" , Dan Williams , Pavel Tatashin , linux-arm-kernel@lists.infradead.org, linux-ia64@vger.kernel.org, linux-riscv@lists.infradead.org, x86@kernel.org, linux-kernel@vger.kernel.org References: <1594004178-8861-1-git-send-email-anshuman.khandual@arm.com> <1594004178-8861-2-git-send-email-anshuman.khandual@arm.com> From: Anshuman Khandual Message-ID: <7ac5ff78-378c-37e2-444f-9f72844b8697@arm.com> Date: Tue, 7 Jul 2020 09:20:52 +0530 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.9.1 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 07/06/2020 02:33 PM, David Hildenbrand wrote: >> return 0; >> @@ -1505,7 +1505,7 @@ int __meminit vmemmap_populate(unsigned long start, unsigned long end, int node, >> int err; >> >> if (end - start < PAGES_PER_SECTION * sizeof(struct page)) >> - err = vmemmap_populate_basepages(start, end, node); >> + err = vmemmap_populate_basepages(start, end, node, NULL); >> else if (boot_cpu_has(X86_FEATURE_PSE)) >> err = vmemmap_populate_hugepages(start, end, node, altmap); >> else if (altmap) { > > It's somewhat weird that we don't allocate basepages from altmap on x86 > (both for sub-sections and without PSE). I wonder if we can simply > unlock that with your change. Especially, also handle the > !X86_FEATURE_PSE case below properly with an altmap. > > a) all hw with PMEM has PSE - except special QEMU setups, so nobody > cared to implement. For the sub-section special case, nobody cared about > a handfull of memmap not ending up on the altmap. (but it's still wasted > system memory IIRC). > > b) the pagetable overhead for small pages is not-neglectable and might > result in similar issues as solved by the switch to altmap on very huge > PMEM (with small amount of system RAM). > > I guess it is due to a). Hmm, I assume these are some decisions that x86 platform will have to make going forward in a subsequent patch as the third patch does for the arm64 platform. But it is clearly beyond the scope of this patch which never intended to change existing behavior on a given platform. > > [...] > >> >> -pte_t * __meminit vmemmap_pte_populate(pmd_t *pmd, unsigned long addr, int node) >> +pte_t * __meminit vmemmap_pte_populate(pmd_t *pmd, unsigned long addr, int node, >> + struct vmem_altmap *altmap) >> { >> pte_t *pte = pte_offset_kernel(pmd, addr); >> if (pte_none(*pte)) { >> pte_t entry; >> - void *p = vmemmap_alloc_block_buf(PAGE_SIZE, node); >> + void *p; >> + >> + if (altmap) >> + p = altmap_alloc_block_buf(PAGE_SIZE, altmap); >> + else >> + p = vmemmap_alloc_block_buf(PAGE_SIZE, node); >> if (!p) >> return NULL; > > I was wondering if > > if (altmap) > p = altmap_alloc_block_buf(PAGE_SIZE, altmap); > if (!p) > p = vmemmap_alloc_block_buf(PAGE_SIZE, node); > if (!p) > return NULL > > Would make sense. But I guess this isn't really relevant in practice, > because the altmap is usually sized properly. > > In general, LGTM. Okay, I assume that no further changes are required here.