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=-14.8 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI,NICE_REPLY_A, SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_SANE_1 autolearn=ham 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 9CE91C433E2 for ; Thu, 10 Sep 2020 06:46:04 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 5058220720 for ; Thu, 10 Sep 2020 06:46:04 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727791AbgIJGqD (ORCPT ); Thu, 10 Sep 2020 02:46:03 -0400 Received: from foss.arm.com ([217.140.110.172]:55528 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726228AbgIJGqB (ORCPT ); Thu, 10 Sep 2020 02:46:01 -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 5A78731B; Wed, 9 Sep 2020 23:46:00 -0700 (PDT) Received: from [10.163.71.250] (unknown [10.163.71.250]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 663D33F66E; Wed, 9 Sep 2020 23:45:57 -0700 (PDT) Subject: Re: [PATCH] arm64/mm: add fallback option to allocate virtually contiguous memory To: Sudarshan Rajagopalan , linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org Cc: Catalin Marinas , Will Deacon , Mark Rutland , Logan Gunthorpe , David Hildenbrand , Andrew Morton , Steven Price References: <01010174769e2b68-a6f3768e-aef8-43c7-b357-a8cb1e17d3eb-000000@us-west-2.amazonses.com> From: Anshuman Khandual Message-ID: <0475e813-cb95-0992-39e4-593bfd5cdbf8@arm.com> Date: Thu, 10 Sep 2020 12:15:25 +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: <01010174769e2b68-a6f3768e-aef8-43c7-b357-a8cb1e17d3eb-000000@us-west-2.amazonses.com> 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 Hello Sudarshan, On 09/10/2020 11:35 AM, Sudarshan Rajagopalan wrote: > When section mappings are enabled, we allocate vmemmap pages from physically > continuous memory of size PMD_SZIE using vmemmap_alloc_block_buf(). Section> mappings are good to reduce TLB pressure. But when system is highly fragmented > and memory blocks are being hot-added at runtime, its possible that such > physically continuous memory allocations can fail. Rather than failing the Did you really see this happen on a system ? > memory hot-add procedure, add a fallback option to allocate vmemmap pages from > discontinuous pages using vmemmap_populate_basepages(). Which could lead to a mixed page size mapping in the VMEMMAP area. Allocation failure in vmemmap_populate() should just cleanly fail the memory hot add operation, which can then be retried. Why the retry has to be offloaded to kernel ? > > Signed-off-by: Sudarshan Rajagopalan > Cc: Catalin Marinas > Cc: Will Deacon > Cc: Anshuman Khandual > Cc: Mark Rutland > Cc: Logan Gunthorpe > Cc: David Hildenbrand > Cc: Andrew Morton > Cc: Steven Price > --- > arch/arm64/mm/mmu.c | 15 ++++++++++++--- > 1 file changed, 12 insertions(+), 3 deletions(-) > > diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c > index 75df62f..a46c7d4 100644 > --- a/arch/arm64/mm/mmu.c > +++ b/arch/arm64/mm/mmu.c > @@ -1100,6 +1100,7 @@ int __meminit vmemmap_populate(unsigned long start, unsigned long end, int node, > p4d_t *p4dp; > pud_t *pudp; > pmd_t *pmdp; > + int ret = 0; > > do { > next = pmd_addr_end(addr, end); > @@ -1121,15 +1122,23 @@ int __meminit vmemmap_populate(unsigned long start, unsigned long end, int node, > void *p = NULL; > > p = vmemmap_alloc_block_buf(PMD_SIZE, node, altmap); > - if (!p) > - return -ENOMEM; > + if (!p) { > +#ifdef CONFIG_MEMORY_HOTPLUG > + vmemmap_free(start, end, altmap); > +#endif The mapping was never created in the first place, as the allocation failed. vmemmap_free() here will free an unmapped area ! > + ret = -ENOMEM; > + break; > + } > > pmd_set_huge(pmdp, __pa(p), __pgprot(PROT_SECT_NORMAL)); > } else > vmemmap_verify((pte_t *)pmdp, node, addr, next); > } while (addr = next, addr != end); > > - return 0; > + if (ret) > + return vmemmap_populate_basepages(start, end, node, altmap); > + else > + return ret; > } > #endif /* !ARM64_SWAPPER_USES_SECTION_MAPS */ > void vmemmap_free(unsigned long start, unsigned long end, >