From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-ed1-f70.google.com (mail-ed1-f70.google.com [209.85.208.70]) by kanga.kvack.org (Postfix) with ESMTP id 1EDE06B000E for ; Tue, 7 Aug 2018 07:52:13 -0400 (EDT) Received: by mail-ed1-f70.google.com with SMTP id d18-v6so5304396edp.0 for ; Tue, 07 Aug 2018 04:52:13 -0700 (PDT) Received: from mx1.suse.de (mx2.suse.de. [195.135.220.15]) by mx.google.com with ESMTPS id v25-v6si1674152edb.343.2018.08.07.04.52.11 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Tue, 07 Aug 2018 04:52:11 -0700 (PDT) Subject: Re: [PATCH v2] resource: Merge resources on a node when hot-adding memory References: <20180806065224.31383-1-rashmica.g@gmail.com> From: Vlastimil Babka Message-ID: <5543a32a-20f9-18ff-dc13-73737257ed99@suse.cz> Date: Tue, 7 Aug 2018 13:52:07 +0200 MIME-Version: 1.0 In-Reply-To: <20180806065224.31383-1-rashmica.g@gmail.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: Rashmica Gupta , toshi.kani@hpe.com, tglx@linutronix.de, akpm@linux-foundation.org, bp@suse.de, brijesh.singh@amd.com, thomas.lendacky@amd.com, jglisse@redhat.com, gregkh@linuxfoundation.org, baiyaowei@cmss.chinamobile.com, dan.j.williams@intel.com, mhocko@suse.com, iamjoonsoo.kim@lge.com, malat@debian.org, pasha.tatashin@oracle.com, bhelgaas@google.com, osalvador@techadventures.net, yasu.isimatu@gmail.com, linux-kernel@vger.kernel.org, linux-mm@kvack.org On 08/06/2018 08:52 AM, Rashmica Gupta wrote: > When hot-removing memory release_mem_region_adjustable() splits > iomem resources if they are not the exact size of the memory being > hot-deleted. Adding this memory back to the kernel adds a new > resource. > > Eg a node has memory 0x0 - 0xfffffffff. Offlining and hot-removing > 1GB from 0xf40000000 results in the single resource 0x0-0xfffffffff being > split into two resources: 0x0-0xf3fffffff and 0xf80000000-0xfffffffff. > > When we hot-add the memory back we now have three resources: > 0x0-0xf3fffffff, 0xf40000000-0xf7fffffff, and 0xf80000000-0xfffffffff. > > Now if we try to remove a section of memory that overlaps these resources, > like 2GB from 0xf40000000, release_mem_region_adjustable() fails as it > expects the chunk of memory to be within the boundaries of a single > resource. Hi, it's the first time I see the resource code, so I might be easily wrong. How can it happen that the second remove is section aligned but the first one not? > This patch adds a function request_resource_and_merge(). This is called > instead of request_resource_conflict() when registering a resource in > add_memory(). It calls request_resource_conflict() and if hot-removing is > enabled (if it isn't we won't get resource fragmentation) we attempt to > merge contiguous resources on the node. > > Signed-off-by: Rashmica Gupta ... > --- a/kernel/resource.c > +++ b/kernel/resource.c ... > +/* > + * Attempt to merge resources on the node > + */ > +static void merge_node_resources(int nid, struct resource *parent) > +{ > + struct resource *res; > + uint64_t start_addr; > + uint64_t end_addr; > + int ret; > + > + start_addr = node_start_pfn(nid) << PAGE_SHIFT; > + end_addr = node_end_pfn(nid) << PAGE_SHIFT; > + > + write_lock(&resource_lock); > + > + /* Get the first resource */ > + res = parent->child; > + > + while (res) { > + /* Check that the resource is within the node */ > + if (res->start < start_addr) { > + res = res->sibling; > + continue; > + } > + /* Exit if resource is past end of node */ > + if (res->sibling->end > end_addr) > + break; IIUC, resource end is closed, so adjacent resources's start is end+1. But node_end_pfn is open, so the comparison above should use '>=' instead of '>'? > + > + ret = merge_resources(res); > + if (!ret) > + continue; > + res = res->sibling; Should this rather use next_resource() to merge at all levels of the hierarchy? Although memory seems to be flat under &iomem_resource so it would be just future-proofing. Thanks, Vlastimil