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[2003:cb:c70d:8300:4812:9d4f:6cd8:7f47]) by smtp.gmail.com with ESMTPSA id w6sm5136850wmi.15.2022.01.27.01.54.24 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 27 Jan 2022 01:54:24 -0800 (PST) Message-ID: <696b782f-0b50-9861-a34d-cf750d4244bd@redhat.com> Date: Thu, 27 Jan 2022 10:54:23 +0100 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.4.0 To: Jonghyeon Kim Cc: dan.j.williams@intel.com, vishal.l.verma@intel.com, dave.jiang@intel.com, akpm@linux-foundation.org, nvdimm@lists.linux.dev, linux-kernel@vger.kernel.org, linux-mm@kvack.org References: <20220126170002.19754-1-tome01@ajou.ac.kr> <5d02ea0e-aca6-a64b-23de-bc9307572d17@redhat.com> <20220127094142.GA31409@swarm08> From: David Hildenbrand Organization: Red Hat Subject: Re: [PATCH 1/2] mm/memory_hotplug: Export shrink span functions for zone and node In-Reply-To: <20220127094142.GA31409@swarm08> X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Language: en-US Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspamd-Queue-Id: 3A1ED40026 X-Rspam-User: nil Authentication-Results: imf17.hostedemail.com; dkim=pass header.d=redhat.com header.s=mimecast20190719 header.b=dxMikxzR; dmarc=pass (policy=none) header.from=redhat.com; spf=none (imf17.hostedemail.com: domain of david@redhat.com has no SPF policy when checking 170.10.129.124) smtp.mailfrom=david@redhat.com X-Stat-Signature: o57oq1fzrcj3jnzcxw44rzmgiax4woxb X-Rspamd-Server: rspam08 X-HE-Tag: 1643277268-684411 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 27.01.22 10:41, Jonghyeon Kim wrote: > On Wed, Jan 26, 2022 at 06:04:50PM +0100, David Hildenbrand wrote: >> On 26.01.22 18:00, Jonghyeon Kim wrote: >>> Export shrink_zone_span() and update_pgdat_span() functions to head >>> file. We need to update real number of spanned pages for NUMA nodes and >>> zones when we add memory device node such as device dax memory. >>> >> >> Can you elaborate a bit more what you intend to fix? >> >> Memory onlining/offlining is reponsible for updating the node/zone span, >> and that's triggered when the dax/kmem mamory gets onlined/offlined. >> > Sure, sorry for the lack of explanation of the intended fix. > > Before onlining nvdimm memory using dax(devdax or fsdax), these memory belong to > cpu NUMA nodes, which extends span pages of node/zone as a ZONE_DEVICE. So there > is no problem because node/zone contain these additional non-visible memory > devices to the system. > But, if we online dax-memory, zone[ZONE_DEVICE] of CPU NUMA node is hot-plugged > to new NUMA node(but CPU-less). I think there is no need to hold > zone[ZONE_DEVICE] pages on the original node. > > Additionally, spanned pages are also used to calculate the end pfn of a node. > Thus, it is needed to maintain accurate page stats for node/zone. > > My machine contains two CPU-socket consisting of DRAM and Intel DCPMM > (DC persistent memory modules) with App-Direct mode. > > Below are my test results. > > Before memory onlining: > > # ndctl create-namespace --mode=devdax > # ndctl create-namespace --mode=devdax > # cat /proc/zoneinfo | grep -E "Node|spanned" | paste - - > Node 0, zone DMA spanned 4095 > Node 0, zone DMA32 spanned 1044480 > Node 0, zone Normal spanned 7864320 > Node 0, zone Movable spanned 0 > Node 0, zone Device spanned 66060288 > Node 1, zone DMA spanned 0 > Node 1, zone DMA32 spanned 0 > Node 1, zone Normal spanned 8388608 > Node 1, zone Movable spanned 0 > Node 1, zone Device spanned 66060288 > > After memory onlining: > > # daxctl reconfigure-device --mode=system-ram --no-online dax0.0 > # daxctl reconfigure-device --mode=system-ram --no-online dax1.0 > > # cat /proc/zoneinfo | grep -E "Node|spanned" | paste - - > Node 0, zone DMA spanned 4095 > Node 0, zone DMA32 spanned 1044480 > Node 0, zone Normal spanned 7864320 > Node 0, zone Movable spanned 0 > Node 0, zone Device spanned 66060288 > Node 1, zone DMA spanned 0 > Node 1, zone DMA32 spanned 0 > Node 1, zone Normal spanned 8388608 > Node 1, zone Movable spanned 0 > Node 1, zone Device spanned 66060288 > Node 2, zone DMA spanned 0 > Node 2, zone DMA32 spanned 0 > Node 2, zone Normal spanned 65011712 > Node 2, zone Movable spanned 0 > Node 2, zone Device spanned 0 > Node 3, zone DMA spanned 0 > Node 3, zone DMA32 spanned 0 > Node 3, zone Normal spanned 65011712 > Node 3, zone Movable spanned 0 > Node 3, zone Device spanned 0 > > As we can see, Node 0 and 1 still have zone_device pages after memory onlining. > This causes problem that Node 0 and Node 2 have same end of pfn values, also > Node 1 and Node 3 have same problem. Thanks for the information, that makes it clearer. While this unfortunate, the node/zone span is something fairly unreliable/unusable for user space. Nodes and zones can overlap just easily. What counts are present/managed pages in the node/zone. So at least I don't count this as something that "needs fixing", it's more something that's nice to handle better if easily possible. See below. > >>> Signed-off-by: Jonghyeon Kim >>> --- >>> include/linux/memory_hotplug.h | 3 +++ >>> mm/memory_hotplug.c | 6 ++++-- >>> 2 files changed, 7 insertions(+), 2 deletions(-) >>> >>> diff --git a/include/linux/memory_hotplug.h b/include/linux/memory_hotplug.h >>> index be48e003a518..25c7f60c317e 100644 >>> --- a/include/linux/memory_hotplug.h >>> +++ b/include/linux/memory_hotplug.h >>> @@ -337,6 +337,9 @@ extern void move_pfn_range_to_zone(struct zone *zone, unsigned long start_pfn, >>> extern void remove_pfn_range_from_zone(struct zone *zone, >>> unsigned long start_pfn, >>> unsigned long nr_pages); >>> +extern void shrink_zone_span(struct zone *zone, unsigned long start_pfn, >>> + unsigned long end_pfn); >>> +extern void update_pgdat_span(struct pglist_data *pgdat); >>> extern bool is_memblock_offlined(struct memory_block *mem); >>> extern int sparse_add_section(int nid, unsigned long pfn, >>> unsigned long nr_pages, struct vmem_altmap *altmap); >>> diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c >>> index 2a9627dc784c..38f46a9ef853 100644 >>> --- a/mm/memory_hotplug.c >>> +++ b/mm/memory_hotplug.c >>> @@ -389,7 +389,7 @@ static unsigned long find_biggest_section_pfn(int nid, struct zone *zone, >>> return 0; >>> } >>> >>> -static void shrink_zone_span(struct zone *zone, unsigned long start_pfn, >>> +void shrink_zone_span(struct zone *zone, unsigned long start_pfn, >>> unsigned long end_pfn) >>> { >>> unsigned long pfn; >>> @@ -428,8 +428,9 @@ static void shrink_zone_span(struct zone *zone, unsigned long start_pfn, >>> } >>> } >>> } >>> +EXPORT_SYMBOL_GPL(shrink_zone_span); >> >> Exporting both as symbols feels very wrong. This is memory >> onlining/offlining internal stuff. > > I agree with you that your comment. I will find another approach to avoid > directly using onlining/offlining internal stuff while updating node/zone span. IIRC, to handle what you intend to handle properly want to look into teaching remove_pfn_range_from_zone() to handle zone_is_zone_device(). There is a big fat comment: /* * Zone shrinking code cannot properly deal with ZONE_DEVICE. So * we will not try to shrink the zones - which is okay as * set_zone_contiguous() cannot deal with ZONE_DEVICE either way. */ if (zone_is_zone_device(zone)) return; Similarly, try_offline_node() spells this out: /* * If the node still spans pages (especially ZONE_DEVICE), don't * offline it. A node spans memory after move_pfn_range_to_zone(), * e.g., after the memory block was onlined. */ if (pgdat->node_spanned_pages) return; So once you handle remove_pfn_range_from_zone() cleanly, you'll cleanly handle try_offline_node() implicitly. Trying to update the node span manually without teaching node/zone shrinking code how to handle ZONE_DEVICE properly is just a hack that will only sometimes work. Especially, it won't work if the range of interest is still surrounded by other ranges. -- Thanks, David / dhildenb