Message-ID: <de209828-d237-4912-905b-8c7de7e5734d@linux.ibm.com>
Date: Wed, 4 Jun 2025 18:57:33 +0530
From: Donet Tom <donettom@...ux.ibm.com>
To: David Hildenbrand <david@...hat.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Mike Rapoport <rppt@...nel.org>, Oscar Salvador <osalvador@...e.de>,
        Zi Yan <ziy@...dia.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc: Ritesh Harjani <ritesh.list@...il.com>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, "Rafael J . Wysocki" <rafael@...nel.org>,
        Danilo Krummrich <dakr@...nel.org>,
        Jonathan Cameron <Jonathan.Cameron@...wei.com>,
        Alison Schofield <alison.schofield@...el.com>,
        Yury Norov <yury.norov@...il.com>, Dave Jiang <dave.jiang@...el.com>,
        Madhavan Srinivasan <maddy@...ux.ibm.com>,
        Nilay Shroff
 <nilay@...ux.ibm.com>, linuxppc-dev@...ts.ozlabs.org
Subject: Re: [PATCH v7 1/5] drivers/base/node: Optimize memory block
 registration to reduce boot time


On 6/4/25 3:08 PM, David Hildenbrand wrote:
> On 28.05.25 19:18, Donet Tom wrote:
>> During node device initialization, `memory blocks` are registered under
>> each NUMA node. The `memory blocks` to be registered are identified 
>> using
>> the node’s start and end PFNs, which are obtained from the node's 
>> pg_data
>>
>> However, not all PFNs within this range necessarily belong to the same
>> node—some may belong to other nodes. Additionally, due to the
>> discontiguous nature of physical memory, certain sections within a
>> `memory block` may be absent.
>>
>> As a result, `memory blocks` that fall between a node’s start and end
>> PFNs may span across multiple nodes, and some sections within those 
>> blocks
>> may be missing. `Memory blocks` have a fixed size, which is architecture
>> dependent.
>>
>> Due to these considerations, the memory block registration is currently
>> performed as follows:
>>
>> for_each_online_node(nid):
>>      start_pfn = pgdat->node_start_pfn;
>>      end_pfn = pgdat->node_start_pfn + node_spanned_pages;
>>      for_each_memory_block_between(PFN_PHYS(start_pfn), 
>> PFN_PHYS(end_pfn))
>>          mem_blk = memory_block_id(pfn_to_section_nr(pfn));
>> pfn_mb_start=section_nr_to_pfn(mem_blk->start_section_nr)
>>          pfn_mb_end = pfn_start + memory_block_pfns - 1
>>          for (pfn = pfn_mb_start; pfn < pfn_mb_end; pfn++):
>>              if (get_nid_for_pfn(pfn) != nid):
>>                  continue;
>>              else
>>                  do_register_memory_block_under_node(nid, mem_blk,
>> MEMINIT_EARLY);
>>
>> Here, we derive the start and end PFNs from the node's pg_data, then
>> determine the memory blocks that may belong to the node. For each
>> `memory block` in this range, we inspect all PFNs it contains and check
>> their associated NUMA node ID. If a PFN within the block matches the
>> current node, the memory block is registered under that node.
>>
>> If CONFIG_DEFERRED_STRUCT_PAGE_INIT is enabled, get_nid_for_pfn() 
>> performs
>> a binary search in the `memblock regions` to determine the NUMA node ID
>> for a given PFN. If it is not enabled, the node ID is retrieved directly
>> from the struct page.
>>
>> On large systems, this process can become time-consuming, especially 
>> since
>> we iterate over each `memory block` and all PFNs within it until a 
>> match is
>> found. When CONFIG_DEFERRED_STRUCT_PAGE_INIT is enabled, the additional
>> overhead of the binary search increases the execution time 
>> significantly,
>> potentially leading to soft lockups during boot.
>>
>> In this patch, we iterate over `memblock region` to identify the
>> `memory blocks` that belong to the current NUMA node. `memblock regions`
>> are contiguous memory ranges, each associated with a single NUMA 
>> node, and
>> they do not span across multiple nodes.
>>
>> for_each_memory_region(r): // r => region
>>    if (!node_online(r->nid)):
>>      continue;
>>    else
>>      for_each_memory_block_between(r->base, r->base + r->size - 1):
>>        do_register_memory_block_under_node(r->nid, mem_blk, 
>> MEMINIT_EARLY);
>>
>> We iterate over all memblock regions, and if the node associated with 
>> the
>> region is online, we calculate the start and end memory blocks based 
>> on the
>> region's start and end PFNs. We then register all the memory blocks 
>> within
>> that range under the region node.
>>
>> Test Results on My system with 32TB RAM
>> =======================================
>> 1. Boot time with CONFIG_DEFERRED_STRUCT_PAGE_INIT enabled.
>>
>> Without this patch
>> ------------------
>> Startup finished in 1min 16.528s (kernel)
>>
>> With this patch
>> ---------------
>> Startup finished in 17.236s (kernel) - 78% Improvement
>>
>> 2. Boot time with CONFIG_DEFERRED_STRUCT_PAGE_INIT disabled.
>>
>> Without this patch
>> ------------------
>> Startup finished in 28.320s (kernel)
>>
>> With this patch
>> ---------------
>> Startup finished in 15.621s (kernel) - 46% Improvement
>>
>> Acked-by: David Hildenbrand <david@...hat.com>
>> Acked-by: Oscar Salvador <osalvador@...e.de>
>> Acked-by: Mike Rapoport (Microsoft) <rppt@...nel.org>
>> Acked-by: Zi Yan <ziy@...dia.com>
>> Signed-off-by: Donet Tom <donettom@...ux.ibm.com>
>>
>> ---
>
> [...]
>
>>   #ifdef CONFIG_NUMA
>>   void memory_block_add_nid(struct memory_block *mem, int nid,
>>                 enum meminit_context context);
>> @@ -188,5 +206,4 @@ void memory_block_add_nid(struct memory_block 
>> *mem, int nid,
>>    * can sleep.
>>    */
>>   extern struct mutex text_mutex;
>> -
>
> ^ Nit: unrelated change?


Thank you David

I’ll make the change and send the next revision.

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