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Message-ID: <da9c6b2f-5b4b-444c-a453-cf72272c2fb7@redhat.com>
Date: Mon, 28 Apr 2025 23:19:32 +0200
From: David Hildenbrand <david@...hat.com>
To: Donet Tom <donettom@...ux.ibm.com>, Mike Rapoport <rppt@...nel.org>,
Oscar Salvador <osalvador@...e.de>,
Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
Andrew Morton <akpm@...ux-foundation.org>, rafael@...nel.org,
Danilo Krummrich <dakr@...nel.org>
Cc: Ritesh Harjani <ritesh.list@...il.com>,
Jonathan Cameron <Jonathan.Cameron@...wei.com>,
Alison Schofield <alison.schofield@...el.com>,
Yury Norov <yury.norov@...il.com>, Dave Jiang <dave.jiang@...el.com>,
linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 1/2] driver/base: Optimize memory block registration to
reduce boot time
On 28.04.25 19:03, 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_online_node(nid):
> for_each_memory_region(r): // r => region
> if (r->nid != nid):
> continue;
> else
> for_each_memory_block_between(r->base, r->base + r->size - 1):
> do_register_memory_block_under_node(nid, mem_blk, MEMINIT_EARLY);
>
> We iterate over all `memblock regions` and identify those that belong to
> the current NUMA node. For each `memblock region` associated with the
> current node, we calculate the start and end `memory blocks` based on the
> region's start and end PFNs. We then register all `memory blocks` within
> that range under the current node.
Yes, makes sense.
>
> 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
Wow!
>
> 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
>
Also very nice!
> Signed-off-by: Donet Tom <donettom@...ux.ibm.com>
> ---
>
> v1->v2
>
> Reworked the implementation according to suggestions from
> Mike Rapoport[1]
>
> [1] - https://lore.kernel.org/all/Z_j2Gv9n4DOj6LSs@kernel.org/
>
> v1 - https://lore.kernel.org/all/50142a29010463f436dc5c4feb540e5de3bb09df.1744175097.git.donettom@linux.ibm.com/
> ---
> drivers/base/memory.c | 4 ++--
> drivers/base/node.c | 39 +++++++++++++++++++++++++++++++++++++++
> include/linux/memory.h | 2 ++
> include/linux/node.h | 11 +++++------
> 4 files changed, 48 insertions(+), 8 deletions(-)
>
> diff --git a/drivers/base/memory.c b/drivers/base/memory.c
> index 19469e7f88c2..7f1d266ae593 100644
> --- a/drivers/base/memory.c
> +++ b/drivers/base/memory.c
> @@ -60,7 +60,7 @@ static inline unsigned long pfn_to_block_id(unsigned long pfn)
> return memory_block_id(pfn_to_section_nr(pfn));
> }
>
> -static inline unsigned long phys_to_block_id(unsigned long phys)
> +unsigned long phys_to_block_id(unsigned long phys)
> {
> return pfn_to_block_id(PFN_DOWN(phys));
> }
> @@ -632,7 +632,7 @@ int __weak arch_get_memory_phys_device(unsigned long start_pfn)
> *
> * Called under device_hotplug_lock.
> */
> -static struct memory_block *find_memory_block_by_id(unsigned long block_id)
> +struct memory_block *find_memory_block_by_id(unsigned long block_id)
> {
> struct memory_block *mem;
>
> diff --git a/drivers/base/node.c b/drivers/base/node.c
> index cd13ef287011..4869333d366d 100644
> --- a/drivers/base/node.c
> +++ b/drivers/base/node.c
> @@ -20,6 +20,7 @@
> #include <linux/pm_runtime.h>
> #include <linux/swap.h>
> #include <linux/slab.h>
> +#include <linux/memblock.h>
>
> static const struct bus_type node_subsys = {
> .name = "node",
> @@ -850,6 +851,44 @@ void unregister_memory_block_under_nodes(struct memory_block *mem_blk)
> kobject_name(&node_devices[mem_blk->nid]->dev.kobj));
> }
>
> +/*
> + * register_memory_blocks_under_node_early : Register the memory
> + * blocks under the current node.
> + * @nid : Current node under registration
> + *
> + * This function iterates over all memblock regions and identifies the regions
> + * that belong to the current node. For each region which belongs to current
> + * node, it calculates the start and end memory blocks based on the region's
> + * start and end PFNs. It then registers all memory blocks within that range
> + * under the current node.
> + *
> + */
> +void register_memory_blocks_under_node_early(int nid)
> +{
> + struct memblock_region *r;
You almost achieved a reverse x-mas tree :)
> + unsigned long start_block_id;
> + unsigned long end_block_id;
> + struct memory_block *mem;
> + unsigned long block_id;
> +
> + for_each_mem_region(r) {
> + if (r->nid == nid) {
To reduce indentation
if (r->nid != nid)
continue;
> + start_block_id = phys_to_block_id(r->base);
> + end_block_id = phys_to_block_id(r->base + r->size - 1);
Probably you could make them const in the for loop
const unsigned long start_block_id = phys_to_block_id(r->base);
const unsigned long end_block_id = phys_to_block_id(r->base + r->size - 1);
Okay, so end is inclusive as well.
> +
> + for (block_id = start_block_id; block_id <= end_block_id; block_id++) {
> + mem = find_memory_block_by_id(block_id);
> + if (!mem)
> + continue;
> +
> + do_register_memory_block_under_node(nid, mem, MEMINIT_EARLY);
--
Cheers,
David / dhildenb
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