linux-kernel - Re: [PATCH v2 1/4] memblock tests: add simulation of physical memory with multiple NUMA nodes

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Message-ID: <7c83950c-6a83-e35b-0060-79b5df3bda56@redhat.com>
Date:   Thu, 1 Sep 2022 10:06:48 +0200
From:   David Hildenbrand <david@...hat.com>
To:     Rebecca Mckeever <remckee0@...il.com>
Cc:     Mike Rapoport <rppt@...nel.org>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 1/4] memblock tests: add simulation of physical memory
 with multiple NUMA nodes

On 31.08.22 05:49, Rebecca Mckeever wrote:
> On Tue, Aug 30, 2022 at 01:17:56PM +0200, David Hildenbrand wrote:
>> On 19.08.22 11:05, Rebecca Mckeever wrote:
>>> Add functions setup_numa_memblock_generic() and setup_numa_memblock()
>>> for setting up a memory layout with multiple NUMA nodes in a previously
>>> allocated dummy physical memory. These functions can be used in place of
>>> setup_memblock() in tests that need to simulate a NUMA system.
>>>
>>> setup_numa_memblock_generic():
>>> - allows for setting up a custom memory layout by specifying the amount
>>>   of memory in each node, the number of nodes, and a factor that will be
>>>   used to scale the memory in each node
>>>
>>> setup_numa_memblock():
>>> - allows for setting up a default memory layout
>>>
>>> Introduce constant MEM_FACTOR, which is used to scale the default memory
>>> layout based on MEM_SIZE.
>>>
>>> Set CONFIG_NODES_SHIFT to 4 when building with NUMA=1 to allow for up to
>>> 16 NUMA nodes.
>>>
>>> Signed-off-by: Rebecca Mckeever <remckee0@...il.com>
>>> ---
>>>  .../testing/memblock/scripts/Makefile.include |  2 +-
>>>  tools/testing/memblock/tests/common.c         | 38 +++++++++++++++++++
>>>  tools/testing/memblock/tests/common.h         |  9 ++++-
>>>  3 files changed, 47 insertions(+), 2 deletions(-)
>>>
>>> diff --git a/tools/testing/memblock/scripts/Makefile.include b/tools/testing/memblock/scripts/Makefile.include
>>> index aa6d82d56a23..998281723590 100644
>>> --- a/tools/testing/memblock/scripts/Makefile.include
>>> +++ b/tools/testing/memblock/scripts/Makefile.include
>>> @@ -3,7 +3,7 @@
>>>  
>>>  # Simulate CONFIG_NUMA=y
>>>  ifeq ($(NUMA), 1)
>>> -	CFLAGS += -D CONFIG_NUMA
>>> +	CFLAGS += -D CONFIG_NUMA -D CONFIG_NODES_SHIFT=4
>>>  endif
>>>  
>>>  # Use 32 bit physical addresses.
>>> diff --git a/tools/testing/memblock/tests/common.c b/tools/testing/memblock/tests/common.c
>>> index eec6901081af..15d8767dc70c 100644
>>> --- a/tools/testing/memblock/tests/common.c
>>> +++ b/tools/testing/memblock/tests/common.c
>>> @@ -34,6 +34,10 @@ static const char * const help_opts[] = {
>>>  
>>>  static int verbose;
>>>  
>>> +static const phys_addr_t node_sizes[] = {
>>> +	SZ_4K, SZ_1K, SZ_2K, SZ_2K, SZ_1K, SZ_1K, SZ_4K, SZ_1K
>>> +};
>>> +
>>>  /* sets global variable returned by movable_node_is_enabled() stub */
>>>  bool movable_node_enabled;
>>>  
>>> @@ -72,6 +76,40 @@ void setup_memblock(void)
>>>  	fill_memblock();
>>>  }
>>>  
>>> +/**
>>> + * setup_numa_memblock_generic:
>>> + * Set up a memory layout with multiple NUMA nodes in a previously allocated
>>> + * dummy physical memory.
>>> + * @nodes: an array containing the amount of memory in each node
>>> + * @node_cnt: the size of @nodes
>>> + * @factor: a factor that will be used to scale the memory in each node
>>> + *
>>> + * The nids will be set to 0 through node_cnt - 1.
>>> + */
>>> +void setup_numa_memblock_generic(const phys_addr_t nodes[],
>>> +				 int node_cnt, int factor)
>>> +{
>>> +	phys_addr_t base;
>>> +	int flags;
>>> +
>>> +	reset_memblock_regions();
>>> +	base = (phys_addr_t)memory_block.base;
>>> +	flags = (movable_node_is_enabled()) ? MEMBLOCK_NONE : MEMBLOCK_HOTPLUG;
>>> +
>>> +	for (int i = 0; i < node_cnt; i++) {
>>> +		phys_addr_t size = factor * nodes[i];
>>
>> I'm a bit lost why we need the factor if we already provide sizes in the
>> array.
>>
>> Can you enlighten me? :)
>>
>> Why can't we just stick to the sizes in the array?
>>
> Without the factor, some of the tests will break if we increase MEM_SIZE
> in the future (which we may need to do). I could rewrite them so that the
> factor is not needed, but I thought the code would be over-complicated if
> I did.

Independent of the suggestion from Mike, I wonder if we should really
care about (eventual) MEM_SIZE changes for now if not caring simplifies
the current code.

-- 
Thanks,

David / dhildenb