linux-kernel - Re: [PATCH v4 1/4] memblock tests: add simulation of physical memory with multiple NUMA nodes

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Date:   Tue, 6 Sep 2022 18:43:06 -0500
From:   Rebecca Mckeever <remckee0@...il.com>
To:     David Hildenbrand <david@...hat.com>
Cc:     Mike Rapoport <rppt@...nel.org>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4 1/4] memblock tests: add simulation of physical memory
 with multiple NUMA nodes

On Tue, Sep 06, 2022 at 03:17:46PM +0200, David Hildenbrand wrote:
> On 04.09.22 06:21, Rebecca Mckeever wrote:
> > Add function setup_numa_memblock() for setting up a memory layout with
> > multiple NUMA nodes in a previously allocated dummy physical memory.
> > This function can be used in place of setup_memblock() in tests that need
> > to simulate a NUMA system.
> > 
> > setup_numa_memblock():
> > - allows for setting up a memory layout by specifying the fraction of
> >    MEM_SIZE in each node
> > 
> > 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         | 29 +++++++++++++++++++
> >   tools/testing/memblock/tests/common.h         |  4 ++-
> >   3 files changed, 33 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..b6110df21b2a 100644
> > --- a/tools/testing/memblock/tests/common.c
> > +++ b/tools/testing/memblock/tests/common.c
> > @@ -72,6 +72,35 @@ void setup_memblock(void)
> >   	fill_memblock();
> >   }
> > +/**
> > + * setup_numa_memblock:
> > + * Set up a memory layout with multiple NUMA nodes in a previously allocated
> > + * dummy physical memory.
> > + * @nodes: an array containing the denominators of the fractions of MEM_SIZE
> > + *         contained in each node (e.g., if nodes[0] = SZ_8, node 0 will
> > + *         contain 1/8th of MEM_SIZE)
> > + *
> > + * The nids will be set to 0 through NUMA_NODES - 1.
> > + */
> > +void setup_numa_memblock(const phys_addr_t nodes[])
> > +{
> > +	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 < NUMA_NODES; i++) {
> > +		assert(nodes[i] <= MEM_SIZE && nodes[i] > 0);
> 
> I think it would be even easier to get if this would just be a fraction.
> E.g., instead of "1/8 * MEM_SIZE" just "1/8". All values have to add up to
> 1.
> 
> ... but then we'd have to mess with floats eventually, so I guess this makes
> it easier to handle these fractions.
> 
> 
> We could use "int" and simply specify the fraction in percent, like
> 
> nodes[0] = 50;
> nodes[1] = 25;
> nodes[2] = 25;
> 
> and everything has to add up to 100.
> 
This would still be a float for 1/8th (12.5) and 1/16th (6.25). What if
it was the "percent" of 256 (i.e., 0x100)?
> 
> > +		phys_addr_t size = MEM_SIZE / nodes[i];
> 
> 
> Hmmm, assuming a single node with "MEM_SIZE", we would get size=1.
> 
For a single node of MEM_SIZE, nodes[0] would be 1.

> Shouldn't this be "size = nodes[i]"
> 
> ?
No, not with the current implementation. The nodes array stores the
denominator of the fraction that will be multiplied by MEM_SIZE to
determine the size of that node (the numerator is always 1). So if the
size of the node should be 1/8 * MEM_SIZE, the nodes array just stores
the 8. I think the name of the array is misleading. Do you have any
suggestions for a better name?
> 
> -- 
> Thanks,
> 
> David / dhildenb
> 
Thanks,
Rebecca