Re: [PATCH v3 3/3] acpi,srat: give memory block size advice based on CFMWS alignment

[Gregory Price <gourry@gourry.net>]

On Mon, Oct 28, 2024 at 07:24:54PM +0200, Mike Rapoport wrote:
> On Tue, Oct 22, 2024 at 05:34:50PM -0400, Gregory Price wrote:
> > Capacity is stranded when CFMWS regions are not aligned to block size.
> > On x86, block size increases with capacity (2G blocks @ 64G capacity).
> > 
> > Use CFMWS base/size to report memory block size alignment advice.
> > 
> > After the alignment, the acpi code begins populating numa nodes with
> > memblocks, so probe the value just prior to lock it in.  All future
> > callers should be providing advice prior to this point.
> > 
> > Suggested-by: Dan Williams <dan.j.williams@intel.com>
> > Signed-off-by: Gregory Price <gourry@gourry.net>
> > ---
> >  drivers/acpi/numa/srat.c | 33 +++++++++++++++++++++++++++++++++
> >  1 file changed, 33 insertions(+)
> > 
... snip ...
> > +	/* Align memblock size to CFMW regions if possible */
> > +	acpi_table_parse_cedt(ACPI_CEDT_TYPE_CFMWS, acpi_align_cfmws, NULL);
> > +
> > +	/*
> > +	 * Nodes start populating with blocks after this, so probe the max
> > +	 * block size to prevent it from changing in the future.
> > +	 */
> > +	memory_block_probe_max_size();
> > +
> 
> It won't change, but how drivers/base/memory.c will know about the probed
> size if architecture does not override memory_block_size_bytes()?
> 

non-arch code should be calling memory_block_size_bytes() to discover
the actual size of blocks - and for archs that care about this value,
that is when it should be probed.  It's up to the arch whether/how to use
this information.  Many archs ignore it entirely and use MIN_BLOCK_SIZE.

basically non-arch code shouldn't care what this value is, and even most
arch code shouldn't care.


I added this call to probe to lock in the size since I saw that nodes
will start populating blocks immediately after this.

Possibly the APIs should be marked __init so that the whole interface
disappears after init to avoid misuse post-init.

Possibly probe() should return -EBUSY if called more than once to
enforce a particular probe pattern on the architectures?

Open to thoughts here.

> >  	/* fake_pxm is the next unused PXM value after SRAT parsing */
> >  	for (i = 0, fake_pxm = -1; i < MAX_NUMNODES; i++) {
> >  		if (node_to_pxm_map[i] > fake_pxm)
> > -- 
> > 2.43.0
> > 
> 
> -- 
> Sincerely yours,
> Mike.