[v3,1/2] x86/numa: Introduce numa_fill_memblks()

From: Alison Schofield <alison.schofield@intel.com>

numa_fill_memblks() fills in the gaps in numa_meminfo memblks
over an physical address range.

The ACPI driver will use numa_fill_memblks() to implement a new Linux
policy that prescribes extending proximity domains in a portion of a
CFMWS window to the entire window.

Dan Williams offered this explanation of the policy:
A CFWMS is an ACPI data structure that indicates *potential* locations
where CXL memory can be placed. It is the playground where the CXL
driver has free reign to establish regions. That space can be populated
by BIOS created regions, or driver created regions, after hotplug or
other reconfiguration.

When BIOS creates a region in a CXL Window it additionally describes
that subset of the Window range in the other typical ACPI tables SRAT,
SLIT, and HMAT. The rationale for BIOS not pre-describing the entire
CXL Window in SRAT, SLIT, and HMAT is that it can not predict the
future. I.e. there is nothing stopping higher or lower performance
devices being placed in the same Window. Compare that to ACPI memory
hotplug that just onlines additional capacity in the proximity domain
with little freedom for dynamic performance differentiation.

That leaves the OS with a choice, should unpopulated window capacity
match the proximity domain of an existing region, or should it allocate
a new one? This patch takes the simple position of minimizing proximity
domain proliferation by reusing any proximity domain intersection for
the entire Window. If the Window has no intersections then allocate a
new proximity domain. Note that SRAT, SLIT and HMAT information can be
enumerated dynamically in a standard way from device provided data.
Think of CXL as the end of ACPI needing to describe memory attributes,
CXL offers a standard discovery model for performance attributes, but
Linux still needs to interoperate with the old regime.

Reported-by: Derick Marks <derick.w.marks@intel.com>
Suggested-by: Dan Williams <dan.j.williams@intel.com>
Signed-off-by: Alison Schofield <alison.schofield@intel.com>
Tested-by: Derick Marks <derick.w.marks@intel.com>
---
 arch/x86/include/asm/sparsemem.h |  2 +
 arch/x86/mm/numa.c               | 81 ++++++++++++++++++++++++++++++++
 include/linux/numa.h             |  7 +++
 3 files changed, 90 insertions(+)

alison.schofield@ wrote:
> From: Alison Schofield <alison.schofield@intel.com>
> 
> numa_fill_memblks() fills in the gaps in numa_meminfo memblks
> over an physical address range.
[..]
> diff --git a/arch/x86/mm/numa.c b/arch/x86/mm/numa.c
> index 2aadb2019b4f..152398bdecc4 100644
> --- a/arch/x86/mm/numa.c
> +++ b/arch/x86/mm/numa.c
[..]
> +int __init numa_fill_memblks(u64 start, u64 end)
> +{
> +	struct numa_memblk **blk = &numa_memblk_list[0];
> +	struct numa_meminfo *mi = &numa_meminfo;
> +	int count = 0;
> +	u64 prev_end;
> +
> +	/*
> +	 * Create a list of pointers to numa_meminfo memblks that
> +	 * overlap start, end. Exclude (start == bi->end) since
> +	 * end addresses in both a CFMWS range and a memblk range
> +	 * are exclusive.
> +	 *
> +	 * This list of pointers is used to make in-place changes
> +	 * that fill out the numa_meminfo memblks.
> +	 */
> +	for (int i = 0; i < mi->nr_blks; i++) {
> +		struct numa_memblk *bi = &mi->blk[i];
> +
> +		if (start < bi->end && end >= bi->start) {
> +			blk[count] = &mi->blk[i];
> +			count++;
> +		}
> +	}
> +	if (!count)
> +		return NUMA_NO_MEMBLK;
> +
> +	/* Sort the list of pointers in memblk->start order */
> +	sort(&blk[0], count, sizeof(blk[0]), cmp_memblk, NULL);
> +
> +	/* Make sure the first/last memblks include start/end */
> +	blk[0]->start = min(blk[0]->start, start);
> +	blk[count - 1]->end = max(blk[count - 1]->end, end);
> +
> +	/*
> +	 * Fill any gaps by tracking the previous memblks
> +	 * end address and backfilling to it if needed.
> +	 */
> +	prev_end = blk[0]->end;
> +	for (int i = 1; i < count; i++) {
> +		struct numa_memblk *curr = blk[i];
> +
> +		if (prev_end >= curr->start) {
> +			if (prev_end < curr->end)
> +				prev_end = curr->end;
> +		} else {
> +			curr->start = prev_end;
> +			prev_end = curr->end;
> +		}
> +	}
> +	return 0;
> +}
> +EXPORT_SYMBOL_GPL(numa_fill_memblks);

After deleting this export you can add:

Reviewed-by: Dan Williams <dan.j.williams@intel.com>

On Sat, Jun 24, 2023 at 11:01:38PM -0700, Dan Williams wrote:
> alison.schofield@ wrote:
> > From: Alison Schofield <alison.schofield@intel.com>
> > 
> > numa_fill_memblks() fills in the gaps in numa_meminfo memblks
> > over an physical address range.
> [..]
> > diff --git a/arch/x86/mm/numa.c b/arch/x86/mm/numa.c
> > index 2aadb2019b4f..152398bdecc4 100644
> > --- a/arch/x86/mm/numa.c
> > +++ b/arch/x86/mm/numa.c
> [..]
> > +int __init numa_fill_memblks(u64 start, u64 end)
> > +{
> > +	struct numa_memblk **blk = &numa_memblk_list[0];
> > +	struct numa_meminfo *mi = &numa_meminfo;
> > +	int count = 0;
> > +	u64 prev_end;
> > +
> > +	/*
> > +	 * Create a list of pointers to numa_meminfo memblks that
> > +	 * overlap start, end. Exclude (start == bi->end) since
> > +	 * end addresses in both a CFMWS range and a memblk range
> > +	 * are exclusive.
> > +	 *
> > +	 * This list of pointers is used to make in-place changes
> > +	 * that fill out the numa_meminfo memblks.
> > +	 */
> > +	for (int i = 0; i < mi->nr_blks; i++) {
> > +		struct numa_memblk *bi = &mi->blk[i];
> > +
> > +		if (start < bi->end && end >= bi->start) {
> > +			blk[count] = &mi->blk[i];
> > +			count++;
> > +		}
> > +	}
> > +	if (!count)
> > +		return NUMA_NO_MEMBLK;
> > +
> > +	/* Sort the list of pointers in memblk->start order */
> > +	sort(&blk[0], count, sizeof(blk[0]), cmp_memblk, NULL);
> > +
> > +	/* Make sure the first/last memblks include start/end */
> > +	blk[0]->start = min(blk[0]->start, start);
> > +	blk[count - 1]->end = max(blk[count - 1]->end, end);
> > +
> > +	/*
> > +	 * Fill any gaps by tracking the previous memblks
> > +	 * end address and backfilling to it if needed.
> > +	 */
> > +	prev_end = blk[0]->end;
> > +	for (int i = 1; i < count; i++) {
> > +		struct numa_memblk *curr = blk[i];
> > +
> > +		if (prev_end >= curr->start) {
> > +			if (prev_end < curr->end)
> > +				prev_end = curr->end;
> > +		} else {
> > +			curr->start = prev_end;
> > +			prev_end = curr->end;
> > +		}
> > +	}
> > +	return 0;
> > +}
> > +EXPORT_SYMBOL_GPL(numa_fill_memblks);
> 
> After deleting this export you can add:

Drats! Sorry for missing that.
> 
> Reviewed-by: Dan Williams <dan.j.williams@intel.com>