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Message-ID: <6489b23bc67e0_142af829456@dwillia2-xfh.jf.intel.com.notmuch>
Date: Wed, 14 Jun 2023 05:27:39 -0700
From: Dan Williams <dan.j.williams@...el.com>
To: "Wilczynski, Michal" <michal.wilczynski@...el.com>,
<alison.schofield@...el.com>,
"Rafael J. Wysocki" <rafael@...nel.org>,
"Len Brown" <lenb@...nel.org>,
Dan Williams <dan.j.williams@...el.com>,
"Thomas Gleixner" <tglx@...utronix.de>,
Ingo Molnar <mingo@...hat.com>,
"Borislav Petkov" <bp@...en8.de>,
Dave Hansen <dave.hansen@...ux.intel.com>,
"H. Peter Anvin" <hpa@...or.com>,
Andy Lutomirski <luto@...nel.org>,
Peter Zijlstra <peterz@...radead.org>,
Andrew Morton <akpm@...ux-foundation.org>,
"Jonathan Cameron" <Jonathan.Cameron@...wei.com>,
Dave Jiang <dave.jiang@...el.com>,
Mike Rapoport <rppt@...nel.org>
CC: <x86@...nel.org>, <linux-cxl@...r.kernel.org>,
<linux-acpi@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
Derick Marks <derick.w.marks@...el.com>
Subject: Re: [PATCH v2 1/2] x86/numa: Introduce numa_fill_memblks()
Wilczynski, Michal wrote:
>
>
> On 6/14/2023 6:35 AM, alison.schofield@...el.com wrote:
> > From: Alison Schofield <alison.schofield@...el.com>
> >
> > numa_fill_memblks() fills in the gaps in numa_meminfo memblks
> > over an HPA 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@...el.com>
> > Suggested-by: Dan Williams <dan.j.williams@...el.com>
> > Signed-off-by: Alison Schofield <alison.schofield@...el.com>
> > Tested-by: Derick Marks <derick.w.marks@...el.com>
> > ---
> > arch/x86/include/asm/sparsemem.h | 2 +
> > arch/x86/mm/numa.c | 87 ++++++++++++++++++++++++++++++++
> > include/linux/numa.h | 7 +++
> > 3 files changed, 96 insertions(+)
> >
> > diff --git a/arch/x86/include/asm/sparsemem.h b/arch/x86/include/asm/sparsemem.h
> > index 64df897c0ee3..1be13b2dfe8b 100644
> > --- a/arch/x86/include/asm/sparsemem.h
> > +++ b/arch/x86/include/asm/sparsemem.h
> > @@ -37,6 +37,8 @@ extern int phys_to_target_node(phys_addr_t start);
> > #define phys_to_target_node phys_to_target_node
> > extern int memory_add_physaddr_to_nid(u64 start);
> > #define memory_add_physaddr_to_nid memory_add_physaddr_to_nid
> > +extern int numa_fill_memblks(u64 start, u64 end);
> > +#define numa_fill_memblks numa_fill_memblks
> > #endif
> > #endif /* __ASSEMBLY__ */
> >
> > diff --git a/arch/x86/mm/numa.c b/arch/x86/mm/numa.c
> > index 2aadb2019b4f..fa82141d1a04 100644
> > --- a/arch/x86/mm/numa.c
> > +++ b/arch/x86/mm/numa.c
> > @@ -11,6 +11,7 @@
> > #include <linux/nodemask.h>
> > #include <linux/sched.h>
> > #include <linux/topology.h>
> > +#include <linux/sort.h>
> >
> > #include <asm/e820/api.h>
> > #include <asm/proto.h>
> > @@ -961,4 +962,90 @@ int memory_add_physaddr_to_nid(u64 start)
> > return nid;
> > }
> > EXPORT_SYMBOL_GPL(memory_add_physaddr_to_nid);
> > +
> > +static int __init cmp_memblk(const void *a, const void *b)
> > +{
> > + const struct numa_memblk *ma = *(const struct numa_memblk **)a;
> > + const struct numa_memblk *mb = *(const struct numa_memblk **)b;
>
> Is this casting necessary ?
This is idiomatic for sort() comparison handlers.
> > +
> > + if (ma->start != mb->start)
> > + return (ma->start < mb->start) ? -1 : 1;
> > +
> > + /* Caller handles duplicate start addresses */
> > + return 0;
> > +}
> > +
> > +static struct numa_memblk *numa_memblk_list[NR_NODE_MEMBLKS] __initdata;
> > +
> > +/**
> > + * numa_fill_memblks - Fill gaps in numa_meminfo memblks
> > + * @start: address to begin fill
> > + * @end: address to end fill
> > + *
> > + * Find and extend numa_meminfo memblks to cover the @start-@end
> > + * HPA address range, such that the first memblk includes @start,
> > + * the last memblk includes @end, and any gaps in between are
> > + * filled.
> > + *
> > + * RETURNS:
> > + * 0 : Success
> > + * NUMA_NO_MEMBLK : No memblk exists in @start-@end range
> > + */
> > +
> > +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,
> > + * prev_end, and backfilling to it if needed. Avoid filling
> > + * overlapping memblks by making prev_end monotonically non-
> > + * decreasing.
> > + */
> > + 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);
> > +
> > #endif
> > diff --git a/include/linux/numa.h b/include/linux/numa.h
> > index 59df211d051f..0f512c0aba54 100644
> > --- a/include/linux/numa.h
> > +++ b/include/linux/numa.h
> > @@ -12,6 +12,7 @@
> > #define MAX_NUMNODES (1 << NODES_SHIFT)
> >
> > #define NUMA_NO_NODE (-1)
> > +#define NUMA_NO_MEMBLK (-1)
>
> Same error code as NUMA_NO_NODE ?
>
> >
> > /* optionally keep NUMA memory info available post init */
> > #ifdef CONFIG_NUMA_KEEP_MEMINFO
> > @@ -43,6 +44,12 @@ static inline int phys_to_target_node(u64 start)
> > return 0;
> > }
> > #endif
> > +#ifndef numa_fill_memblks
>
> Why not just #ifndef CONFIG_NUMA_KEEP_MEMINFO ?
This is due to the fact that multiple archs use
CONFIG_NUMA_KEEP_MEMINFO (x86, ARM64, LOONGARCH), but only one supplies
a numa_fill_memblks() implementation (x86).
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