[PATCH v2 0/9] mm: introduce Designated Movable Blocks

[PATCH v2 0/9] mm: introduce Designated Movable Blocks

[Doug Berger]

MOTIVATION:
Some Broadcom devices (e.g. 7445, 7278) contain multiple memory
controllers with each mapped in a different address range within
a Uniform Memory Architecture. Some users of these systems have
expressed the desire to locate ZONE_MOVABLE memory on each
memory controller to allow user space intensive processing to
make better use of the additional memory bandwidth.
Unfortunately, the historical monotonic layout of zones would
mean that if the lowest addressed memory controller contains
ZONE_MOVABLE memory then all of the memory available from
memory controllers at higher addresses must also be in the
ZONE_MOVABLE zone. This would force all kernel memory accesses
onto the lowest addressed memory controller and significantly
reduce the amount of memory available for non-movable
allocations.

The main objective of this patch set is therefore to allow a
block of memory to be designated as part of the ZONE_MOVABLE
zone where it will always only be used by the kernel page
allocator to satisfy requests for movable pages. The term
Designated Movable Block is introduced here to represent such a
block. The favored implementation allows modification of the
'movablecore' kernel parameter to allow specification of a base
address and support for multiple blocks. The existing
'movablecore' mechanisms are retained.

BACKGROUND:
NUMA architectures support distributing movablecore memory
across each node, but it is undesirable to introduce the
overhead and complexities of NUMA on systems that don't have a
Non-Uniform Memory Architecture.

Commit 342332e6a925 ("mm/page_alloc.c: introduce kernelcore=mirror option")
also depends on zone overlap to support sytems with multiple
mirrored ranges.

Commit c6f03e2903c9 ("mm, memory_hotplug: remove zone restrictions")
embraced overlapped zones for memory hotplug.

This commit set follows their lead to allow the ZONE_MOVABLE
zone to overlap other zones while spanning the pages from the
lowest Designated Movable Block to the end of the node.
Designated Movable Blocks are made absent from overlapping zones
and present within the ZONE_MOVABLE zone.

I initially investigated an implementation using a Designated
Movable migrate type in line with comments[1] made by Mel Gorman
regarding a "sticky" MIGRATE_MOVABLE type to avoid using
ZONE_MOVABLE. However, this approach was riskier since it was
much more instrusive on the allocation paths. Ultimately, the
progress made by the memory hotplug folks to expand the
ZONE_MOVABLE functionality convinced me to follow this approach.

OTHER OPPORTUNITIES:
CMA introduced a paradigm where multiple allocators could
operate on the same region of memory, and that paradigm can be
extended to Designated Movable Blocks as well. I was interested
in using kernel resource management as a mechanism for exposing
Designated Movable Block resources (e.g. /proc/iomem) that would
be used by the kernel page allocator like any other ZONE_MOVABLE
memory, but could be claimed by an alternative allocator (e.g.
CMA). Unfortunately, this becomes complicated because the kernel
resource implementation varies materially across different
architectures and I do not require this capability so I have
deferred that.

The Devicetree Specification includes support for specifying
reserved memory regions with a 'reusable' property to allow
sharing of the reserved memory between device drivers and the
OS. This is in line with the paradigm introduced by CMA, but is
currently only used by 'shared-dma-pool' compatible reserved
memory regions. Linux could choose to use Designated Movable
Blocks as the default mechanism for other 'reusable' reserved
memory. Device drivers that own 'reusable' reserved memory could
use the dmb_intersects() function introduced here to determine
whether memory requires reclamation from the OS before use and
could use the alloc/free_contig_range() functions to perform the
reclamation and release of memory needed by the device. The CMA
allocator API could be another candidate for device driver
reclamation, but it is not currently exposed for use by device
drivers in modules.

There have been attempts to modify the behavior of the kernel
page allocators use of CMA regions (e.g. [1] & [2]). This
implementation of Designated Movable Blocks creates an
opportunity to allow the CMA allocator to operate on
ZONE_MOVABLE memory that the kernel page allocator can use more
agressively, without affecting users of the existing CMA
implementation. This would have benefit when memory reuse is
more valuable than the cost of increased latency of CMA
allocations (e.g. hugetlb_cma).

These other opportunities are dependent on the Designated
Movable Block concept introduced here, so I will hold off
submitting any such follow-on proposals until there is movement
on this commit set.

NOTES:
The MEMBLOCK_MOVABLE and MEMBLOCK_HOTPLUG flags have a lot in
common and could potentially be consolidated, but I chose to
avoid that here to reduce controversy.

The CMA and DMB alignment constraints are currently the same so
the logic could be simplified, but this implementation keeps
them distinct to facilitate independent evolution of the
implementations if necessary.

Changes in v2:
  - first three commits upstreamed separately [3], [4], and [5].
  - commits 04-06 submitted separately [6].
  - Corrected errors "Reported-by: kernel test robot <lkp@intel.com>"
  - Deferred commits after 15 to simplify review of the base
    functionality.
  - minor reorganization of commit 13.

v1: https://lore.kernel.org/linux-mm/20220913195508.3511038-1-opendmb@gmail.com/

[1] https://lore.kernel.org/lkml/20160428103927.GM2858@techsingularity.net/
[2] https://lore.kernel.org/lkml/1401260672-28339-1-git-send-email-iamjoonsoo.kim@lge.com
[3] https://lore.kernel.org/linux-mm/20220914023913.1855924-1-zi.yan@sent.com
[4] https://lore.kernel.org/linux-mm/20220823030209.57434-2-linmiaohe@huawei.com
[5] https://lore.kernel.org/linux-mm/20220914190917.3517663-1-opendmb@gmail.com
[6] https://lore.kernel.org/linux-mm/20220921223639.1152392-1-opendmb@gmail.com/

Doug Berger (9):
  lib/show_mem.c: display MovableOnly
  mm/vmstat: show start_pfn when zone spans pages
  mm/page_alloc: calculate node_spanned_pages from pfns
  mm/page_alloc.c: allow oversized movablecore
  mm/page_alloc: introduce init_reserved_pageblock()
  memblock: introduce MEMBLOCK_MOVABLE flag
  mm/dmb: Introduce Designated Movable Blocks
  mm/page_alloc: make alloc_contig_pages DMB aware
  mm/page_alloc: allow base for movablecore

 .../admin-guide/kernel-parameters.txt         |  14 +-
 include/linux/dmb.h                           |  29 ++++
 include/linux/gfp.h                           |   5 +-
 include/linux/memblock.h                      |   8 +
 lib/show_mem.c                                |   2 +-
 mm/Kconfig                                    |  12 ++
 mm/Makefile                                   |   1 +
 mm/cma.c                                      |  15 +-
 mm/dmb.c                                      |  91 ++++++++++
 mm/memblock.c                                 |  30 +++-
 mm/page_alloc.c                               | 155 ++++++++++++++----
 mm/vmstat.c                                   |   5 +
 12 files changed, 321 insertions(+), 46 deletions(-)
 create mode 100644 include/linux/dmb.h
 create mode 100644 mm/dmb.c

-- 
2.25.1

[PATCH v2 1/9] lib/show_mem.c: display MovableOnly

[Doug Berger]

The comment for commit c78e93630d15 ("mm: do not walk all of
system memory during show_mem") indicates it "also corrects the
reporting of HighMem as HighMem/MovableOnly as ZONE_MOVABLE has
similar problems to HighMem with respect to lowmem/highmem
exhaustion."

Presuming the similar problems are with regard to the general
exclusion of kernel allocations from either zone, I believe it
makes sense to include all ZONE_MOVABLE memory even on systems
without HighMem.

To the extent that this was the intent of the original commit I
have included a "Fixes" tag, but it seems unnecessary to submit
to linux-stable.

Fixes: c78e93630d15 ("mm: do not walk all of system memory during show_mem")
Signed-off-by: Doug Berger <opendmb@gmail.com>
---
 lib/show_mem.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/lib/show_mem.c b/lib/show_mem.c
index 1c26c14ffbb9..337c870a5e59 100644
--- a/lib/show_mem.c
+++ b/lib/show_mem.c
@@ -27,7 +27,7 @@ void show_mem(unsigned int filter, nodemask_t *nodemask)
 			total += zone->present_pages;
 			reserved += zone->present_pages - zone_managed_pages(zone);
 
-			if (is_highmem_idx(zoneid))
+			if (zoneid == ZONE_MOVABLE || is_highmem_idx(zoneid))
 				highmem += zone->present_pages;
 		}
 	}
-- 
2.25.1

[PATCH v2 2/9] mm/vmstat: show start_pfn when zone spans pages

[Doug Berger]

A zone that overlaps with another zone may span a range of pages
that are not present. In this case, displaying the start_pfn of
the zone allows the zone page range to be identified.

Signed-off-by: Doug Berger <opendmb@gmail.com>
---
 mm/vmstat.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/mm/vmstat.c b/mm/vmstat.c
index 90af9a8572f5..e2f19f2b7615 100644
--- a/mm/vmstat.c
+++ b/mm/vmstat.c
@@ -1717,6 +1717,11 @@ static void zoneinfo_show_print(struct seq_file *m, pg_data_t *pgdat,
 
 	/* If unpopulated, no other information is useful */
 	if (!populated_zone(zone)) {
+		/* Show start_pfn for empty overlapped zones */
+		if (zone->spanned_pages)
+			seq_printf(m,
+				   "\n  start_pfn:           %lu",
+				   zone->zone_start_pfn);
 		seq_putc(m, '\n');
 		return;
 	}
-- 
2.25.1

[PATCH v2 3/9] mm/page_alloc: calculate node_spanned_pages from pfns

[Doug Berger]

Since the start and end pfns of the node are passed as arguments
to calculate_node_totalpages() they might as well be used to
specify the node_spanned_pages value for the node rather than
accumulating the spans of member zones.

This prevents the need for additional adjustments if zones are
allowed to overlap.

Signed-off-by: Doug Berger <opendmb@gmail.com>
---
 mm/page_alloc.c | 5 ++---
 1 file changed, 2 insertions(+), 3 deletions(-)

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index e5486d47406e..3412d644c230 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -7452,7 +7452,7 @@ static void __init calculate_node_totalpages(struct pglist_data *pgdat,
 						unsigned long node_start_pfn,
 						unsigned long node_end_pfn)
 {
-	unsigned long realtotalpages = 0, totalpages = 0;
+	unsigned long realtotalpages = 0;
 	enum zone_type i;
 
 	for (i = 0; i < MAX_NR_ZONES; i++) {
@@ -7483,11 +7483,10 @@ static void __init calculate_node_totalpages(struct pglist_data *pgdat,
 		zone->present_early_pages = real_size;
 #endif
 
-		totalpages += size;
 		realtotalpages += real_size;
 	}
 
-	pgdat->node_spanned_pages = totalpages;
+	pgdat->node_spanned_pages = node_end_pfn - node_start_pfn;
 	pgdat->node_present_pages = realtotalpages;
 	pr_debug("On node %d totalpages: %lu\n", pgdat->node_id, realtotalpages);
 }
-- 
2.25.1

[PATCH v2 4/9] mm/page_alloc.c: allow oversized movablecore

[Doug Berger]

Now that the error in computation of corepages has been corrected
by commit 9fd745d450e7 ("mm: fix overflow in
find_zone_movable_pfns_for_nodes()"), oversized specifications of
movablecore will result in a zero value for required_kernelcore if
it is not also specified.

It is unintuitive for such a request to lead to no ZONE_MOVABLE
memory when the kernel parameters are clearly requesting some.

The current behavior when requesting an oversized kernelcore is to
classify all of the pages in movable_zone as kernelcore. The new
behavior when requesting an oversized movablecore (when not also
specifying kernelcore) is to similarly classify all of the pages
in movable_zone as movablecore.

Signed-off-by: Doug Berger <opendmb@gmail.com>
---
 mm/page_alloc.c | 10 +++++-----
 1 file changed, 5 insertions(+), 5 deletions(-)

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 3412d644c230..81f97c5ed080 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -8041,13 +8041,13 @@ static void __init find_zone_movable_pfns_for_nodes(void)
 		corepages = totalpages - required_movablecore;
 
 		required_kernelcore = max(required_kernelcore, corepages);
+	} else if (!required_kernelcore) {
+		/* If kernelcore was not specified, there is no ZONE_MOVABLE */
+		goto out;
 	}
 
-	/*
-	 * If kernelcore was not specified or kernelcore size is larger
-	 * than totalpages, there is no ZONE_MOVABLE.
-	 */
-	if (!required_kernelcore || required_kernelcore >= totalpages)
+	/* If kernelcore size exceeds totalpages, there is no ZONE_MOVABLE */
+	if (required_kernelcore >= totalpages)
 		goto out;
 
 	/* usable_startpfn is the lowest possible pfn ZONE_MOVABLE can be at */
-- 
2.25.1

[PATCH v2 5/9] mm/page_alloc: introduce init_reserved_pageblock()

[Doug Berger]

Most of the implementation of init_cma_reserved_pageblock() is
common to the initialization of any reserved pageblock for use
by the page allocator.

This commit breaks that functionality out into the new common
function init_reserved_pageblock() for use by code other than
CMA. The CMA specific code is relocated from page_alloc to the
point where init_cma_reserved_pageblock() was invoked and the
new function is used there instead. The error path is also
updated to use the function to operate on pageblocks rather
than pages.

Signed-off-by: Doug Berger <opendmb@gmail.com>
---
 include/linux/gfp.h |  5 +----
 mm/cma.c            | 15 +++++++++++----
 mm/page_alloc.c     |  8 ++------
 3 files changed, 14 insertions(+), 14 deletions(-)

diff --git a/include/linux/gfp.h b/include/linux/gfp.h
index f314be58fa77..71ed687be406 100644
--- a/include/linux/gfp.h
+++ b/include/linux/gfp.h
@@ -367,9 +367,6 @@ extern struct page *alloc_contig_pages(unsigned long nr_pages, gfp_t gfp_mask,
 #endif
 void free_contig_range(unsigned long pfn, unsigned long nr_pages);
 
-#ifdef CONFIG_CMA
-/* CMA stuff */
-extern void init_cma_reserved_pageblock(struct page *page);
-#endif
+extern void init_reserved_pageblock(struct page *page);
 
 #endif /* __LINUX_GFP_H */
diff --git a/mm/cma.c b/mm/cma.c
index 4a978e09547a..6208a3e1cd9d 100644
--- a/mm/cma.c
+++ b/mm/cma.c
@@ -31,6 +31,7 @@
 #include <linux/highmem.h>
 #include <linux/io.h>
 #include <linux/kmemleak.h>
+#include <linux/page-isolation.h>
 #include <trace/events/cma.h>
 
 #include "cma.h"
@@ -116,8 +117,13 @@ static void __init cma_activate_area(struct cma *cma)
 	}
 
 	for (pfn = base_pfn; pfn < base_pfn + cma->count;
-	     pfn += pageblock_nr_pages)
-		init_cma_reserved_pageblock(pfn_to_page(pfn));
+	     pfn += pageblock_nr_pages) {
+		struct page *page = pfn_to_page(pfn);
+
+		set_pageblock_migratetype(page, MIGRATE_CMA);
+		init_reserved_pageblock(page);
+		page_zone(page)->cma_pages += pageblock_nr_pages;
+	}
 
 	spin_lock_init(&cma->lock);
 
@@ -133,8 +139,9 @@ static void __init cma_activate_area(struct cma *cma)
 out_error:
 	/* Expose all pages to the buddy, they are useless for CMA. */
 	if (!cma->reserve_pages_on_error) {
-		for (pfn = base_pfn; pfn < base_pfn + cma->count; pfn++)
-			free_reserved_page(pfn_to_page(pfn));
+		for (pfn = base_pfn; pfn < base_pfn + cma->count;
+		     pfn += pageblock_nr_pages)
+			init_reserved_pageblock(pfn_to_page(pfn));
 	}
 	totalcma_pages -= cma->count;
 	cma->count = 0;
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 81f97c5ed080..6d4470b0daba 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -2302,9 +2302,8 @@ void __init page_alloc_init_late(void)
 		set_zone_contiguous(zone);
 }
 
-#ifdef CONFIG_CMA
-/* Free whole pageblock and set its migration type to MIGRATE_CMA. */
-void __init init_cma_reserved_pageblock(struct page *page)
+/* Free whole pageblock */
+void __init init_reserved_pageblock(struct page *page)
 {
 	unsigned i = pageblock_nr_pages;
 	struct page *p = page;
@@ -2314,14 +2313,11 @@ void __init init_cma_reserved_pageblock(struct page *page)
 		set_page_count(p, 0);
 	} while (++p, --i);
 
-	set_pageblock_migratetype(page, MIGRATE_CMA);
 	set_page_refcounted(page);
 	__free_pages(page, pageblock_order);
 
 	adjust_managed_page_count(page, pageblock_nr_pages);
-	page_zone(page)->cma_pages += pageblock_nr_pages;
 }
-#endif
 
 /*
  * The order of subdivision here is critical for the IO subsystem.
-- 
2.25.1

[PATCH v2 6/9] memblock: introduce MEMBLOCK_MOVABLE flag

[Doug Berger]

The MEMBLOCK_MOVABLE flag is introduced to designate a memblock
as only supporting movable allocations by the page allocator.

Signed-off-by: Doug Berger <opendmb@gmail.com>
---
 include/linux/memblock.h |  8 ++++++++
 mm/memblock.c            | 24 ++++++++++++++++++++++++
 2 files changed, 32 insertions(+)

diff --git a/include/linux/memblock.h b/include/linux/memblock.h
index 50ad19662a32..8eb3ca32dfa7 100644
--- a/include/linux/memblock.h
+++ b/include/linux/memblock.h
@@ -47,6 +47,7 @@ enum memblock_flags {
 	MEMBLOCK_MIRROR		= 0x2,	/* mirrored region */
 	MEMBLOCK_NOMAP		= 0x4,	/* don't add to kernel direct mapping */
 	MEMBLOCK_DRIVER_MANAGED = 0x8,	/* always detected via a driver */
+	MEMBLOCK_MOVABLE	= 0x10,	/* designated movable block */
 };
 
 /**
@@ -125,6 +126,8 @@ int memblock_clear_hotplug(phys_addr_t base, phys_addr_t size);
 int memblock_mark_mirror(phys_addr_t base, phys_addr_t size);
 int memblock_mark_nomap(phys_addr_t base, phys_addr_t size);
 int memblock_clear_nomap(phys_addr_t base, phys_addr_t size);
+int memblock_mark_movable(phys_addr_t base, phys_addr_t size);
+int memblock_clear_movable(phys_addr_t base, phys_addr_t size);
 
 void memblock_free_all(void);
 void memblock_free(void *ptr, size_t size);
@@ -265,6 +268,11 @@ static inline bool memblock_is_driver_managed(struct memblock_region *m)
 	return m->flags & MEMBLOCK_DRIVER_MANAGED;
 }
 
+static inline bool memblock_is_movable(struct memblock_region *m)
+{
+	return m->flags & MEMBLOCK_MOVABLE;
+}
+
 int memblock_search_pfn_nid(unsigned long pfn, unsigned long *start_pfn,
 			    unsigned long  *end_pfn);
 void __next_mem_pfn_range(int *idx, int nid, unsigned long *out_start_pfn,
diff --git a/mm/memblock.c b/mm/memblock.c
index b5d3026979fc..5d6a210d98ec 100644
--- a/mm/memblock.c
+++ b/mm/memblock.c
@@ -979,6 +979,30 @@ int __init_memblock memblock_clear_nomap(phys_addr_t base, phys_addr_t size)
 	return memblock_setclr_flag(base, size, 0, MEMBLOCK_NOMAP);
 }
 
+/**
+ * memblock_mark_movable - Mark designated movable block with MEMBLOCK_MOVABLE.
+ * @base: the base phys addr of the region
+ * @size: the size of the region
+ *
+ * Return: 0 on success, -errno on failure.
+ */
+int __init_memblock memblock_mark_movable(phys_addr_t base, phys_addr_t size)
+{
+	return memblock_setclr_flag(base, size, 1, MEMBLOCK_MOVABLE);
+}
+
+/**
+ * memblock_clear_movable - Clear flag MEMBLOCK_MOVABLE for a specified region.
+ * @base: the base phys addr of the region
+ * @size: the size of the region
+ *
+ * Return: 0 on success, -errno on failure.
+ */
+int __init_memblock memblock_clear_movable(phys_addr_t base, phys_addr_t size)
+{
+	return memblock_setclr_flag(base, size, 0, MEMBLOCK_MOVABLE);
+}
+
 static bool should_skip_region(struct memblock_type *type,
 			       struct memblock_region *m,
 			       int nid, int flags)
-- 
2.25.1

[PATCH v2 7/9] mm/dmb: Introduce Designated Movable Blocks

[Doug Berger]

Designated Movable Blocks are blocks of memory that are composed
of one or more adjacent memblocks that have the MEMBLOCK_MOVABLE
designation. These blocks must be reserved before receiving that
designation and will be located in the ZONE_MOVABLE zone rather
than any other zone that may span them.

Signed-off-by: Doug Berger <opendmb@gmail.com>
---
 include/linux/dmb.h | 29 +++++++++++++++
 mm/Kconfig          | 12 ++++++
 mm/Makefile         |  1 +
 mm/dmb.c            | 91 +++++++++++++++++++++++++++++++++++++++++++++
 mm/memblock.c       |  6 ++-
 mm/page_alloc.c     | 84 ++++++++++++++++++++++++++++++++++-------
 6 files changed, 209 insertions(+), 14 deletions(-)
 create mode 100644 include/linux/dmb.h
 create mode 100644 mm/dmb.c

diff --git a/include/linux/dmb.h b/include/linux/dmb.h
new file mode 100644
index 000000000000..fa2976c0fa21
--- /dev/null
+++ b/include/linux/dmb.h
@@ -0,0 +1,29 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef __DMB_H__
+#define __DMB_H__
+
+#include <linux/memblock.h>
+
+/*
+ * the buddy -- especially pageblock merging and alloc_contig_range()
+ * -- can deal with only some pageblocks of a higher-order page being
+ *  MIGRATE_MOVABLE, we can use pageblock_nr_pages.
+ */
+#define DMB_MIN_ALIGNMENT_PAGES pageblock_nr_pages
+#define DMB_MIN_ALIGNMENT_BYTES (PAGE_SIZE * DMB_MIN_ALIGNMENT_PAGES)
+
+enum {
+	DMB_DISJOINT = 0,
+	DMB_INTERSECTS,
+	DMB_MIXED,
+};
+
+struct dmb;
+
+extern int dmb_intersects(unsigned long spfn, unsigned long epfn);
+
+extern int dmb_reserve(phys_addr_t base, phys_addr_t size,
+		       struct dmb **res_dmb);
+extern void dmb_init_region(struct memblock_region *region);
+
+#endif
diff --git a/mm/Kconfig b/mm/Kconfig
index 0331f1461f81..7739edde5d4d 100644
--- a/mm/Kconfig
+++ b/mm/Kconfig
@@ -868,6 +868,18 @@ config CMA_AREAS
 
 	  If unsure, leave the default value "7" in UMA and "19" in NUMA.
 
+config DMB_COUNT
+	int "Maximum count of Designated Movable Blocks"
+	default 19 if NUMA
+	default 7
+	help
+	  Designated Movable Blocks are blocks of memory that can be used
+	  by the page allocator exclusively for movable pages. They are
+	  managed in ZONE_MOVABLE but may overlap with other zones. This
+	  parameter sets the maximum number of DMBs in the system.
+
+	  If unsure, leave the default value "7" in UMA and "19" in NUMA.
+
 config MEM_SOFT_DIRTY
 	bool "Track memory changes"
 	depends on CHECKPOINT_RESTORE && HAVE_ARCH_SOFT_DIRTY && PROC_FS
diff --git a/mm/Makefile b/mm/Makefile
index 9a564f836403..d0b469a494f2 100644
--- a/mm/Makefile
+++ b/mm/Makefile
@@ -67,6 +67,7 @@ obj-y += page-alloc.o
 obj-y += init-mm.o
 obj-y += memblock.o
 obj-y += $(memory-hotplug-y)
+obj-y += dmb.o
 
 ifdef CONFIG_MMU
 	obj-$(CONFIG_ADVISE_SYSCALLS)	+= madvise.o
diff --git a/mm/dmb.c b/mm/dmb.c
new file mode 100644
index 000000000000..f6c4e2662e0f
--- /dev/null
+++ b/mm/dmb.c
@@ -0,0 +1,91 @@
+// SPDX-License-Identifier: GPL-2.0+
+/*
+ * Designated Movable Block
+ */
+
+#define pr_fmt(fmt) "dmb: " fmt
+
+#include <linux/dmb.h>
+
+struct dmb {
+	unsigned long start_pfn;
+	unsigned long end_pfn;
+};
+
+static struct dmb dmb_areas[CONFIG_DMB_COUNT];
+static unsigned int dmb_area_count;
+
+int dmb_intersects(unsigned long spfn, unsigned long epfn)
+{
+	int i;
+	struct dmb *dmb;
+
+	if (spfn >= epfn)
+		return DMB_DISJOINT;
+
+	for (i = 0; i < dmb_area_count; i++) {
+		dmb = &dmb_areas[i];
+		if (spfn >= dmb->end_pfn)
+			continue;
+		if (epfn <= dmb->start_pfn)
+			return DMB_DISJOINT;
+		if (spfn >= dmb->start_pfn && epfn <= dmb->end_pfn)
+			return DMB_INTERSECTS;
+		else
+			return DMB_MIXED;
+	}
+
+	return DMB_DISJOINT;
+}
+EXPORT_SYMBOL(dmb_intersects);
+
+int __init dmb_reserve(phys_addr_t base, phys_addr_t size,
+		       struct dmb **res_dmb)
+{
+	struct dmb *dmb;
+
+	/* Sanity checks */
+	if (!size || !memblock_is_region_reserved(base, size))
+		return -EINVAL;
+
+	/* ensure minimal alignment required by mm core */
+	if (!IS_ALIGNED(base | size, DMB_MIN_ALIGNMENT_BYTES))
+		return -EINVAL;
+
+	if (dmb_area_count == ARRAY_SIZE(dmb_areas)) {
+		pr_warn("Not enough slots for DMB reserved regions!\n");
+		return -ENOSPC;
+	}
+
+	/*
+	 * Each reserved area must be initialised later, when more kernel
+	 * subsystems (like slab allocator) are available.
+	 */
+	dmb = &dmb_areas[dmb_area_count++];
+
+	dmb->start_pfn = PFN_DOWN(base);
+	dmb->end_pfn = PFN_DOWN(base + size);
+	if (res_dmb)
+		*res_dmb = dmb;
+
+	memblock_mark_movable(base, size);
+	return 0;
+}
+
+void __init dmb_init_region(struct memblock_region *region)
+{
+	unsigned long pfn;
+	int i;
+
+	for (pfn = memblock_region_memory_base_pfn(region);
+	     pfn < memblock_region_memory_end_pfn(region);
+	     pfn += pageblock_nr_pages) {
+		struct page *page = pfn_to_page(pfn);
+
+		for (i = 0; i < pageblock_nr_pages; i++)
+			set_page_zone(page + i, ZONE_MOVABLE);
+
+		/* free reserved pageblocks to page allocator */
+		init_reserved_pageblock(page);
+	}
+}
diff --git a/mm/memblock.c b/mm/memblock.c
index 5d6a210d98ec..9eb91acdeb75 100644
--- a/mm/memblock.c
+++ b/mm/memblock.c
@@ -16,6 +16,7 @@
 #include <linux/kmemleak.h>
 #include <linux/seq_file.h>
 #include <linux/memblock.h>
+#include <linux/dmb.h>
 
 #include <asm/sections.h>
 #include <linux/io.h>
@@ -2090,13 +2091,16 @@ static void __init memmap_init_reserved_pages(void)
 	for_each_reserved_mem_range(i, &start, &end)
 		reserve_bootmem_region(start, end);
 
-	/* and also treat struct pages for the NOMAP regions as PageReserved */
 	for_each_mem_region(region) {
+		/* treat struct pages for the NOMAP regions as PageReserved */
 		if (memblock_is_nomap(region)) {
 			start = region->base;
 			end = start + region->size;
 			reserve_bootmem_region(start, end);
 		}
+		/* move Designated Movable Block pages to ZONE_MOVABLE */
+		if (memblock_is_movable(region))
+			dmb_init_region(region);
 	}
 }
 
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 6d4470b0daba..cd31f26b0d21 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -75,6 +75,7 @@
 #include <linux/khugepaged.h>
 #include <linux/buffer_head.h>
 #include <linux/delayacct.h>
+#include <linux/dmb.h>
 #include <asm/sections.h>
 #include <asm/tlbflush.h>
 #include <asm/div64.h>
@@ -433,6 +434,7 @@ static unsigned long required_kernelcore __initdata;
 static unsigned long required_kernelcore_percent __initdata;
 static unsigned long required_movablecore __initdata;
 static unsigned long required_movablecore_percent __initdata;
+static unsigned long min_dmb_pfn[MAX_NUMNODES] __initdata;
 static unsigned long zone_movable_pfn[MAX_NUMNODES] __initdata;
 bool mirrored_kernelcore __initdata_memblock;
 
@@ -2165,7 +2167,7 @@ static int __init deferred_init_memmap(void *data)
 	}
 zone_empty:
 	/* Sanity check that the next zone really is unpopulated */
-	WARN_ON(++zid < MAX_NR_ZONES && populated_zone(++zone));
+	WARN_ON(++zid < ZONE_MOVABLE && populated_zone(++zone));
 
 	pr_info("node %d deferred pages initialised in %ums\n",
 		pgdat->node_id, jiffies_to_msecs(jiffies - start));
@@ -6899,6 +6901,10 @@ static void __init memmap_init_zone_range(struct zone *zone,
 	unsigned long zone_end_pfn = zone_start_pfn + zone->spanned_pages;
 	int nid = zone_to_nid(zone), zone_id = zone_idx(zone);
 
+	/* Skip overlap of ZONE_MOVABLE */
+	if (zone_id == ZONE_MOVABLE && zone_start_pfn < *hole_pfn)
+		zone_start_pfn = *hole_pfn;
+
 	start_pfn = clamp(start_pfn, zone_start_pfn, zone_end_pfn);
 	end_pfn = clamp(end_pfn, zone_start_pfn, zone_end_pfn);
 
@@ -7348,6 +7354,9 @@ static unsigned long __init zone_spanned_pages_in_node(int nid,
 				node_start_pfn, node_end_pfn,
 				zone_start_pfn, zone_end_pfn);
 
+	if (zone_type == ZONE_MOVABLE && min_dmb_pfn[nid])
+		*zone_start_pfn = min(*zone_start_pfn, min_dmb_pfn[nid]);
+
 	/* Check that this node has pages within the zone's required range */
 	if (*zone_end_pfn < node_start_pfn || *zone_start_pfn > node_end_pfn)
 		return 0;
@@ -7416,12 +7425,17 @@ static unsigned long __init zone_absent_pages_in_node(int nid,
 			&zone_start_pfn, &zone_end_pfn);
 	nr_absent = __absent_pages_in_range(nid, zone_start_pfn, zone_end_pfn);
 
+	if (zone_type == ZONE_MOVABLE && min_dmb_pfn[nid]) {
+		zone_start_pfn = min(zone_start_pfn, min_dmb_pfn[nid]);
+		nr_absent += zone_movable_pfn[nid] - zone_start_pfn;
+	}
+
 	/*
 	 * ZONE_MOVABLE handling.
-	 * Treat pages to be ZONE_MOVABLE in ZONE_NORMAL as absent pages
+	 * Treat pages to be ZONE_MOVABLE in other zones as absent pages
 	 * and vice versa.
 	 */
-	if (mirrored_kernelcore && zone_movable_pfn[nid]) {
+	if (zone_movable_pfn[nid]) {
 		unsigned long start_pfn, end_pfn;
 		struct memblock_region *r;
 
@@ -7431,6 +7445,21 @@ static unsigned long __init zone_absent_pages_in_node(int nid,
 			end_pfn = clamp(memblock_region_memory_end_pfn(r),
 					zone_start_pfn, zone_end_pfn);
 
+			if (memblock_is_movable(r)) {
+				if (zone_type != ZONE_MOVABLE) {
+					nr_absent += end_pfn - start_pfn;
+					continue;
+				}
+
+				end_pfn = min(end_pfn, zone_movable_pfn[nid]);
+				if (start_pfn < zone_movable_pfn[nid])
+					nr_absent -=  end_pfn - start_pfn;
+				continue;
+			}
+
+			if (!mirrored_kernelcore)
+				continue;
+
 			if (zone_type == ZONE_MOVABLE &&
 			    memblock_is_mirror(r))
 				nr_absent += end_pfn - start_pfn;
@@ -7450,6 +7479,15 @@ static void __init calculate_node_totalpages(struct pglist_data *pgdat,
 {
 	unsigned long realtotalpages = 0;
 	enum zone_type i;
+	int nid = pgdat->node_id;
+
+	/*
+	 * If Designated Movable Blocks are defined on this node, ensure that
+	 * zone_movable_pfn is also defined for this node.
+	 */
+	if (min_dmb_pfn[nid] && !zone_movable_pfn[nid])
+		zone_movable_pfn[nid] = min(node_end_pfn,
+				arch_zone_highest_possible_pfn[movable_zone]);
 
 	for (i = 0; i < MAX_NR_ZONES; i++) {
 		struct zone *zone = pgdat->node_zones + i;
@@ -7457,12 +7495,12 @@ static void __init calculate_node_totalpages(struct pglist_data *pgdat,
 		unsigned long spanned, absent;
 		unsigned long size, real_size;
 
-		spanned = zone_spanned_pages_in_node(pgdat->node_id, i,
+		spanned = zone_spanned_pages_in_node(nid, i,
 						     node_start_pfn,
 						     node_end_pfn,
 						     &zone_start_pfn,
 						     &zone_end_pfn);
-		absent = zone_absent_pages_in_node(pgdat->node_id, i,
+		absent = zone_absent_pages_in_node(nid, i,
 						   node_start_pfn,
 						   node_end_pfn);
 
@@ -7922,15 +7960,23 @@ unsigned long __init find_min_pfn_with_active_regions(void)
 static unsigned long __init early_calculate_totalpages(void)
 {
 	unsigned long totalpages = 0;
-	unsigned long start_pfn, end_pfn;
-	int i, nid;
+	struct memblock_region *r;
 
-	for_each_mem_pfn_range(i, MAX_NUMNODES, &start_pfn, &end_pfn, &nid) {
-		unsigned long pages = end_pfn - start_pfn;
+	for_each_mem_region(r) {
+		unsigned long start_pfn, end_pfn, pages;
+		int nid;
 
-		totalpages += pages;
-		if (pages)
+		nid = memblock_get_region_node(r);
+		start_pfn = memblock_region_memory_base_pfn(r);
+		end_pfn = memblock_region_memory_end_pfn(r);
+
+		pages = end_pfn - start_pfn;
+		if (pages) {
+			totalpages += pages;
 			node_set_state(nid, N_MEMORY);
+			if (memblock_is_movable(r) && !min_dmb_pfn[nid])
+				min_dmb_pfn[nid] = start_pfn;
+		}
 	}
 	return totalpages;
 }
@@ -7943,7 +7989,7 @@ static unsigned long __init early_calculate_totalpages(void)
  */
 static void __init find_zone_movable_pfns_for_nodes(void)
 {
-	int i, nid;
+	int nid;
 	unsigned long usable_startpfn;
 	unsigned long kernelcore_node, kernelcore_remaining;
 	/* save the state before borrow the nodemask */
@@ -8071,13 +8117,24 @@ static void __init find_zone_movable_pfns_for_nodes(void)
 		kernelcore_remaining = kernelcore_node;
 
 		/* Go through each range of PFNs within this node */
-		for_each_mem_pfn_range(i, nid, &start_pfn, &end_pfn, NULL) {
+		for_each_mem_region(r) {
 			unsigned long size_pages;
 
+			if (memblock_get_region_node(r) != nid)
+				continue;
+
+			start_pfn = memblock_region_memory_base_pfn(r);
+			end_pfn = memblock_region_memory_end_pfn(r);
 			start_pfn = max(start_pfn, zone_movable_pfn[nid]);
 			if (start_pfn >= end_pfn)
 				continue;
 
+			/* Skip over Designated Movable Blocks */
+			if (memblock_is_movable(r)) {
+				zone_movable_pfn[nid] = end_pfn;
+				continue;
+			}
+
 			/* Account for what is only usable for kernelcore */
 			if (start_pfn < usable_startpfn) {
 				unsigned long kernel_pages;
@@ -8226,6 +8283,7 @@ void __init free_area_init(unsigned long *max_zone_pfn)
 	}
 
 	/* Find the PFNs that ZONE_MOVABLE begins at in each node */
+	memset(min_dmb_pfn, 0, sizeof(min_dmb_pfn));
 	memset(zone_movable_pfn, 0, sizeof(zone_movable_pfn));
 	find_zone_movable_pfns_for_nodes();
 
-- 
2.25.1

[PATCH v2 8/9] mm/page_alloc: make alloc_contig_pages DMB aware

[Doug Berger]

Designated Movable Blocks are skipped when attempting to allocate
contiguous pages. Doing per page validation across all spanned
pages within a zone can be extra inefficient when Designated
Movable Blocks create large overlaps between zones. Use
dmb_intersects() within pfn_range_valid_contig as an early check
to signal the range is not valid.

The zone_movable_pfn array which represents the start of non-
overlapped ZONE_MOVABLE on the node is now preserved to be used
at runtime to skip over any DMB-only portion of the zone.

Signed-off-by: Doug Berger <opendmb@gmail.com>
---
 mm/page_alloc.c | 10 ++++++++--
 1 file changed, 8 insertions(+), 2 deletions(-)

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index cd31f26b0d21..c07111a897c0 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -435,7 +435,7 @@ static unsigned long required_kernelcore_percent __initdata;
 static unsigned long required_movablecore __initdata;
 static unsigned long required_movablecore_percent __initdata;
 static unsigned long min_dmb_pfn[MAX_NUMNODES] __initdata;
-static unsigned long zone_movable_pfn[MAX_NUMNODES] __initdata;
+static unsigned long zone_movable_pfn[MAX_NUMNODES];
 bool mirrored_kernelcore __initdata_memblock;
 
 /* movable_zone is the "real" zone pages in ZONE_MOVABLE are taken from */
@@ -9369,6 +9369,9 @@ static bool pfn_range_valid_contig(struct zone *z, unsigned long start_pfn,
 	unsigned long i, end_pfn = start_pfn + nr_pages;
 	struct page *page;
 
+	if (dmb_intersects(start_pfn, end_pfn))
+		return false;
+
 	for (i = start_pfn; i < end_pfn; i++) {
 		page = pfn_to_online_page(i);
 		if (!page)
@@ -9425,7 +9428,10 @@ struct page *alloc_contig_pages(unsigned long nr_pages, gfp_t gfp_mask,
 					gfp_zone(gfp_mask), nodemask) {
 		spin_lock_irqsave(&zone->lock, flags);
 
-		pfn = ALIGN(zone->zone_start_pfn, nr_pages);
+		if (zone_idx(zone) == ZONE_MOVABLE && zone_movable_pfn[nid])
+			pfn = ALIGN(zone_movable_pfn[nid], nr_pages);
+		else
+			pfn = ALIGN(zone->zone_start_pfn, nr_pages);
 		while (zone_spans_last_pfn(zone, pfn, nr_pages)) {
 			if (pfn_range_valid_contig(zone, pfn, nr_pages)) {
 				/*
-- 
2.25.1

[PATCH v2 9/9] mm/page_alloc: allow base for movablecore

[Doug Berger]

A Designated Movable Block can be created by including the base
address of the block when specifying a movablecore range on the
kernel command line.

Signed-off-by: Doug Berger <opendmb@gmail.com>
---
 .../admin-guide/kernel-parameters.txt         | 14 ++++++-
 mm/page_alloc.c                               | 38 ++++++++++++++++---
 2 files changed, 45 insertions(+), 7 deletions(-)

diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index 426fa892d311..8141fac7c7cb 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -3312,7 +3312,7 @@
 			reporting absolute coordinates, such as tablets
 
 	movablecore=	[KNL,X86,IA-64,PPC]
-			Format: nn[KMGTPE] | nn%
+			Format: nn[KMGTPE] | nn[KMGTPE]@ss[KMGTPE] | nn%
 			This parameter is the complement to kernelcore=, it
 			specifies the amount of memory used for migratable
 			allocations.  If both kernelcore and movablecore is
@@ -3322,6 +3322,18 @@
 			that the amount of memory usable for all allocations
 			is not too small.
 
+			If @ss[KMGTPE] is included, memory within the region
+			from ss to ss+nn will be designated as a movable block
+			and included in ZONE_MOVABLE. Designated Movable Blocks
+			must be aligned to pageblock_order. Designated Movable
+			Blocks take priority over values of kernelcore= and are
+			considered part of any memory specified by more general
+			movablecore= values.
+			Multiple Designated Movable Blocks may be specified,
+			comma delimited.
+			Example:
+				movablecore=100M@2G,100M@3G,1G@1024G
+
 	movable_node	[KNL] Boot-time switch to make hotplugable memory
 			NUMA nodes to be movable. This means that the memory
 			of such nodes will be usable only for movable
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index c07111a897c0..a151752c4266 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -8370,9 +8370,9 @@ void __init free_area_init(unsigned long *max_zone_pfn)
 }
 
 static int __init cmdline_parse_core(char *p, unsigned long *core,
-				     unsigned long *percent)
+				     unsigned long *percent, bool movable)
 {
-	unsigned long long coremem;
+	unsigned long long coremem, address;
 	char *endptr;
 
 	if (!p)
@@ -8387,6 +8387,17 @@ static int __init cmdline_parse_core(char *p, unsigned long *core,
 		*percent = coremem;
 	} else {
 		coremem = memparse(p, &p);
+		if (movable && *p == '@') {
+			address = memparse(++p, &p);
+			if (*p != '\0' ||
+			    !memblock_is_region_memory(address, coremem) ||
+			    memblock_is_region_reserved(address, coremem))
+				return -EINVAL;
+			memblock_reserve(address, coremem);
+			return dmb_reserve(address, coremem, NULL);
+		} else if (*p != '\0') {
+			return -EINVAL;
+		}
 		/* Paranoid check that UL is enough for the coremem value */
 		WARN_ON((coremem >> PAGE_SHIFT) > ULONG_MAX);
 
@@ -8409,17 +8420,32 @@ static int __init cmdline_parse_kernelcore(char *p)
 	}
 
 	return cmdline_parse_core(p, &required_kernelcore,
-				  &required_kernelcore_percent);
+				  &required_kernelcore_percent, false);
 }
 
 /*
  * movablecore=size sets the amount of memory for use for allocations that
- * can be reclaimed or migrated.
+ * can be reclaimed or migrated. movablecore=size@base defines a Designated
+ * Movable Block.
  */
 static int __init cmdline_parse_movablecore(char *p)
 {
-	return cmdline_parse_core(p, &required_movablecore,
-				  &required_movablecore_percent);
+	int ret = -EINVAL;
+
+	while (p) {
+		char *k = strchr(p, ',');
+
+		if (k)
+			*k++ = 0;
+
+		ret = cmdline_parse_core(p, &required_movablecore,
+					 &required_movablecore_percent, true);
+		if (ret)
+			break;
+		p = k;
+	}
+
+	return ret;
 }
 
 early_param("kernelcore", cmdline_parse_kernelcore);
-- 
2.25.1

Re: [PATCH v2 2/9] mm/vmstat: show start_pfn when zone spans pages

[David Hildenbrand]

On 29.09.22 00:32, Doug Berger wrote:
> A zone that overlaps with another zone may span a range of pages
> that are not present. In this case, displaying the start_pfn of
> the zone allows the zone page range to be identified.
> 

I don't understand the intention here.

"/* If unpopulated, no other information is useful */"

Why would the start pfn be of any use here?

What is the user visible impact without that change?

> Signed-off-by: Doug Berger <opendmb@gmail.com>
> ---
>   mm/vmstat.c | 5 +++++
>   1 file changed, 5 insertions(+)
> 
> diff --git a/mm/vmstat.c b/mm/vmstat.c
> index 90af9a8572f5..e2f19f2b7615 100644
> --- a/mm/vmstat.c
> +++ b/mm/vmstat.c
> @@ -1717,6 +1717,11 @@ static void zoneinfo_show_print(struct seq_file *m, pg_data_t *pgdat,
>   
>   	/* If unpopulated, no other information is useful */
>   	if (!populated_zone(zone)) {
> +		/* Show start_pfn for empty overlapped zones */
> +		if (zone->spanned_pages)
> +			seq_printf(m,
> +				   "\n  start_pfn:           %lu",
> +				   zone->zone_start_pfn);
>   		seq_putc(m, '\n');
>   		return;
>   	}
-- 
Thanks,

David / dhildenb

Re: [PATCH v2 2/9] mm/vmstat: show start_pfn when zone spans pages

[Doug Berger]

On 9/29/2022 1:15 AM, David Hildenbrand wrote:
> On 29.09.22 00:32, Doug Berger wrote:
>> A zone that overlaps with another zone may span a range of pages
>> that are not present. In this case, displaying the start_pfn of
>> the zone allows the zone page range to be identified.
>>
> 
> I don't understand the intention here.
> 
> "/* If unpopulated, no other information is useful */"
> 
> Why would the start pfn be of any use here?
> 
> What is the user visible impact without that change?
Yes, this is very subtle. I only caught it while testing some 
pathological cases.

If you take the example system:
The 7278 device has four ARMv8 CPU cores in an SMP cluster and two 
memory controllers (MEMCs). Each MEMC is capable of controlling up to 
8GB of DRAM. An example 7278 system might have 1GB on each controller, 
so an arm64 kernel might see 1GB on MEMC0 at 0x40000000-0x7FFFFFFF and 
1GB on MEMC1 at 0x300000000-0x33FFFFFFF.

Placing a DMB on MEMC0 with 'movablecore=256M@0x70000000' will lead to 
the ZONE_MOVABLE zone spanning from 0x70000000-0x33fffffff and the 
ZONE_NORMAL zone spanning from 0x300000000-0x33fffffff.

If instead you specified 'movablecore=256M@0x70000000,512M' you would 
get the same ZONE_MOVABLE span, but the ZONE_NORMAL would now span 
0x300000000-0x32fffffff. The requested 512M of movablecore would be 
divided into a 256MB DMB at 0x70000000 and a 256MB "classic" movable 
zone start would be displayed in the bootlog as:
[    0.000000] Movable zone start for each node
[    0.000000]   Node 0: 0x000000330000000

Finally, if you specified the pathological 
'movablecore=256M@0x70000000,1G@12G' you would still have the same 
ZONE_MOVABLE span, and the ZONE_NORMAL span would go back to 
0x300000000-0x33fffffff. However, because the second DMB (1G@12G) 
completely overlaps the ZONE_NORMAL there would be no pages present in 
ZONE_NORMAL and /proc/zoneinfo would report ZONE_NORMAL 'spanned 
262144', but not where those pages are. This commit adds the 'start_pfn' 
back to the /proc/zoneinfo for ZONE_NORMAL so the span has context.

Regards,
     Doug

> 
>> Signed-off-by: Doug Berger <opendmb@gmail.com>
>> ---
>>   mm/vmstat.c | 5 +++++
>>   1 file changed, 5 insertions(+)
>>
>> diff --git a/mm/vmstat.c b/mm/vmstat.c
>> index 90af9a8572f5..e2f19f2b7615 100644
>> --- a/mm/vmstat.c
>> +++ b/mm/vmstat.c
>> @@ -1717,6 +1717,11 @@ static void zoneinfo_show_print(struct seq_file 
>> *m, pg_data_t *pgdat,
>>       /* If unpopulated, no other information is useful */
>>       if (!populated_zone(zone)) {
>> +        /* Show start_pfn for empty overlapped zones */
>> +        if (zone->spanned_pages)
>> +            seq_printf(m,
>> +                   "\n  start_pfn:           %lu",
>> +                   zone->zone_start_pfn);
>>           seq_putc(m, '\n');
>>           return;
>>       }

Re: [PATCH v2 2/9] mm/vmstat: show start_pfn when zone spans pages

[David Hildenbrand]

On 01.10.22 03:28, Doug Berger wrote:
> On 9/29/2022 1:15 AM, David Hildenbrand wrote:
>> On 29.09.22 00:32, Doug Berger wrote:
>>> A zone that overlaps with another zone may span a range of pages
>>> that are not present. In this case, displaying the start_pfn of
>>> the zone allows the zone page range to be identified.
>>>
>>
>> I don't understand the intention here.
>>
>> "/* If unpopulated, no other information is useful */"
>>
>> Why would the start pfn be of any use here?
>>
>> What is the user visible impact without that change?
> Yes, this is very subtle. I only caught it while testing some
> pathological cases.
> 
> If you take the example system:
> The 7278 device has four ARMv8 CPU cores in an SMP cluster and two
> memory controllers (MEMCs). Each MEMC is capable of controlling up to
> 8GB of DRAM. An example 7278 system might have 1GB on each controller,
> so an arm64 kernel might see 1GB on MEMC0 at 0x40000000-0x7FFFFFFF and
> 1GB on MEMC1 at 0x300000000-0x33FFFFFFF.
> 

Okay, thanks. You should make it clearer in the patch description -- 
especially how this relates to DMB. Having that said, I still have to 
digest your examples:

> Placing a DMB on MEMC0 with 'movablecore=256M@0x70000000' will lead to
> the ZONE_MOVABLE zone spanning from 0x70000000-0x33fffffff and the
> ZONE_NORMAL zone spanning from 0x300000000-0x33fffffff.

Why is ZONE_MOVABLE spanning more than 256M? It should span

0x70000000-0x80000000

Or what am I missing?

> 
> If instead you specified 'movablecore=256M@0x70000000,512M' you would
> get the same ZONE_MOVABLE span, but the ZONE_NORMAL would now span
> 0x300000000-0x32fffffff. The requested 512M of movablecore would be
> divided into a 256MB DMB at 0x70000000 and a 256MB "classic" movable
> zone start would be displayed in the bootlog as:
> [    0.000000] Movable zone start for each node
> [    0.000000]   Node 0: 0x000000330000000


Okay, so that's the movable zone range excluding DMB.

> 
> Finally, if you specified the pathological
> 'movablecore=256M@0x70000000,1G@12G' you would still have the same
> ZONE_MOVABLE span, and the ZONE_NORMAL span would go back to
> 0x300000000-0x33fffffff. However, because the second DMB (1G@12G)
> completely overlaps the ZONE_NORMAL there would be no pages present in
> ZONE_NORMAL and /proc/zoneinfo would report ZONE_NORMAL 'spanned
> 262144', but not where those pages are. This commit adds the 'start_pfn'
> back to the /proc/zoneinfo for ZONE_NORMAL so the span has context.

... but why? If there are no pages present, there is no ZONE_NORMAL we 
care about. The zone span should be 0. Does this maybe rather indicate 
that there is a zone span processing issue in your DMB implementation?

Special-casing zones based on DMBs feels wrong. But most probably I am 
missing something important :)

-- 
Thanks,

David / dhildenb

Re: [PATCH v2 2/9] mm/vmstat: show start_pfn when zone spans pages

[Doug Berger]

On 10/5/2022 11:09 AM, David Hildenbrand wrote:
> On 01.10.22 03:28, Doug Berger wrote:
>> On 9/29/2022 1:15 AM, David Hildenbrand wrote:
>>> On 29.09.22 00:32, Doug Berger wrote:
>>>> A zone that overlaps with another zone may span a range of pages
>>>> that are not present. In this case, displaying the start_pfn of
>>>> the zone allows the zone page range to be identified.
>>>>
>>>
>>> I don't understand the intention here.
>>>
>>> "/* If unpopulated, no other information is useful */"
>>>
>>> Why would the start pfn be of any use here?
>>>
>>> What is the user visible impact without that change?
>> Yes, this is very subtle. I only caught it while testing some
>> pathological cases.
>>
>> If you take the example system:
>> The 7278 device has four ARMv8 CPU cores in an SMP cluster and two
>> memory controllers (MEMCs). Each MEMC is capable of controlling up to
>> 8GB of DRAM. An example 7278 system might have 1GB on each controller,
>> so an arm64 kernel might see 1GB on MEMC0 at 0x40000000-0x7FFFFFFF and
>> 1GB on MEMC1 at 0x300000000-0x33FFFFFFF.
>>
> 
> Okay, thanks. You should make it clearer in the patch description -- 
> especially how this relates to DMB. Having that said, I still have to 
> digest your examples:
> 
>> Placing a DMB on MEMC0 with 'movablecore=256M@0x70000000' will lead to
>> the ZONE_MOVABLE zone spanning from 0x70000000-0x33fffffff and the
>> ZONE_NORMAL zone spanning from 0x300000000-0x33fffffff.
> 
> Why is ZONE_MOVABLE spanning more than 256M? It should span
> 
> 0x70000000-0x80000000
> 
> Or what am I missing?
I was working from the notion that the classic 'movablecore' 
implementation keeps the ZONE_MOVABLE zone the last zone on System RAM 
so it always spans the last page on the node (i.e. 0x33ffff000). My 
implementation moves the start of ZONE_MOVABLE up to the lowest page of 
any defined DMBs on the node.

I see that memory hotplug does not behave this way, which is probably 
more intuitive (though less consistent with the classic zone layout). I 
could attempt to change this in a v3 if desired.

> 
>>
>> If instead you specified 'movablecore=256M@0x70000000,512M' you would
>> get the same ZONE_MOVABLE span, but the ZONE_NORMAL would now span
>> 0x300000000-0x32fffffff. The requested 512M of movablecore would be
>> divided into a 256MB DMB at 0x70000000 and a 256MB "classic" movable
>> zone start would be displayed in the bootlog as:
>> [    0.000000] Movable zone start for each node
>> [    0.000000]   Node 0: 0x000000330000000
> 
> 
> Okay, so that's the movable zone range excluding DMB.
> 
>>
>> Finally, if you specified the pathological
>> 'movablecore=256M@0x70000000,1G@12G' you would still have the same
>> ZONE_MOVABLE span, and the ZONE_NORMAL span would go back to
>> 0x300000000-0x33fffffff. However, because the second DMB (1G@12G)
>> completely overlaps the ZONE_NORMAL there would be no pages present in
>> ZONE_NORMAL and /proc/zoneinfo would report ZONE_NORMAL 'spanned
>> 262144', but not where those pages are. This commit adds the 'start_pfn'
>> back to the /proc/zoneinfo for ZONE_NORMAL so the span has context.
> 
> ... but why? If there are no pages present, there is no ZONE_NORMAL we 
> care about. The zone span should be 0. Does this maybe rather indicate 
> that there is a zone span processing issue in your DMB implementation?
My implementation uses the zones created by the classic 'movablecore' 
behavior and relocates the pages within DMBs. In this case the 
ZONE_NORMAL still has a span which gets output but no present pages so 
the output didn't show where the zone was without this patch. This is a 
convenience to avoid adding zone resizing and destruction logic outside 
of memory hotplug support, but I could attempt to add that code in a v3 
if desired.

> 
> Special-casing zones based on DMBs feels wrong. But most probably I am 
> missing something important :)
> 

Thanks for making me aware of your confusion so I can attempt to make it 
clearer.
-Doug

Re: [PATCH v2 2/9] mm/vmstat: show start_pfn when zone spans pages

[Michal Hocko]

On Wed 12-10-22 16:57:53, Doug Berger wrote:
[...]
> I was working from the notion that the classic 'movablecore' implementation
> keeps the ZONE_MOVABLE zone the last zone on System RAM so it always spans
> the last page on the node (i.e. 0x33ffff000). My implementation moves the
> start of ZONE_MOVABLE up to the lowest page of any defined DMBs on the node.

I wouldn't rely on movablecore specific implementation. ZONE_MOVABLE can
span any physical address range. ZONE_NORMAL usually covers any ranges
not covered by more specific zones like ZONE_DMA{32}. At least on most
architectures I am familiar with.
-- 
Michal Hocko
SUSE Labs