[PATCH v4 0/3] Fixes for memmap accounting

[PATCH v4 0/3] Fixes for memmap accounting

[Pasha Tatashin]

Memmap accounting provides us with observability of how much memory is
used for per-page metadata: i.e. "struct page"'s and "struct page_ext".
It also provides with information of how much was allocated using
boot allocator (i.e. not part of MemTotal), and how much was allocated
using buddy allocated (i.e. part of MemTotal).

This small series fixes a few problems that were discovered with the
original patch.

Changes:
- Removed patch 'mm: update the memmap stat before page is freed', as
  noticed by Yosry after 3/3 that patch is not needed anymore.
- renamed nr_memmap to nr_mammp_pages and nr_memmap_boot to
  nr_memmap_boot_pages as suggested by David Hildenbrand
- Added the origianl oops information as suggested by Alison Schofield
- Improved commit log message as suggested by David Hildenbrand
- Added review-by's, acked-by's, and tested-by's

v3:
https://lore.kernel.org/linux-mm/20240808154237.220029-1-pasha.tatashin@soleen.com

Pasha Tatashin (3):
  mm: don't account memmap on failure
  mm: add system wide stats items category
  mm: don't account memmap per-node

 include/linux/mmzone.h |  2 --
 include/linux/vmstat.h | 22 +++++++-----------
 mm/hugetlb_vmemmap.c   | 13 +++++------
 mm/mm_init.c           |  3 +--
 mm/page_alloc.c        |  1 -
 mm/page_ext.c          | 18 ++++-----------
 mm/sparse-vmemmap.c    | 11 ++++-----
 mm/sparse.c            |  5 ++---
 mm/vmstat.c            | 51 ++++++++++++++++++++----------------------
 9 files changed, 48 insertions(+), 78 deletions(-)

-- 
2.46.0.76.ge559c4bf1a-goog

[PATCH v4 1/3] mm: don't account memmap on failure

[Pasha Tatashin]

When we fail to allocate the mmemmap in alloc_vmemmap_page_list(), do
not account any already-allocated pages: we're going to free all them
before we return from the function.

Fixes: 15995a352474 ("mm: report per-page metadata information")
Signed-off-by: Pasha Tatashin <pasha.tatashin@soleen.com>
Reviewed-by: Fan Ni <fan.ni@samsung.com>
Reviewed-by: Yosry Ahmed <yosryahmed@google.com>
Acked-by: David Hildenbrand <david@redhat.com>
---
 mm/hugetlb_vmemmap.c | 5 +----
 1 file changed, 1 insertion(+), 4 deletions(-)

diff --git a/mm/hugetlb_vmemmap.c b/mm/hugetlb_vmemmap.c
index 829112b0a914..4f51e0596197 100644
--- a/mm/hugetlb_vmemmap.c
+++ b/mm/hugetlb_vmemmap.c
@@ -392,13 +392,10 @@ static int alloc_vmemmap_page_list(unsigned long start, unsigned long end,
 
 	for (i = 0; i < nr_pages; i++) {
 		page = alloc_pages_node(nid, gfp_mask, 0);
-		if (!page) {
-			mod_node_page_state(NODE_DATA(nid), NR_MEMMAP, i);
+		if (!page)
 			goto out;
-		}
 		list_add(&page->lru, list);
 	}
-
 	mod_node_page_state(NODE_DATA(nid), NR_MEMMAP, nr_pages);
 
 	return 0;
-- 
2.46.0.76.ge559c4bf1a-goog

[PATCH v4 2/3] mm: add system wide stats items category

[Pasha Tatashin]

/proc/vmstat contains events and stats, events can only grow, but stats
can grow and shrink.

vmstat has the following:
-------------------------
NR_VM_ZONE_STAT_ITEMS:	per-zone stats
NR_VM_NUMA_EVENT_ITEMS:	per-numa events
NR_VM_NODE_STAT_ITEMS:	per-numa stats
NR_VM_WRITEBACK_STAT_ITEMS:	system-wide background-writeback and
				dirty-throttling tresholds.
NR_VM_EVENT_ITEMS:	system-wide events
-------------------------

Rename NR_VM_WRITEBACK_STAT_ITEMS to NR_VM_STAT_ITEMS, to track the
system-wide stats, we are going to add per-page metadata stats to this
category in the next patch.

Also delete unused writeback_stat_name() function.

Suggested-by: Yosry Ahmed <yosryahmed@google.com>
Signed-off-by: Pasha Tatashin <pasha.tatashin@soleen.com>
---
 include/linux/vmstat.h | 15 ++++-----------
 mm/vmstat.c            |  6 +++---
 2 files changed, 7 insertions(+), 14 deletions(-)

diff --git a/include/linux/vmstat.h b/include/linux/vmstat.h
index 23cd17942036..9ab4fa5e09b5 100644
--- a/include/linux/vmstat.h
+++ b/include/linux/vmstat.h
@@ -34,10 +34,11 @@ struct reclaim_stat {
 	unsigned nr_lazyfree_fail;
 };
 
-enum writeback_stat_item {
+/* Stat data for system wide items */
+enum vm_stat_item {
 	NR_DIRTY_THRESHOLD,
 	NR_DIRTY_BG_THRESHOLD,
-	NR_VM_WRITEBACK_STAT_ITEMS,
+	NR_VM_STAT_ITEMS,
 };
 
 #ifdef CONFIG_VM_EVENT_COUNTERS
@@ -514,21 +515,13 @@ static inline const char *lru_list_name(enum lru_list lru)
 	return node_stat_name(NR_LRU_BASE + lru) + 3; // skip "nr_"
 }
 
-static inline const char *writeback_stat_name(enum writeback_stat_item item)
-{
-	return vmstat_text[NR_VM_ZONE_STAT_ITEMS +
-			   NR_VM_NUMA_EVENT_ITEMS +
-			   NR_VM_NODE_STAT_ITEMS +
-			   item];
-}
-
 #if defined(CONFIG_VM_EVENT_COUNTERS) || defined(CONFIG_MEMCG)
 static inline const char *vm_event_name(enum vm_event_item item)
 {
 	return vmstat_text[NR_VM_ZONE_STAT_ITEMS +
 			   NR_VM_NUMA_EVENT_ITEMS +
 			   NR_VM_NODE_STAT_ITEMS +
-			   NR_VM_WRITEBACK_STAT_ITEMS +
+			   NR_VM_STAT_ITEMS +
 			   item];
 }
 #endif /* CONFIG_VM_EVENT_COUNTERS || CONFIG_MEMCG */
diff --git a/mm/vmstat.c b/mm/vmstat.c
index 04a1cb6cc636..6f8aa4766f16 100644
--- a/mm/vmstat.c
+++ b/mm/vmstat.c
@@ -1257,7 +1257,7 @@ const char * const vmstat_text[] = {
 	"pgdemote_khugepaged",
 	"nr_memmap",
 	"nr_memmap_boot",
-	/* enum writeback_stat_item counters */
+	/* system-wide enum vm_stat_item counters */
 	"nr_dirty_threshold",
 	"nr_dirty_background_threshold",
 
@@ -1790,7 +1790,7 @@ static const struct seq_operations zoneinfo_op = {
 #define NR_VMSTAT_ITEMS (NR_VM_ZONE_STAT_ITEMS + \
 			 NR_VM_NUMA_EVENT_ITEMS + \
 			 NR_VM_NODE_STAT_ITEMS + \
-			 NR_VM_WRITEBACK_STAT_ITEMS + \
+			 NR_VM_STAT_ITEMS + \
 			 (IS_ENABLED(CONFIG_VM_EVENT_COUNTERS) ? \
 			  NR_VM_EVENT_ITEMS : 0))
 
@@ -1827,7 +1827,7 @@ static void *vmstat_start(struct seq_file *m, loff_t *pos)
 
 	global_dirty_limits(v + NR_DIRTY_BG_THRESHOLD,
 			    v + NR_DIRTY_THRESHOLD);
-	v += NR_VM_WRITEBACK_STAT_ITEMS;
+	v += NR_VM_STAT_ITEMS;
 
 #ifdef CONFIG_VM_EVENT_COUNTERS
 	all_vm_events(v);
-- 
2.46.0.76.ge559c4bf1a-goog

[PATCH v4 3/3] mm: don't account memmap per-node

[Pasha Tatashin]

Fix invalid access to pgdat during hot-remove operation:
ndctl users reported a GPF when trying to destroy a namespace:
$ ndctl destroy-namespace all -r all -f
 Segmentation fault
 dmesg:
 Oops: general protection fault, probably for
 non-canonical address 0xdffffc0000005650: 0000 [#1] PREEMPT SMP KASAN
 PTI
 KASAN: probably user-memory-access in range
 [0x000000000002b280-0x000000000002b287]
 CPU: 26 UID: 0 PID: 1868 Comm: ndctl Not tainted 6.11.0-rc1 #1
 Hardware name: Dell Inc. PowerEdge R640/08HT8T, BIOS
 2.20.1 09/13/2023
 RIP: 0010:mod_node_page_state+0x2a/0x110

cxl-test users report a GPF when trying to unload the test module:
$ modrpobe -r cxl-test
 dmesg
 BUG: unable to handle page fault for address: 0000000000004200
 #PF: supervisor read access in kernel mode
 #PF: error_code(0x0000) - not-present page
 PGD 0 P4D 0
 Oops: Oops: 0000 [#1] PREEMPT SMP PTI
 CPU: 0 UID: 0 PID: 1076 Comm: modprobe Tainted: G O N 6.11.0-rc1 #197
 Tainted: [O]=OOT_MODULE, [N]=TEST
 Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 0.0.0 02/06/15
 RIP: 0010:mod_node_page_state+0x6/0x90

Currently, when memory is hot-plugged or hot-removed the accounting is
done based on the assumption that memmap is allocated from the same node
as the hot-plugged/hot-removed memory, which is not always the case.

In addition, there are challenges with keeping the node id of the memory
that is being remove to the time when memmap accounting is actually
performed: since this is done after remove_pfn_range_from_zone(), and
also after remove_memory_block_devices(). Meaning that we cannot use
pgdat nor walking though memblocks to get the nid.

Given all of that, account the memmap overhead system wide instead.

For this we are going to be using global atomic counters, but given that
memmap size is rarely modified, and normally is only modified either
during early boot when there is only one CPU, or under a hotplug global
mutex lock, therefore there is no need for per-cpu optimizations.

Also, while we are here rename nr_memmap to nr_memmap_pages, and
nr_memmap_boot to nr_memmap_boot_pages to be self explanatory that the
units are in page count.

Reported-by: Yi Zhang <yi.zhang@redhat.com>
Closes: https://lore.kernel.org/linux-cxl/CAHj4cs9Ax1=CoJkgBGP_+sNu6-6=6v=_L-ZBZY0bVLD3wUWZQg@mail.gmail.com
Reported-by: Alison Schofield <alison.schofield@intel.com>
Closes: https://lore.kernel.org/linux-mm/Zq0tPd2h6alFz8XF@aschofie-mobl2/#t

Fixes: 15995a352474 ("mm: report per-page metadata information")
Signed-off-by: Pasha Tatashin <pasha.tatashin@soleen.com>
Tested-by: Dan Williams <dan.j.williams@intel.com>
---
 include/linux/mmzone.h |  2 --
 include/linux/vmstat.h |  7 ++++---
 mm/hugetlb_vmemmap.c   |  8 ++++----
 mm/mm_init.c           |  3 +--
 mm/page_alloc.c        |  1 -
 mm/page_ext.c          | 18 ++++-------------
 mm/sparse-vmemmap.c    | 11 ++++-------
 mm/sparse.c            |  5 ++---
 mm/vmstat.c            | 45 ++++++++++++++++++++----------------------
 9 files changed, 40 insertions(+), 60 deletions(-)

diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
index 41458892bc8a..1dc6248feb83 100644
--- a/include/linux/mmzone.h
+++ b/include/linux/mmzone.h
@@ -220,8 +220,6 @@ enum node_stat_item {
 	PGDEMOTE_KSWAPD,
 	PGDEMOTE_DIRECT,
 	PGDEMOTE_KHUGEPAGED,
-	NR_MEMMAP, /* page metadata allocated through buddy allocator */
-	NR_MEMMAP_BOOT, /* page metadata allocated through boot allocator */
 	NR_VM_NODE_STAT_ITEMS
 };
 
diff --git a/include/linux/vmstat.h b/include/linux/vmstat.h
index 9ab4fa5e09b5..596c050ed492 100644
--- a/include/linux/vmstat.h
+++ b/include/linux/vmstat.h
@@ -38,6 +38,8 @@ struct reclaim_stat {
 enum vm_stat_item {
 	NR_DIRTY_THRESHOLD,
 	NR_DIRTY_BG_THRESHOLD,
+	NR_MEMMAP,	/* page metadata allocated through buddy allocator */
+	NR_MEMMAP_BOOT,	/* page metadata allocated through boot allocator */
 	NR_VM_STAT_ITEMS,
 };
 
@@ -618,7 +620,6 @@ static inline void lruvec_stat_sub_folio(struct folio *folio,
 	lruvec_stat_mod_folio(folio, idx, -folio_nr_pages(folio));
 }
 
-void __meminit mod_node_early_perpage_metadata(int nid, long delta);
-void __meminit store_early_perpage_metadata(void);
-
+void mod_memmap_boot(long delta);
+void mod_memmap(long delta);
 #endif /* _LINUX_VMSTAT_H */
diff --git a/mm/hugetlb_vmemmap.c b/mm/hugetlb_vmemmap.c
index 4f51e0596197..60a5faa1f341 100644
--- a/mm/hugetlb_vmemmap.c
+++ b/mm/hugetlb_vmemmap.c
@@ -185,11 +185,11 @@ static int vmemmap_remap_range(unsigned long start, unsigned long end,
 static inline void free_vmemmap_page(struct page *page)
 {
 	if (PageReserved(page)) {
+		mod_memmap_boot(-1);
 		free_bootmem_page(page);
-		mod_node_page_state(page_pgdat(page), NR_MEMMAP_BOOT, -1);
 	} else {
+		mod_memmap(-1);
 		__free_page(page);
-		mod_node_page_state(page_pgdat(page), NR_MEMMAP, -1);
 	}
 }
 
@@ -341,7 +341,7 @@ static int vmemmap_remap_free(unsigned long start, unsigned long end,
 		copy_page(page_to_virt(walk.reuse_page),
 			  (void *)walk.reuse_addr);
 		list_add(&walk.reuse_page->lru, vmemmap_pages);
-		mod_node_page_state(NODE_DATA(nid), NR_MEMMAP, 1);
+		mod_memmap(1);
 	}
 
 	/*
@@ -396,7 +396,7 @@ static int alloc_vmemmap_page_list(unsigned long start, unsigned long end,
 			goto out;
 		list_add(&page->lru, list);
 	}
-	mod_node_page_state(NODE_DATA(nid), NR_MEMMAP, nr_pages);
+	mod_memmap(nr_pages);
 
 	return 0;
 out:
diff --git a/mm/mm_init.c b/mm/mm_init.c
index 75c3bd42799b..29677274e74e 100644
--- a/mm/mm_init.c
+++ b/mm/mm_init.c
@@ -1623,8 +1623,7 @@ static void __init alloc_node_mem_map(struct pglist_data *pgdat)
 		panic("Failed to allocate %ld bytes for node %d memory map\n",
 		      size, pgdat->node_id);
 	pgdat->node_mem_map = map + offset;
-	mod_node_early_perpage_metadata(pgdat->node_id,
-					DIV_ROUND_UP(size, PAGE_SIZE));
+	mod_memmap_boot(DIV_ROUND_UP(size, PAGE_SIZE));
 	pr_debug("%s: node %d, pgdat %08lx, node_mem_map %08lx\n",
 		 __func__, pgdat->node_id, (unsigned long)pgdat,
 		 (unsigned long)pgdat->node_mem_map);
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 28f80daf5c04..875d76e8684a 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -5755,7 +5755,6 @@ void __init setup_per_cpu_pageset(void)
 	for_each_online_pgdat(pgdat)
 		pgdat->per_cpu_nodestats =
 			alloc_percpu(struct per_cpu_nodestat);
-	store_early_perpage_metadata();
 }
 
 __meminit void zone_pcp_init(struct zone *zone)
diff --git a/mm/page_ext.c b/mm/page_ext.c
index c191e490c401..c9419f6abfa0 100644
--- a/mm/page_ext.c
+++ b/mm/page_ext.c
@@ -214,8 +214,7 @@ static int __init alloc_node_page_ext(int nid)
 		return -ENOMEM;
 	NODE_DATA(nid)->node_page_ext = base;
 	total_usage += table_size;
-	mod_node_page_state(NODE_DATA(nid), NR_MEMMAP_BOOT,
-			    DIV_ROUND_UP(table_size, PAGE_SIZE));
+	mod_memmap_boot(DIV_ROUND_UP(table_size, PAGE_SIZE));
 	return 0;
 }
 
@@ -275,10 +274,8 @@ static void *__meminit alloc_page_ext(size_t size, int nid)
 	else
 		addr = vzalloc_node(size, nid);
 
-	if (addr) {
-		mod_node_page_state(NODE_DATA(nid), NR_MEMMAP,
-				    DIV_ROUND_UP(size, PAGE_SIZE));
-	}
+	if (addr)
+		mod_memmap(DIV_ROUND_UP(size, PAGE_SIZE));
 
 	return addr;
 }
@@ -323,25 +320,18 @@ static void free_page_ext(void *addr)
 {
 	size_t table_size;
 	struct page *page;
-	struct pglist_data *pgdat;
 
 	table_size = page_ext_size * PAGES_PER_SECTION;
+	mod_memmap(-1L * (DIV_ROUND_UP(table_size, PAGE_SIZE)));
 
 	if (is_vmalloc_addr(addr)) {
-		page = vmalloc_to_page(addr);
-		pgdat = page_pgdat(page);
 		vfree(addr);
 	} else {
 		page = virt_to_page(addr);
-		pgdat = page_pgdat(page);
 		BUG_ON(PageReserved(page));
 		kmemleak_free(addr);
 		free_pages_exact(addr, table_size);
 	}
-
-	mod_node_page_state(pgdat, NR_MEMMAP,
-			    -1L * (DIV_ROUND_UP(table_size, PAGE_SIZE)));
-
 }
 
 static void __free_page_ext(unsigned long pfn)
diff --git a/mm/sparse-vmemmap.c b/mm/sparse-vmemmap.c
index 1dda6c53370b..307f6fe83598 100644
--- a/mm/sparse-vmemmap.c
+++ b/mm/sparse-vmemmap.c
@@ -469,13 +469,10 @@ struct page * __meminit __populate_section_memmap(unsigned long pfn,
 	if (r < 0)
 		return NULL;
 
-	if (system_state == SYSTEM_BOOTING) {
-		mod_node_early_perpage_metadata(nid, DIV_ROUND_UP(end - start,
-								  PAGE_SIZE));
-	} else {
-		mod_node_page_state(NODE_DATA(nid), NR_MEMMAP,
-				    DIV_ROUND_UP(end - start, PAGE_SIZE));
-	}
+	if (system_state == SYSTEM_BOOTING)
+		mod_memmap_boot(DIV_ROUND_UP(end - start, PAGE_SIZE));
+	else
+		mod_memmap(DIV_ROUND_UP(end - start, PAGE_SIZE));
 
 	return pfn_to_page(pfn);
 }
diff --git a/mm/sparse.c b/mm/sparse.c
index e4b830091d13..9cc80ba1f7c1 100644
--- a/mm/sparse.c
+++ b/mm/sparse.c
@@ -463,7 +463,7 @@ static void __init sparse_buffer_init(unsigned long size, int nid)
 	sparsemap_buf = memmap_alloc(size, section_map_size(), addr, nid, true);
 	sparsemap_buf_end = sparsemap_buf + size;
 #ifndef CONFIG_SPARSEMEM_VMEMMAP
-	mod_node_early_perpage_metadata(nid, DIV_ROUND_UP(size, PAGE_SIZE));
+	mod_memmap_boot(DIV_ROUND_UP(size, PAGE_SIZE));
 #endif
 }
 
@@ -643,8 +643,7 @@ static void depopulate_section_memmap(unsigned long pfn, unsigned long nr_pages,
 	unsigned long start = (unsigned long) pfn_to_page(pfn);
 	unsigned long end = start + nr_pages * sizeof(struct page);
 
-	mod_node_page_state(page_pgdat(pfn_to_page(pfn)), NR_MEMMAP,
-			    -1L * (DIV_ROUND_UP(end - start, PAGE_SIZE)));
+	mod_memmap(-1L * (DIV_ROUND_UP(end - start, PAGE_SIZE)));
 	vmemmap_free(start, end, altmap);
 }
 static void free_map_bootmem(struct page *memmap)
diff --git a/mm/vmstat.c b/mm/vmstat.c
index 6f8aa4766f16..ad82c1bf0e63 100644
--- a/mm/vmstat.c
+++ b/mm/vmstat.c
@@ -1033,6 +1033,23 @@ unsigned long node_page_state(struct pglist_data *pgdat,
 }
 #endif
 
+/*
+ * Count number of pages "struct page" and "struct page_ext" consume.
+ * nr_memmap_boot: # of pages allocated by boot allocator & not part of MemTotal
+ * nr_memmap: # of pages that were allocated by buddy allocator
+ */
+static atomic_long_t nr_memmap_boot, nr_memmap;
+
+void mod_memmap_boot(long delta)
+{
+	atomic_long_add(delta, &nr_memmap_boot);
+}
+
+void mod_memmap(long delta)
+{
+	atomic_long_add(delta, &nr_memmap);
+}
+
 #ifdef CONFIG_COMPACTION
 
 struct contig_page_info {
@@ -1255,11 +1272,11 @@ const char * const vmstat_text[] = {
 	"pgdemote_kswapd",
 	"pgdemote_direct",
 	"pgdemote_khugepaged",
-	"nr_memmap",
-	"nr_memmap_boot",
 	/* system-wide enum vm_stat_item counters */
 	"nr_dirty_threshold",
 	"nr_dirty_background_threshold",
+	"nr_memmap_pages",
+	"nr_memmap_boot_pages",
 
 #if defined(CONFIG_VM_EVENT_COUNTERS) || defined(CONFIG_MEMCG)
 	/* enum vm_event_item counters */
@@ -1827,6 +1844,8 @@ static void *vmstat_start(struct seq_file *m, loff_t *pos)
 
 	global_dirty_limits(v + NR_DIRTY_BG_THRESHOLD,
 			    v + NR_DIRTY_THRESHOLD);
+	v[NR_MEMMAP_BOOT] = atomic_long_read(&nr_memmap_boot);
+	v[NR_MEMMAP] = atomic_long_read(&nr_memmap);
 	v += NR_VM_STAT_ITEMS;
 
 #ifdef CONFIG_VM_EVENT_COUNTERS
@@ -2285,25 +2304,3 @@ static int __init extfrag_debug_init(void)
 module_init(extfrag_debug_init);
 
 #endif
-
-/*
- * Page metadata size (struct page and page_ext) in pages
- */
-static unsigned long early_perpage_metadata[MAX_NUMNODES] __meminitdata;
-
-void __meminit mod_node_early_perpage_metadata(int nid, long delta)
-{
-	early_perpage_metadata[nid] += delta;
-}
-
-void __meminit store_early_perpage_metadata(void)
-{
-	int nid;
-	struct pglist_data *pgdat;
-
-	for_each_online_pgdat(pgdat) {
-		nid = pgdat->node_id;
-		mod_node_page_state(NODE_DATA(nid), NR_MEMMAP_BOOT,
-				    early_perpage_metadata[nid]);
-	}
-}
-- 
2.46.0.76.ge559c4bf1a-goog

Re: [PATCH v4 0/3] Fixes for memmap accounting

[Alison Schofield]

On Thu, Aug 08, 2024 at 09:34:33PM +0000, Pasha Tatashin wrote:
> Memmap accounting provides us with observability of how much memory is
> used for per-page metadata: i.e. "struct page"'s and "struct page_ext".
> It also provides with information of how much was allocated using
> boot allocator (i.e. not part of MemTotal), and how much was allocated
> using buddy allocated (i.e. part of MemTotal).
> 
> This small series fixes a few problems that were discovered with the
> original patch.

Thanks Pasha!
These fixups unblock the unit tests for dax, nvdimm, cxl.

Tested-by: Alison Schofield <alison.schofield@intel.com>

snip
> 

Re: [PATCH v4 2/3] mm: add system wide stats items category

[David Hildenbrand]

On 08.08.24 23:34, Pasha Tatashin wrote:
> /proc/vmstat contains events and stats, events can only grow, but stats
> can grow and shrink.
> 
> vmstat has the following:
> -------------------------
> NR_VM_ZONE_STAT_ITEMS:	per-zone stats
> NR_VM_NUMA_EVENT_ITEMS:	per-numa events
> NR_VM_NODE_STAT_ITEMS:	per-numa stats
> NR_VM_WRITEBACK_STAT_ITEMS:	system-wide background-writeback and
> 				dirty-throttling tresholds.
> NR_VM_EVENT_ITEMS:	system-wide events
> -------------------------
> 
> Rename NR_VM_WRITEBACK_STAT_ITEMS to NR_VM_STAT_ITEMS, to track the
> system-wide stats, we are going to add per-page metadata stats to this
> category in the next patch.
> 
> Also delete unused writeback_stat_name() function.
> 
> Suggested-by: Yosry Ahmed <yosryahmed@google.com>
> Signed-off-by: Pasha Tatashin <pasha.tatashin@soleen.com>
> ---

Acked-by: David Hildenbrand <david@redhat.com>

-- 
Cheers,

David / dhildenb

Re: [PATCH v4 3/3] mm: don't account memmap per-node

[David Hildenbrand]

On 08.08.24 23:34, Pasha Tatashin wrote:
> Fix invalid access to pgdat during hot-remove operation:
> ndctl users reported a GPF when trying to destroy a namespace:
> $ ndctl destroy-namespace all -r all -f
>   Segmentation fault
>   dmesg:
>   Oops: general protection fault, probably for
>   non-canonical address 0xdffffc0000005650: 0000 [#1] PREEMPT SMP KASAN
>   PTI
>   KASAN: probably user-memory-access in range
>   [0x000000000002b280-0x000000000002b287]
>   CPU: 26 UID: 0 PID: 1868 Comm: ndctl Not tainted 6.11.0-rc1 #1
>   Hardware name: Dell Inc. PowerEdge R640/08HT8T, BIOS
>   2.20.1 09/13/2023
>   RIP: 0010:mod_node_page_state+0x2a/0x110
> 
> cxl-test users report a GPF when trying to unload the test module:
> $ modrpobe -r cxl-test
>   dmesg
>   BUG: unable to handle page fault for address: 0000000000004200
>   #PF: supervisor read access in kernel mode
>   #PF: error_code(0x0000) - not-present page
>   PGD 0 P4D 0
>   Oops: Oops: 0000 [#1] PREEMPT SMP PTI
>   CPU: 0 UID: 0 PID: 1076 Comm: modprobe Tainted: G O N 6.11.0-rc1 #197
>   Tainted: [O]=OOT_MODULE, [N]=TEST
>   Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 0.0.0 02/06/15
>   RIP: 0010:mod_node_page_state+0x6/0x90
> 
> Currently, when memory is hot-plugged or hot-removed the accounting is
> done based on the assumption that memmap is allocated from the same node
> as the hot-plugged/hot-removed memory, which is not always the case.
> 
> In addition, there are challenges with keeping the node id of the memory
> that is being remove to the time when memmap accounting is actually
> performed: since this is done after remove_pfn_range_from_zone(), and
> also after remove_memory_block_devices(). Meaning that we cannot use
> pgdat nor walking though memblocks to get the nid.
> 
> Given all of that, account the memmap overhead system wide instead.
> 
> For this we are going to be using global atomic counters, but given that
> memmap size is rarely modified, and normally is only modified either
> during early boot when there is only one CPU, or under a hotplug global
> mutex lock, therefore there is no need for per-cpu optimizations.
> 
> Also, while we are here rename nr_memmap to nr_memmap_pages, and
> nr_memmap_boot to nr_memmap_boot_pages to be self explanatory that the
> units are in page count.
> 
> Reported-by: Yi Zhang <yi.zhang@redhat.com>
> Closes: https://lore.kernel.org/linux-cxl/CAHj4cs9Ax1=CoJkgBGP_+sNu6-6=6v=_L-ZBZY0bVLD3wUWZQg@mail.gmail.com
> Reported-by: Alison Schofield <alison.schofield@intel.com>
> Closes: https://lore.kernel.org/linux-mm/Zq0tPd2h6alFz8XF@aschofie-mobl2/#t
> 
> Fixes: 15995a352474 ("mm: report per-page metadata information")
> Signed-off-by: Pasha Tatashin <pasha.tatashin@soleen.com>
> Tested-by: Dan Williams <dan.j.williams@intel.com>
> ---

[...]

In general

Acked-by: David Hildenbrand <david@redhat.com>

Two nits below:


>   static void free_map_bootmem(struct page *memmap)
> diff --git a/mm/vmstat.c b/mm/vmstat.c
> index 6f8aa4766f16..ad82c1bf0e63 100644
> --- a/mm/vmstat.c
> +++ b/mm/vmstat.c
> @@ -1033,6 +1033,23 @@ unsigned long node_page_state(struct pglist_data *pgdat,
>   }
>   #endif
>   
> +/*
> + * Count number of pages "struct page" and "struct page_ext" consume.
> + * nr_memmap_boot: # of pages allocated by boot allocator & not part of MemTotal
> + * nr_memmap: # of pages that were allocated by buddy allocator
> + */
> +static atomic_long_t nr_memmap_boot, nr_memmap;

I *think* the clean and portable way to do it is use ATOMIC_INIT(0) for 
both. [even though what you have likely works on all archs]

> +
> +void mod_memmap_boot(long delta)
> +{
> +	atomic_long_add(delta, &nr_memmap_boot);
> +}
> +
> +void mod_memmap(long delta)
> +{
> +	atomic_long_add(delta, &nr_memmap);
> +}
> +

Nit picking: (up to you)

I'd do it similar to totalram_pages_add():

memmap_pages_add()
memmap_boot_pages_add()

And call the variables something like

static atomic_long_t memmap_pages_boot, memmap_pages;


-- 
Cheers,

David / dhildenb

Re: [PATCH v4 3/3] mm: don't account memmap per-node

[Pasha Tatashin]

On Fri, Aug 9, 2024 at 3:31 AM David Hildenbrand <david@redhat.com> wrote:
>
> On 08.08.24 23:34, Pasha Tatashin wrote:
> > Fix invalid access to pgdat during hot-remove operation:
> > ndctl users reported a GPF when trying to destroy a namespace:
> > $ ndctl destroy-namespace all -r all -f
> >   Segmentation fault
> >   dmesg:
> >   Oops: general protection fault, probably for
> >   non-canonical address 0xdffffc0000005650: 0000 [#1] PREEMPT SMP KASAN
> >   PTI
> >   KASAN: probably user-memory-access in range
> >   [0x000000000002b280-0x000000000002b287]
> >   CPU: 26 UID: 0 PID: 1868 Comm: ndctl Not tainted 6.11.0-rc1 #1
> >   Hardware name: Dell Inc. PowerEdge R640/08HT8T, BIOS
> >   2.20.1 09/13/2023
> >   RIP: 0010:mod_node_page_state+0x2a/0x110
> >
> > cxl-test users report a GPF when trying to unload the test module:
> > $ modrpobe -r cxl-test
> >   dmesg
> >   BUG: unable to handle page fault for address: 0000000000004200
> >   #PF: supervisor read access in kernel mode
> >   #PF: error_code(0x0000) - not-present page
> >   PGD 0 P4D 0
> >   Oops: Oops: 0000 [#1] PREEMPT SMP PTI
> >   CPU: 0 UID: 0 PID: 1076 Comm: modprobe Tainted: G O N 6.11.0-rc1 #197
> >   Tainted: [O]=OOT_MODULE, [N]=TEST
> >   Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 0.0.0 02/06/15
> >   RIP: 0010:mod_node_page_state+0x6/0x90
> >
> > Currently, when memory is hot-plugged or hot-removed the accounting is
> > done based on the assumption that memmap is allocated from the same node
> > as the hot-plugged/hot-removed memory, which is not always the case.
> >
> > In addition, there are challenges with keeping the node id of the memory
> > that is being remove to the time when memmap accounting is actually
> > performed: since this is done after remove_pfn_range_from_zone(), and
> > also after remove_memory_block_devices(). Meaning that we cannot use
> > pgdat nor walking though memblocks to get the nid.
> >
> > Given all of that, account the memmap overhead system wide instead.
> >
> > For this we are going to be using global atomic counters, but given that
> > memmap size is rarely modified, and normally is only modified either
> > during early boot when there is only one CPU, or under a hotplug global
> > mutex lock, therefore there is no need for per-cpu optimizations.
> >
> > Also, while we are here rename nr_memmap to nr_memmap_pages, and
> > nr_memmap_boot to nr_memmap_boot_pages to be self explanatory that the
> > units are in page count.
> >
> > Reported-by: Yi Zhang <yi.zhang@redhat.com>
> > Closes: https://lore.kernel.org/linux-cxl/CAHj4cs9Ax1=CoJkgBGP_+sNu6-6=6v=_L-ZBZY0bVLD3wUWZQg@mail.gmail.com
> > Reported-by: Alison Schofield <alison.schofield@intel.com>
> > Closes: https://lore.kernel.org/linux-mm/Zq0tPd2h6alFz8XF@aschofie-mobl2/#t
> >
> > Fixes: 15995a352474 ("mm: report per-page metadata information")
> > Signed-off-by: Pasha Tatashin <pasha.tatashin@soleen.com>
> > Tested-by: Dan Williams <dan.j.williams@intel.com>
> > ---
>
> [...]
>
> In general
>
> Acked-by: David Hildenbrand <david@redhat.com>
>
> Two nits below:
>
>
> >   static void free_map_bootmem(struct page *memmap)
> > diff --git a/mm/vmstat.c b/mm/vmstat.c
> > index 6f8aa4766f16..ad82c1bf0e63 100644
> > --- a/mm/vmstat.c
> > +++ b/mm/vmstat.c
> > @@ -1033,6 +1033,23 @@ unsigned long node_page_state(struct pglist_data *pgdat,
> >   }
> >   #endif
> >
> > +/*
> > + * Count number of pages "struct page" and "struct page_ext" consume.
> > + * nr_memmap_boot: # of pages allocated by boot allocator & not part of MemTotal
> > + * nr_memmap: # of pages that were allocated by buddy allocator
> > + */
> > +static atomic_long_t nr_memmap_boot, nr_memmap;
>
> I *think* the clean and portable way to do it is use ATOMIC_INIT(0) for
> both. [even though what you have likely works on all archs]

Yeah, it is not necessary, but I will add ATOMIC_LONG_INIT(0),

>
> > +
> > +void mod_memmap_boot(long delta)
> > +{
> > +     atomic_long_add(delta, &nr_memmap_boot);
> > +}
> > +
> > +void mod_memmap(long delta)
> > +{
> > +     atomic_long_add(delta, &nr_memmap);
> > +}
> > +
>
> Nit picking: (up to you)
>
> I'd do it similar to totalram_pages_add():
>
> memmap_pages_add()
> memmap_boot_pages_add()
>
> And call the variables something like
>
> static atomic_long_t memmap_pages_boot, memmap_pages;

Sure, I will rename them.

Pasha