[PATCH v8 01/12] mm/sparsemem: Introduce struct mem_section_usage

From: Dan Williams
Date: Mon May 06 2019 - 19:54:09 EST

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Towards enabling memory hotplug to track partial population of a
section, introduce 'struct mem_section_usage'.

A pointer to a 'struct mem_section_usage' instance replaces the existing
pointer to a 'pageblock_flags' bitmap. Effectively it adds one more
'unsigned long' beyond the 'pageblock_flags' (usemap) allocation to
house a new 'subsection_map' bitmap. The new bitmap enables the memory
hot{plug,remove} implementation to act on incremental sub-divisions of a
section.

The default SUBSECTION_SHIFT is chosen to keep the 'subsection_map' no
larger than a single 'unsigned long' on the major architectures.
Alternatively an architecture can define ARCH_SUBSECTION_SHIFT to
override the default PMD_SHIFT. Note that PowerPC needs to use
ARCH_SUBSECTION_SHIFT to workaround PMD_SHIFT being a non-constant
expression on PowerPC.

The primary motivation for this functionality is to support platforms
that mix "System RAM" and "Persistent Memory" within a single section,
or multiple PMEM ranges with different mapping lifetimes within a single
section. The section restriction for hotplug has caused an ongoing saga
of hacks and bugs for devm_memremap_pages() users.

Beyond the fixups to teach existing paths how to retrieve the 'usemap'
from a section, and updates to usemap allocation path, there are no
expected behavior changes.

Cc: Michal Hocko <mhocko@xxxxxxxx>
Cc: Vlastimil Babka <vbabka@xxxxxxx>
Cc: Logan Gunthorpe <logang@xxxxxxxxxxxx>
Cc: Oscar Salvador <osalvador@xxxxxxx>
Cc: Pavel Tatashin <pasha.tatashin@xxxxxxxxxx>
Cc: Benjamin Herrenschmidt <benh@xxxxxxxxxxxxxxxxxxx>
Cc: Paul Mackerras <paulus@xxxxxxxxx>
Cc: Michael Ellerman <mpe@xxxxxxxxxxxxxx>
Signed-off-by: Dan Williams <dan.j.williams@xxxxxxxxx>
---
arch/powerpc/include/asm/sparsemem.h | 3 +
include/linux/mmzone.h | 48 +++++++++++++++++++-
mm/memory_hotplug.c | 18 ++++----
mm/page_alloc.c | 2 -
mm/sparse.c | 81 +++++++++++++++++-----------------
5 files changed, 99 insertions(+), 53 deletions(-)

diff --git a/arch/powerpc/include/asm/sparsemem.h b/arch/powerpc/include/asm/sparsemem.h
index 3192d454a733..1aa3c9303bf8 100644
--- a/arch/powerpc/include/asm/sparsemem.h
+++ b/arch/powerpc/include/asm/sparsemem.h
@@ -10,6 +10,9 @@
*/
#define SECTION_SIZE_BITS 24

+/* Reflect the largest possible PMD-size as the subsection-size constant */
+#define ARCH_SUBSECTION_SHIFT 24
+
#endif /* CONFIG_SPARSEMEM */

#ifdef CONFIG_MEMORY_HOTPLUG
diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
index 70394cabaf4e..ef8d878079f9 100644
--- a/include/linux/mmzone.h
+++ b/include/linux/mmzone.h
@@ -1160,6 +1160,44 @@ static inline unsigned long section_nr_to_pfn(unsigned long sec)
#define SECTION_ALIGN_UP(pfn) (((pfn) + PAGES_PER_SECTION - 1) & PAGE_SECTION_MASK)
#define SECTION_ALIGN_DOWN(pfn) ((pfn) & PAGE_SECTION_MASK)

+/*
+ * SUBSECTION_SHIFT must be constant since it is used to declare
+ * subsection_map and related bitmaps without triggering the generation
+ * of variable-length arrays. The most natural size for a subsection is
+ * a PMD-page. For architectures that do not have a constant PMD-size
+ * ARCH_SUBSECTION_SHIFT can be set to a constant max size, or otherwise
+ * fallback to 2MB.
+ */
+#if defined(ARCH_SUBSECTION_SHIFT)
+#define SUBSECTION_SHIFT (ARCH_SUBSECTION_SHIFT)
+#elif defined(PMD_SHIFT)
+#define SUBSECTION_SHIFT (PMD_SHIFT)
+#else
+/*
+ * Memory hotplug enabled platforms avoid this default because they
+ * either define ARCH_SUBSECTION_SHIFT, or PMD_SHIFT is a constant, but
+ * this is kept as a backstop to allow compilation on
+ * !ARCH_ENABLE_MEMORY_HOTPLUG archs.
+ */
+#define SUBSECTION_SHIFT 21
+#endif
+
+#define PFN_SUBSECTION_SHIFT (SUBSECTION_SHIFT - PAGE_SHIFT)
+#define PAGES_PER_SUBSECTION (1UL << PFN_SUBSECTION_SHIFT)
+#define PAGE_SUBSECTION_MASK ((~(PAGES_PER_SUBSECTION-1)))
+
+#if SUBSECTION_SHIFT > SECTION_SIZE_BITS
+#error Subsection size exceeds section size
+#else
+#define SUBSECTIONS_PER_SECTION (1UL << (SECTION_SIZE_BITS - SUBSECTION_SHIFT))
+#endif
+
+struct mem_section_usage {
+ DECLARE_BITMAP(subsection_map, SUBSECTIONS_PER_SECTION);
+ /* See declaration of similar field in struct zone */
+ unsigned long pageblock_flags[0];
+};
+
struct page;
struct page_ext;
struct mem_section {
@@ -1177,8 +1215,7 @@ struct mem_section {
*/
unsigned long section_mem_map;

- /* See declaration of similar field in struct zone */
- unsigned long *pageblock_flags;
+ struct mem_section_usage *usage;
#ifdef CONFIG_PAGE_EXTENSION
/*
* If SPARSEMEM, pgdat doesn't have page_ext pointer. We use
@@ -1209,6 +1246,11 @@ extern struct mem_section **mem_section;
extern struct mem_section mem_section[NR_SECTION_ROOTS][SECTIONS_PER_ROOT];
#endif

+static inline unsigned long *section_to_usemap(struct mem_section *ms)
+{
+ return ms->usage->pageblock_flags;
+}
+
static inline struct mem_section *__nr_to_section(unsigned long nr)
{
#ifdef CONFIG_SPARSEMEM_EXTREME
@@ -1220,7 +1262,7 @@ static inline struct mem_section *__nr_to_section(unsigned long nr)
return &mem_section[SECTION_NR_TO_ROOT(nr)][nr & SECTION_ROOT_MASK];
}
extern int __section_nr(struct mem_section* ms);
-extern unsigned long usemap_size(void);
+extern size_t mem_section_usage_size(void);

/*
* We use the lower bits of the mem_map pointer to store
diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
index 328878b6799d..a76fc6a6e9fe 100644
--- a/mm/memory_hotplug.c
+++ b/mm/memory_hotplug.c
@@ -165,9 +165,10 @@ void put_page_bootmem(struct page *page)
#ifndef CONFIG_SPARSEMEM_VMEMMAP
static void register_page_bootmem_info_section(unsigned long start_pfn)
{
- unsigned long *usemap, mapsize, section_nr, i;
+ unsigned long mapsize, section_nr, i;
struct mem_section *ms;
struct page *page, *memmap;
+ struct mem_section_usage *usage;

section_nr = pfn_to_section_nr(start_pfn);
ms = __nr_to_section(section_nr);
@@ -187,10 +188,10 @@ static void register_page_bootmem_info_section(unsigned long start_pfn)
for (i = 0; i < mapsize; i++, page++)
get_page_bootmem(section_nr, page, SECTION_INFO);

- usemap = ms->pageblock_flags;
- page = virt_to_page(usemap);
+ usage = ms->usage;
+ page = virt_to_page(usage);

- mapsize = PAGE_ALIGN(usemap_size()) >> PAGE_SHIFT;
+ mapsize = PAGE_ALIGN(mem_section_usage_size()) >> PAGE_SHIFT;

for (i = 0; i < mapsize; i++, page++)
get_page_bootmem(section_nr, page, MIX_SECTION_INFO);
@@ -199,9 +200,10 @@ static void register_page_bootmem_info_section(unsigned long start_pfn)
#else /* CONFIG_SPARSEMEM_VMEMMAP */
static void register_page_bootmem_info_section(unsigned long start_pfn)
{
- unsigned long *usemap, mapsize, section_nr, i;
+ unsigned long mapsize, section_nr, i;
struct mem_section *ms;
struct page *page, *memmap;
+ struct mem_section_usage *usage;

section_nr = pfn_to_section_nr(start_pfn);
ms = __nr_to_section(section_nr);
@@ -210,10 +212,10 @@ static void register_page_bootmem_info_section(unsigned long start_pfn)

register_page_bootmem_memmap(section_nr, memmap, PAGES_PER_SECTION);

- usemap = ms->pageblock_flags;
- page = virt_to_page(usemap);
+ usage = ms->usage;
+ page = virt_to_page(usage);

- mapsize = PAGE_ALIGN(usemap_size()) >> PAGE_SHIFT;
+ mapsize = PAGE_ALIGN(mem_section_usage_size()) >> PAGE_SHIFT;

for (i = 0; i < mapsize; i++, page++)
get_page_bootmem(section_nr, page, MIX_SECTION_INFO);
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 1f99db76b1ff..61c2b54a5b61 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -403,7 +403,7 @@ static inline unsigned long *get_pageblock_bitmap(struct page *page,
unsigned long pfn)
{
#ifdef CONFIG_SPARSEMEM
- return __pfn_to_section(pfn)->pageblock_flags;
+ return section_to_usemap(__pfn_to_section(pfn));
#else
return page_zone(page)->pageblock_flags;
#endif /* CONFIG_SPARSEMEM */
diff --git a/mm/sparse.c b/mm/sparse.c
index fd13166949b5..f87de7ad32c8 100644
--- a/mm/sparse.c
+++ b/mm/sparse.c
@@ -288,33 +288,31 @@ struct page *sparse_decode_mem_map(unsigned long coded_mem_map, unsigned long pn

static void __meminit sparse_init_one_section(struct mem_section *ms,
unsigned long pnum, struct page *mem_map,
- unsigned long *pageblock_bitmap)
+ struct mem_section_usage *usage)
{
ms->section_mem_map &= ~SECTION_MAP_MASK;
ms->section_mem_map |= sparse_encode_mem_map(mem_map, pnum) |
SECTION_HAS_MEM_MAP;
- ms->pageblock_flags = pageblock_bitmap;
+ ms->usage = usage;
}

-unsigned long usemap_size(void)
+static unsigned long usemap_size(void)
{
return BITS_TO_LONGS(SECTION_BLOCKFLAGS_BITS) * sizeof(unsigned long);
}

-#ifdef CONFIG_MEMORY_HOTPLUG
-static unsigned long *__kmalloc_section_usemap(void)
+size_t mem_section_usage_size(void)
{
- return kmalloc(usemap_size(), GFP_KERNEL);
+ return sizeof(struct mem_section_usage) + usemap_size();
}
-#endif /* CONFIG_MEMORY_HOTPLUG */

#ifdef CONFIG_MEMORY_HOTREMOVE
-static unsigned long * __init
+static struct mem_section_usage * __init
sparse_early_usemaps_alloc_pgdat_section(struct pglist_data *pgdat,
unsigned long size)
{
+ struct mem_section_usage *usage;
unsigned long goal, limit;
- unsigned long *p;
int nid;
/*
* A page may contain usemaps for other sections preventing the
@@ -330,15 +328,16 @@ sparse_early_usemaps_alloc_pgdat_section(struct pglist_data *pgdat,
limit = goal + (1UL << PA_SECTION_SHIFT);
nid = early_pfn_to_nid(goal >> PAGE_SHIFT);
again:
- p = memblock_alloc_try_nid(size, SMP_CACHE_BYTES, goal, limit, nid);
- if (!p && limit) {
+ usage = memblock_alloc_try_nid(size, SMP_CACHE_BYTES, goal, limit, nid);
+ if (!usage && limit) {
limit = 0;
goto again;
}
- return p;
+ return usage;
}

-static void __init check_usemap_section_nr(int nid, unsigned long *usemap)
+static void __init check_usemap_section_nr(int nid,
+ struct mem_section_usage *usage)
{
unsigned long usemap_snr, pgdat_snr;
static unsigned long old_usemap_snr;
@@ -352,7 +351,7 @@ static void __init check_usemap_section_nr(int nid, unsigned long *usemap)
old_pgdat_snr = NR_MEM_SECTIONS;
}

- usemap_snr = pfn_to_section_nr(__pa(usemap) >> PAGE_SHIFT);
+ usemap_snr = pfn_to_section_nr(__pa(usage) >> PAGE_SHIFT);
pgdat_snr = pfn_to_section_nr(__pa(pgdat) >> PAGE_SHIFT);
if (usemap_snr == pgdat_snr)
return;
@@ -380,14 +379,15 @@ static void __init check_usemap_section_nr(int nid, unsigned long *usemap)
usemap_snr, pgdat_snr, nid);
}
#else
-static unsigned long * __init
+static struct mem_section_usage * __init
sparse_early_usemaps_alloc_pgdat_section(struct pglist_data *pgdat,
unsigned long size)
{
return memblock_alloc_node(size, SMP_CACHE_BYTES, pgdat->node_id);
}

-static void __init check_usemap_section_nr(int nid, unsigned long *usemap)
+static void __init check_usemap_section_nr(int nid,
+ struct mem_section_usage *usage)
{
}
#endif /* CONFIG_MEMORY_HOTREMOVE */
@@ -474,14 +474,13 @@ static void __init sparse_init_nid(int nid, unsigned long pnum_begin,
unsigned long pnum_end,
unsigned long map_count)
{
- unsigned long pnum, usemap_longs, *usemap;
+ struct mem_section_usage *usage;
+ unsigned long pnum;
struct page *map;

- usemap_longs = BITS_TO_LONGS(SECTION_BLOCKFLAGS_BITS);
- usemap = sparse_early_usemaps_alloc_pgdat_section(NODE_DATA(nid),
- usemap_size() *
- map_count);
- if (!usemap) {
+ usage = sparse_early_usemaps_alloc_pgdat_section(NODE_DATA(nid),
+ mem_section_usage_size() * map_count);
+ if (!usage) {
pr_err("%s: node[%d] usemap allocation failed", __func__, nid);
goto failed;
}
@@ -497,9 +496,9 @@ static void __init sparse_init_nid(int nid, unsigned long pnum_begin,
pnum_begin = pnum;
goto failed;
}
- check_usemap_section_nr(nid, usemap);
- sparse_init_one_section(__nr_to_section(pnum), pnum, map, usemap);
- usemap += usemap_longs;
+ check_usemap_section_nr(nid, usage);
+ sparse_init_one_section(__nr_to_section(pnum), pnum, map, usage);
+ usage = (void *) usage + mem_section_usage_size();
}
sparse_buffer_fini();
return;
@@ -701,9 +700,9 @@ int __meminit sparse_add_one_section(int nid, unsigned long start_pfn,
struct vmem_altmap *altmap)
{
unsigned long section_nr = pfn_to_section_nr(start_pfn);
+ struct mem_section_usage *usage;
struct mem_section *ms;
struct page *memmap;
- unsigned long *usemap;
int ret;

/*
@@ -717,8 +716,8 @@ int __meminit sparse_add_one_section(int nid, unsigned long start_pfn,
memmap = kmalloc_section_memmap(section_nr, nid, altmap);
if (!memmap)
return -ENOMEM;
- usemap = __kmalloc_section_usemap();
- if (!usemap) {
+ usage = kzalloc(mem_section_usage_size(), GFP_KERNEL);
+ if (!usage) {
__kfree_section_memmap(memmap, altmap);
return -ENOMEM;
}
@@ -736,11 +735,11 @@ int __meminit sparse_add_one_section(int nid, unsigned long start_pfn,
page_init_poison(memmap, sizeof(struct page) * PAGES_PER_SECTION);

section_mark_present(ms);
- sparse_init_one_section(ms, section_nr, memmap, usemap);
+ sparse_init_one_section(ms, section_nr, memmap, usage);

out:
if (ret < 0) {
- kfree(usemap);
+ kfree(usage);
__kfree_section_memmap(memmap, altmap);
}
return ret;
@@ -777,20 +776,20 @@ static inline void clear_hwpoisoned_pages(struct page *memmap, int nr_pages)
}
#endif

-static void free_section_usemap(struct page *memmap, unsigned long *usemap,
- struct vmem_altmap *altmap)
+static void free_section_usage(struct page *memmap,
+ struct mem_section_usage *usage, struct vmem_altmap *altmap)
{
- struct page *usemap_page;
+ struct page *usage_page;

- if (!usemap)
+ if (!usage)
return;

- usemap_page = virt_to_page(usemap);
+ usage_page = virt_to_page(usage);
/*
* Check to see if allocation came from hot-plug-add
*/
- if (PageSlab(usemap_page) || PageCompound(usemap_page)) {
- kfree(usemap);
+ if (PageSlab(usage_page) || PageCompound(usage_page)) {
+ kfree(usage);
if (memmap)
__kfree_section_memmap(memmap, altmap);
return;
@@ -809,19 +808,19 @@ void sparse_remove_one_section(struct zone *zone, struct mem_section *ms,
unsigned long map_offset, struct vmem_altmap *altmap)
{
struct page *memmap = NULL;
- unsigned long *usemap = NULL;
+ struct mem_section_usage *usage = NULL;

if (ms->section_mem_map) {
- usemap = ms->pageblock_flags;
+ usage = ms->usage;
memmap = sparse_decode_mem_map(ms->section_mem_map,
__section_nr(ms));
ms->section_mem_map = 0;
- ms->pageblock_flags = NULL;
+ ms->usage = NULL;
}

clear_hwpoisoned_pages(memmap + map_offset,
PAGES_PER_SECTION - map_offset);
- free_section_usemap(memmap, usemap, altmap);
+ free_section_usage(memmap, usage, altmap);
}
#endif /* CONFIG_MEMORY_HOTREMOVE */
#endif /* CONFIG_MEMORY_HOTPLUG */

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