Add a new align property for struct dev_pagemap which specifies that a
pagemap is composed of a set of compound pages of size @align, instead of
base pages. When a compound page geometry is requested, all but the first
page are initialised as tail pages instead of order-0 pages.
For certain ZONE_DEVICE users like device-dax which have a fixed page size,
this creates an opportunity to optimize GUP and GUP-fast walkers, treating
it the same way as THP or hugetlb pages.
Signed-off-by: Joao Martins <joao.m.martins@xxxxxxxxxx>
---
include/linux/memremap.h | 17 +++++++++++++++++
mm/memremap.c | 8 ++++++--
mm/page_alloc.c | 34 +++++++++++++++++++++++++++++++++-
3 files changed, 56 insertions(+), 3 deletions(-)
diff --git a/include/linux/memremap.h b/include/linux/memremap.h
index 119f130ef8f1..e5ab6d4525c1 100644
--- a/include/linux/memremap.h
+++ b/include/linux/memremap.h
@@ -99,6 +99,10 @@ struct dev_pagemap_ops {
* @done: completion for @internal_ref
* @type: memory type: see MEMORY_* in memory_hotplug.h
* @flags: PGMAP_* flags to specify defailed behavior
+ * @geometry: structural definition of how the vmemmap metadata is populated.
+ * A zero or PAGE_SIZE defaults to using base pages as the memmap metadata
+ * representation. A bigger value but also multiple of PAGE_SIZE will set
+ * up compound struct pages representative of the requested geometry size.
* @ops: method table
* @owner: an opaque pointer identifying the entity that manages this
* instance. Used by various helpers to make sure that no
@@ -114,6 +118,7 @@ struct dev_pagemap {
struct completion done;
enum memory_type type;
unsigned int flags;
+ unsigned long geometry;
const struct dev_pagemap_ops *ops;
void *owner;
int nr_range;
@@ -130,6 +135,18 @@ static inline struct vmem_altmap *pgmap_altmap(struct dev_pagemap *pgmap)
return NULL;
}
+static inline unsigned long pgmap_geometry(struct dev_pagemap *pgmap)
+{
+ if (!pgmap || !pgmap->geometry)
+ return PAGE_SIZE;
+ return pgmap->geometry;
+}
+
+static inline unsigned long pgmap_pfn_geometry(struct dev_pagemap *pgmap)
+{
+ return PHYS_PFN(pgmap_geometry(pgmap));
+}
+
#ifdef CONFIG_ZONE_DEVICE
bool pfn_zone_device_reserved(unsigned long pfn);
void *memremap_pages(struct dev_pagemap *pgmap, int nid);
diff --git a/mm/memremap.c b/mm/memremap.c
index 805d761740c4..ffcb924eb6a5 100644
--- a/mm/memremap.c
+++ b/mm/memremap.c
@@ -318,8 +318,12 @@ static int pagemap_range(struct dev_pagemap *pgmap, struct mhp_params *params,
memmap_init_zone_device(&NODE_DATA(nid)->node_zones[ZONE_DEVICE],
PHYS_PFN(range->start),
PHYS_PFN(range_len(range)), pgmap);
- percpu_ref_get_many(pgmap->ref, pfn_end(pgmap, range_id)
- - pfn_first(pgmap, range_id));
+ if (pgmap_geometry(pgmap) > PAGE_SIZE)
+ percpu_ref_get_many(pgmap->ref, (pfn_end(pgmap, range_id)
+ - pfn_first(pgmap, range_id)) / pgmap_pfn_geometry(pgmap));
+ else
+ percpu_ref_get_many(pgmap->ref, pfn_end(pgmap, range_id)
+ - pfn_first(pgmap, range_id));
return 0;
err_add_memory:
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 79f3b38afeca..188cb5f8c308 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -6597,6 +6597,31 @@ static void __ref __init_zone_device_page(struct page *page, unsigned long pfn,
}
}
+static void __ref memmap_init_compound(struct page *page, unsigned long pfn,
+ unsigned long zone_idx, int nid,
+ struct dev_pagemap *pgmap,
+ unsigned long nr_pages)
+{
+ unsigned int order_align = order_base_2(nr_pages);
+ unsigned long i;
+
+ __SetPageHead(page);
+
+ for (i = 1; i < nr_pages; i++) {
+ __init_zone_device_page(page + i, pfn + i, zone_idx,
+ nid, pgmap);
+ prep_compound_tail(page, i);
+
+ /*
+ * The first and second tail pages need to
+ * initialized first, hence the head page is
+ * prepared last.
+ */
+ if (i == 2)
+ prep_compound_head(page, order_align);
+ }
+}
+
void __ref memmap_init_zone_device(struct zone *zone,
unsigned long start_pfn,
unsigned long nr_pages,
@@ -6605,6 +6630,7 @@ void __ref memmap_init_zone_device(struct zone *zone,
unsigned long pfn, end_pfn = start_pfn + nr_pages;
struct pglist_data *pgdat = zone->zone_pgdat;
struct vmem_altmap *altmap = pgmap_altmap(pgmap);
+ unsigned int pfns_per_compound = pgmap_pfn_geometry(pgmap);
unsigned long zone_idx = zone_idx(zone);
unsigned long start = jiffies;
int nid = pgdat->node_id;
@@ -6622,10 +6648,16 @@ void __ref memmap_init_zone_device(struct zone *zone,
nr_pages = end_pfn - start_pfn;
}
- for (pfn = start_pfn; pfn < end_pfn; pfn++) {
+ for (pfn = start_pfn; pfn < end_pfn; pfn += pfns_per_compound) {
struct page *page = pfn_to_page(pfn);
__init_zone_device_page(page, pfn, zone_idx, nid, pgmap);
+
+ if (pfns_per_compound == 1)
+ continue;
+
+ memmap_init_compound(page, pfn, zone_idx, nid, pgmap,
+ pfns_per_compound);
}
pr_info("%s initialised %lu pages in %ums\n", __func__,
--
2.17.1
