[PATCH v1 04/11] mm/memremap: add ZONE_DEVICE support for compound pages

Joao Martins
2021-03-25T23:10:38Z

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 these pages are initialised, most 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@oracle.com>
---
include/linux/memremap.h | 13 +++++++++++++
mm/memremap.c | 8 ++++++--
mm/page_alloc.c | 24 +++++++++++++++++++++++-
3 files changed, 42 insertions(+), 3 deletions(-)

diff --git a/include/linux/memremap.h b/include/linux/memremap.h
index b46f63dcaed3..bb28d82dda5e 100644
--- a/include/linux/memremap.h
+++ b/include/linux/memremap.h
@@ -114,6 +114,7 @@ struct dev_pagemap {
struct completion done;
enum memory_type type;
unsigned int flags;
+ unsigned long align;
const struct dev_pagemap_ops *ops;
void *owner;
int nr_range;
@@ -130,6 +131,18 @@ static inline struct vmem_altmap *pgmap_altmap(struct dev_pagemap *pgmap)
return NULL;
}

+static inline unsigned long pgmap_align(struct dev_pagemap *pgmap)
+{
+ if (!pgmap || !pgmap->align)
+ return PAGE_SIZE;
+ return pgmap->align;
+}
+
+static inline unsigned long pgmap_pfn_align(struct dev_pagemap *pgmap)
+{
+ return PHYS_PFN(pgmap_align(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..d160853670c4 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_align(pgmap) > PAGE_SIZE)
+ percpu_ref_get_many(pgmap->ref, (pfn_end(pgmap, range_id)
+ - pfn_first(pgmap, range_id)) / pgmap_pfn_align(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 58974067bbd4..3a77f9e43f3a 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -6285,6 +6285,8 @@ 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 pfn_align = pgmap_pfn_align(pgmap);
+ unsigned int order_align = order_base_2(pfn_align);
unsigned long zone_idx = zone_idx(zone);
unsigned long start = jiffies;
int nid = pgdat->node_id;
@@ -6302,10 +6304,30 @@ 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 += pfn_align) {
struct page *page = pfn_to_page(pfn);
+ unsigned long i;

__init_zone_device_page(page, pfn, zone_idx, nid, pgmap);
+
+ if (pfn_align == 1)
+ continue;
+
+ __SetPageHead(page);
+
+ for (i = 1; i < pfn_align; 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);
+ }
}

pr_info("%s initialised %lu pages in %ums\n", __func__,
--
2.17.1