[v1 4/6] memblock: introduce MEMBLOCK_RSRV_NOINIT flag

[Usama Arif <usama.arif@bytedance.com>]

For reserved memory regions marked with this flag,
reserve_bootmem_region is not called during memmap_init_reserved_pages.
This can be used to avoid struct page initialization for
regions which won't need them, for e.g. hugepages with
HVO enabled.

Signed-off-by: Usama Arif <usama.arif@bytedance.com>
---
 include/linux/memblock.h |  7 +++++++
 mm/memblock.c            | 32 ++++++++++++++++++++++++++------
 2 files changed, 33 insertions(+), 6 deletions(-)

diff --git a/include/linux/memblock.h b/include/linux/memblock.h
index f71ff9f0ec81..7f9d06c08592 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_RSRV_NOINIT	= 0x10,	/* don't call reserve_bootmem_region for this region */
 };
 
 /**
@@ -125,6 +126,7 @@ 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_rsrv_mark_noinit(phys_addr_t base, phys_addr_t size);
 
 void memblock_free_all(void);
 void memblock_free(void *ptr, size_t size);
@@ -259,6 +261,11 @@ static inline bool memblock_is_nomap(struct memblock_region *m)
 	return m->flags & MEMBLOCK_NOMAP;
 }
 
+static inline bool memblock_is_noinit(struct memblock_region *m)
+{
+	return m->flags & MEMBLOCK_RSRV_NOINIT;
+}
+
 static inline bool memblock_is_driver_managed(struct memblock_region *m)
 {
 	return m->flags & MEMBLOCK_DRIVER_MANAGED;
diff --git a/mm/memblock.c b/mm/memblock.c
index 4fd431d16ef2..3a15708af3b6 100644
--- a/mm/memblock.c
+++ b/mm/memblock.c
@@ -997,6 +997,22 @@ int __init_memblock memblock_clear_nomap(phys_addr_t base, phys_addr_t size)
 	return memblock_setclr_flag(base, size, 0, MEMBLOCK_NOMAP, 0);
 }
 
+/**
+ * memblock_rsrv_mark_noinit - Mark a reserved memory region with flag MEMBLOCK_RSRV_NOINIT.
+ * @base: the base phys addr of the region
+ * @size: the size of the region
+ *
+ * For memory regions marked with %MEMBLOCK_RSRV_NOINIT, reserve_bootmem_region
+ * is not called during memmap_init_reserved_pages, hence struct pages are not
+ * initialized for this region.
+ *
+ * Return: 0 on success, -errno on failure.
+ */
+int __init_memblock memblock_rsrv_mark_noinit(phys_addr_t base, phys_addr_t size)
+{
+	return memblock_setclr_flag(base, size, 1, MEMBLOCK_RSRV_NOINIT, 1);
+}
+
 static bool should_skip_region(struct memblock_type *type,
 			       struct memblock_region *m,
 			       int nid, int flags)
@@ -2113,13 +2129,17 @@ static void __init memmap_init_reserved_pages(void)
 		memblock_set_node(start, end, &memblock.reserved, nid);
 	}
 
-	/* initialize struct pages for the reserved regions */
+	/*
+	 * initialize struct pages for reserved regions that don't have
+	 * the MEMBLOCK_RSRV_NOINIT flag set
+	 */
 	for_each_reserved_mem_region(region) {
-		nid = memblock_get_region_node(region);
-		start = region->base;
-		end = start + region->size;
-
-		reserve_bootmem_region(start, end, nid);
+		if (!memblock_is_noinit(region)) {
+			nid = memblock_get_region_node(region);
+			start = region->base;
+			end = start + region->size;
+			reserve_bootmem_region(start, end, nid);
+		}
 	}
 }
 
-- 
2.25.1