From 1cbab5f2f47ebda5802babd2f94b89f0cf4d8eb3 Mon Sep 17 00:00:00 2001
From: Max Wash <mbswash@gmail.com>
Date: Sun, 24 Dec 2023 09:35:50 +0000
Subject: [PATCH] vm: optimise vm_zone_init by only making blocks from free
 regions during boot

---
 vm/zone.c | 68 ++++++++++++++++++++++++++++++++++++++++++++-----------
 1 file changed, 55 insertions(+), 13 deletions(-)

diff --git a/vm/zone.c b/vm/zone.c
index 3722bd8..96556be 100644
--- a/vm/zone.c
+++ b/vm/zone.c
@@ -104,11 +104,61 @@ void vm_zone_init(struct vm_zone *z, const struct vm_zone_descriptor *zone_info)
 	unsigned long flags;
 	spin_lock_irqsave(&z->z_lock, &flags);
 
-	phys_addr_t block_start = zone_info->zd_base, block_end = zone_info->zd_limit;
-	int this_page_reserved = 0, last_page_reserved = -1;
-
-	phys_addr_t plimit = 0;
 	struct memblock_iter it;
+
+	/* TODO this only creates page blocks for free memory regions, not reserved memory regions.
+	 * this is faster for systems that have huge amounts of reserved memory, but it means
+	 * that a call to vm_page_get() for a reserved memory region will return null
+	 * rather than a reserved page.
+	 *
+	 * vm_page_get() should probably create reserved pages on-demand for these regions. */
+
+	size_t nr_pages_found = 0;
+	for_each_free_mem_range(&it, z->z_info.zd_base, z->z_info.zd_limit) {
+		phys_addr_t block_start = it.it_base, block_end = it.it_limit;
+		int this_page_reserved = 0, last_page_reserved = -1;
+
+		for (uintptr_t i = it.it_base; i < it.it_limit; i += VM_PAGE_SIZE) {
+			struct vm_page *pg = vm_page_get(i);
+
+			if (pg) {
+				nr_pages_found++;
+				this_page_reserved = (pg->p_flags & VM_PAGE_RESERVED) ? 1 : 0;
+			} else {
+				this_page_reserved = 1;
+			}
+
+			if (last_page_reserved == -1) {
+				last_page_reserved = this_page_reserved;
+			}
+
+			if (this_page_reserved == last_page_reserved) {
+				block_end = i;
+				continue;
+			}
+
+			convert_region_to_blocks(
+					z,
+					block_start, block_end + VM_PAGE_SIZE - 1,
+					last_page_reserved);
+
+			block_start = i;
+			last_page_reserved = this_page_reserved;
+		}
+
+		if (block_start != block_end) {
+			/* either the entire zone is homogeneous (all free/all reserved) or the entire zone is empty. */
+			if (nr_pages_found > 0) {
+				/* the entire zone is homogeneous :) */
+				convert_region_to_blocks(
+						z,
+						block_start, block_end + VM_PAGE_SIZE - 1,
+						this_page_reserved);
+			}
+		}
+	}
+
+#if 0
 	for_each_mem_range (&it, 0x00, UINTPTR_MAX) {
 		if (it.it_limit + 1 > plimit) {
 			plimit = it.it_limit + 1;
@@ -119,7 +169,6 @@ void vm_zone_init(struct vm_zone *z, const struct vm_zone_descriptor *zone_info)
 		z->z_info.zd_limit = plimit;
 	}
 
-	size_t nr_pages_found = 0;
 	for (uintptr_t i = z->z_info.zd_base; i < z->z_info.zd_limit; i += VM_PAGE_SIZE) {
 		struct vm_page *pg = vm_page_get(i);
 
@@ -144,14 +193,7 @@ void vm_zone_init(struct vm_zone *z, const struct vm_zone_descriptor *zone_info)
 		block_start = i;
 		last_page_reserved = this_page_reserved;
 	}
-
-	if (block_start != block_end) {
-		/* either the entire zone is homogeneous (all free/all reserved) or the entire zone is empty. */
-		if (nr_pages_found > 0) {
-			/* the entire zone is homogeneous :) */
-			convert_region_to_blocks(z, block_start, block_end + VM_PAGE_SIZE - 1, this_page_reserved);
-		}
-	}
+#endif
 
 	size_t free_bytes = zone_free_bytes(z);
 	spin_unlock_irqrestore(&z->z_lock, flags);