From 9879bbf646bbb6edc187ba554cdc8adc6343e57a Mon Sep 17 00:00:00 2001
From: Max Wash <mbswash@gmail.com>
Date: Tue, 7 Feb 2023 15:58:37 +0000
Subject: [PATCH] vm: optimise page array size and initialisation.

* the page array now only extends up to the last non-reserved memory frame.
* rather than memset'ing the whole array to zero, we only initialise p_flags
  for each page in vm_page_array_init, and then leave it to group_pages_into_block
  to initialise the other parts of vm_page_t.
---
 vm/page.c | 14 +++++++-------
 vm/zone.c | 12 +++++++++---
 2 files changed, 16 insertions(+), 10 deletions(-)

diff --git a/vm/page.c b/vm/page.c
index f65d4a5..63a43b7 100644
--- a/vm/page.c
+++ b/vm/page.c
@@ -69,7 +69,7 @@ void vm_page_init_array()
 	size_t pmem_size = 0;
 
 	memblock_iter_t it;
-	for_each_mem_range (&it, 0x0, UINTPTR_MAX) {
+	for_each_free_mem_range (&it, 0x0, UINTPTR_MAX) {
 		if (pmem_size < it.it_limit + 1) {
 			pmem_size = it.it_limit + 1;
 		}
@@ -83,18 +83,18 @@ void vm_page_init_array()
 	page_array = memblock_alloc(sizeof(vm_page_t) * nr_pages, 8);
 	page_array_count = nr_pages;
 
+	size_t nr_reserved = nr_pages;
+
 	for (size_t i = 0; i < nr_pages; i++) {
-		memset(&page_array[i], 0x0, sizeof page_array[i]);
+		page_array[i].p_flags = VM_PAGE_RESERVED;
 	}
 
-	size_t nr_reserved = 0;
-
-	for_each_reserved_mem_range(&it, 0x0, UINTPTR_MAX) {
+	for_each_free_mem_range(&it, 0x0, UINTPTR_MAX) {
 		for (uintptr_t i = it.it_base; i < it.it_limit; i += VM_PAGE_SIZE) {
 			size_t pfn = i / VM_PAGE_SIZE;
 
-			page_array[pfn].p_flags |= VM_PAGE_RESERVED;
-			nr_reserved++;
+			page_array[pfn].p_flags = 0;
+			nr_reserved--;
 		}
 	}
 
diff --git a/vm/zone.c b/vm/zone.c
index 5eb0866..3f54d89 100644
--- a/vm/zone.c
+++ b/vm/zone.c
@@ -10,6 +10,13 @@ static vm_page_t *group_pages_into_block(vm_zone_t *z, phys_addr_t base, phys_ad
 	vm_page_t *first_page = NULL;
 	for (phys_addr_t i = base; i < limit; i += VM_PAGE_SIZE) {
 		vm_page_t *pg = vm_page_get(i);
+		/* p_flags is the only part of the page that has been
+		   initialised at this point. */
+
+		pg->p_order = order;
+		pg->p_node = z->z_info.zd_node;
+		pg->p_zone = z->z_info.zd_id;
+		pg->p_reserved = 0;
 
 		if (order != VM_PAGE_MIN_ORDER) {
 			pg->p_flags |= VM_PAGE_HUGE;
@@ -20,9 +27,8 @@ static vm_page_t *group_pages_into_block(vm_zone_t *z, phys_addr_t base, phys_ad
 			first_page = pg;
 		}
 
-		pg->p_order = order;
-		pg->p_node = z->z_info.zd_node;
-		pg->p_zone = z->z_info.zd_id;
+		pg->p_list = QUEUE_ENTRY_INIT;
+		pg->p_slab = NULL;
 	}
 
 	return first_page;