[PATCHv9 03/14] mm/page_alloc: Fake unaccepted memory

[Kirill A. Shutemov]

For testing purposes, it is useful to fake unaccepted memory in the
system. It helps to understand unaccepted memory overhead to the page
allocator.

The patch allows to treat memory above the specified physical memory
address as unaccepted.

The change only fakes unaccepted memory for page allocator. Memblock is
not affected.

It also assumes that arch-provided accept_memory() on already accepted
memory is a nop.

Signed-off-by: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
---
 mm/page_alloc.c | 21 +++++++++++++++++++++
 1 file changed, 21 insertions(+)

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index d62fcb2f28bd..509a93b7e5af 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -7213,6 +7213,8 @@ static DEFINE_STATIC_KEY_FALSE(zones_with_unaccepted_pages);
 
 static bool lazy_accept = true;
 
+static unsigned long fake_unaccepted_start = -1UL;
+
 static int __init accept_memory_parse(char *p)
 {
 	if (!strcmp(p, "lazy")) {
@@ -7227,11 +7229,30 @@ static int __init accept_memory_parse(char *p)
 }
 early_param("accept_memory", accept_memory_parse);
 
+static int __init fake_unaccepted_start_parse(char *p)
+{
+	if (!p)
+		return -EINVAL;
+
+	fake_unaccepted_start = memparse(p, &p);
+
+	if (*p != '\0') {
+		fake_unaccepted_start = -1UL;
+		return -EINVAL;
+	}
+
+	return 0;
+}
+early_param("fake_unaccepted_start", fake_unaccepted_start_parse);
+
 static bool page_contains_unaccepted(struct page *page, unsigned int order)
 {
 	phys_addr_t start = page_to_phys(page);
 	phys_addr_t end = start + (PAGE_SIZE << order);
 
+	if (start >= fake_unaccepted_start)
+		return true;
+
 	return range_contains_unaccepted_memory(start, end);
 }
 
-- 
2.39.2