[PATCH v3 02/17] memblock: Declare scratch memory as CMA

[Alexander Graf <graf@amazon.com>]

When we finish populating our memory, we don't want to lose the scratch
region as memory we can use for useful data. Do do that, we mark it as
CMA memory. That means that any allocation within it only happens with
movable memory which we can then happily discard for the next kexec.

That way we don't lose the scratch region's memory anymore for
allocations after boot.

Signed-off-by: Alexander Graf <graf@amazon.com>

---

v1 -> v2:

  - test bot warning fix

v2 -> v3:

  - s/reserve_scratch_mem/mark_phys_as_cma/
  - Declare scratch memory as CMA: Remove ifdeffery
  - Declare scratch memory as CMA: Remove superfluous comment
---
 mm/memblock.c | 26 ++++++++++++++++++++++----
 1 file changed, 22 insertions(+), 4 deletions(-)

diff --git a/mm/memblock.c b/mm/memblock.c
index fbb98981a202..56530d0469a8 100644
--- a/mm/memblock.c
+++ b/mm/memblock.c
@@ -16,6 +16,7 @@
 #include <linux/kmemleak.h>
 #include <linux/seq_file.h>
 #include <linux/memblock.h>
+#include <linux/page-isolation.h>
 
 #include <asm/sections.h>
 #include <linux/io.h>
@@ -1134,10 +1135,6 @@ static bool should_skip_region(struct memblock_type *type,
 	if ((flags & MEMBLOCK_SCRATCH) && !memblock_is_scratch(m))
 		return true;
 
-	/* Leave scratch memory alone after scratch-only phase */
-	if (!(flags & MEMBLOCK_SCRATCH) && memblock_is_scratch(m))
-		return true;
-
 	return false;
 }
 
@@ -2188,6 +2185,16 @@ static void __init __free_pages_memory(unsigned long start, unsigned long end)
 	}
 }
 
+static void mark_phys_as_cma(phys_addr_t start, phys_addr_t end)
+{
+	ulong start_pfn = pageblock_start_pfn(PFN_DOWN(start));
+	ulong end_pfn = pageblock_align(PFN_UP(end));
+	ulong pfn;
+
+	for (pfn = start_pfn; pfn < end_pfn; pfn += pageblock_nr_pages)
+		set_pageblock_migratetype(pfn_to_page(pfn), MIGRATE_CMA);
+}
+
 static unsigned long __init __free_memory_core(phys_addr_t start,
 				 phys_addr_t end)
 {
@@ -2249,6 +2256,17 @@ static unsigned long __init free_low_memory_core_early(void)
 
 	memmap_init_reserved_pages();
 
+	if (IS_ENABLED(CONFIG_MEMBLOCK_SCRATCH)) {
+		/*
+		 * Mark scratch mem as CMA before we return it. That way we
+		 * ensure that no kernel allocations happen on it. That means
+		 * we can reuse it as scratch memory again later.
+		 */
+		__for_each_mem_range(i, &memblock.memory, NULL, NUMA_NO_NODE,
+				     MEMBLOCK_SCRATCH, &start, &end, NULL)
+			mark_phys_as_cma(start, end);
+	}
+
 	/*
 	 * We need to use NUMA_NO_NODE instead of NODE_DATA(0)->node_id
 	 *  because in some case like Node0 doesn't have RAM installed
-- 
2.40.1




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