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Subject: [PATCH 02/15] memblock: Declare scratch memory as CMA
Date:   Wed, 13 Dec 2023 00:04:39 +0000
Message-ID: <20231213000452.88295-3-graf@amazon.com>
In-Reply-To: <20231213000452.88295-1-graf@amazon.com>
References: <20231213000452.88295-1-graf@amazon.com>
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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>
---
 mm/memblock.c | 30 ++++++++++++++++++++++++++----
 1 file changed, 26 insertions(+), 4 deletions(-)

diff --git a/mm/memblock.c b/mm/memblock.c
index e89e6c8f9d75..44741424dab7 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>
@@ -1100,10 +1101,6 @@ 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;
 }
 
@@ -2153,6 +2150,20 @@ static void __init __free_pages_memory(unsigned long start, unsigned long end)
 	}
 }
 
+static void reserve_scratch_mem(phys_addr_t start, phys_addr_t end)
+{
+#ifdef CONFIG_MEMBLOCK_SCRATCH
+	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) {
+		/* Mark as CMA to prevent kernel allocations in it */
+		set_pageblock_migratetype(pfn_to_page(pfn), MIGRATE_CMA);
+	}
+#endif
+}
+
 static unsigned long __init __free_memory_core(phys_addr_t start,
 				 phys_addr_t end)
 {
@@ -2214,6 +2225,17 @@ static unsigned long __init free_low_memory_core_early(void)
 
 	memmap_init_reserved_pages();
 
+#ifdef 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)
+		reserve_scratch_mem(start, end);
+#endif
+
 	/*
 	 * 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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