[PATCH v2 1/2] powerpc/fadump: reserve memory at an offset closer to bottom of RAM

@@ -319,15 +319,34 @@ int __init fadump_reserve_mem(void)
 		pr_debug("fadumphdr_addr = %p\n",
 				(void *) fw_dump.fadumphdr_addr);
 	} else {
-		/* Reserve the memory at the top of memory. */
 		size = get_fadump_area_size();
-		base = memory_boundary - size;
-		memblock_reserve(base, size);
-		printk(KERN_INFO "Reserved %ldMB of memory at %ldMB "
-				"for firmware-assisted dump\n",
-				(unsigned long)(size >> 20),
-				(unsigned long)(base >> 20));
+
+		/*
+		 * Reserve memory at an offset closer to bottom of the RAM to
+		 * minimize the impact of memory hot-remove operation. We can't
+		 * use memblock_find_in_range() here since it doesn't allocate
+		 * from bottom to top.
+		 */
+		for (base = fw_dump.boot_memory_size;
+		     base <= (memory_boundary - size);
+		     base += size) {
+			if (memblock_is_region_memory(base, size) &&
+			    !memblock_is_region_reserved(base, size))
+				break;
+		}
+		if ((base > (memory_boundary - size)) ||
+		    memblock_reserve(base, size)) {
+			pr_err("Failed to reserve memory\n");
+			return 0;
+		}
+
+		pr_info("Reserved %ldMB of memory at %ldMB for firmware-"
+			"assisted dump (System RAM: %ldMB)\n",
+			(unsigned long)(size >> 20),
+			(unsigned long)(base >> 20),
+			(unsigned long)(memblock_phys_mem_size() >> 20));
 	}
+
 	fw_dump.reserve_dump_area_start = base;
 	fw_dump.reserve_dump_area_size = size;
 	return 1;

@@ -105,21 +105,21 @@ memory is held.
 
 If there is no waiting dump data, then only the memory required
 to hold CPU state, HPTE region, boot memory dump and elfcore
-header, is reserved at the top of memory (see Fig. 1). This area
-is *not* released: this region will be kept permanently reserved,
-so that it can act as a receptacle for a copy of the boot memory
-content in addition to CPU state and HPTE region, in the case a
-crash does occur.
+header, is usually reserved at an offset greater than boot memory
+size (see Fig. 1). This area is *not* released: this region will
+be kept permanently reserved, so that it can act as a receptacle
+for a copy of the boot memory content in addition to CPU state
+and HPTE region, in the case a crash does occur.
 
   o Memory Reservation during first kernel
 
-  Low memory                                        Top of memory
+  Low memory                                         Top of memory
   0      boot memory size                                       |
-  |           |                       |<--Reserved dump area -->|
-  V           V                       |   Permanent Reservation V
-  +-----------+----------/ /----------+---+----+-----------+----+
-  |           |                       |CPU|HPTE|  DUMP     |ELF |
-  +-----------+----------/ /----------+---+----+-----------+----+
+  |           |                |<--Reserved dump area -->|      |
+  V           V                |   Permanent Reservation |      V
+  +-----------+----------/ /---+---+----+-----------+----+------+
+  |           |                |CPU|HPTE|  DUMP     |ELF |      |
+  +-----------+----------/ /---+---+----+-----------+----+------+
         |                                           ^
         |                                           |
         \                                           /

@@ -135,12 +135,12 @@ crash does occur.
   0      boot memory size                                       |
   |           |<------------- Reserved dump area ----------- -->|
   V           V                                                 V
-  +-----------+----------/ /----------+---+----+-----------+----+
-  |           |                       |CPU|HPTE|  DUMP     |ELF |
-  +-----------+----------/ /----------+---+----+-----------+----+
-        |                                                    |
-        V                                                    V
-   Used by second                                    /proc/vmcore
+  +-----------+----------/ /---+---+----+-----------+----+------+
+  |           |                |CPU|HPTE|  DUMP     |ELF |      |
+  +-----------+----------/ /---+---+----+-----------+----+------+
+        |                                              |
+        V                                              V
+   Used by second                                /proc/vmcore
    kernel to boot
                    Fig. 2