Re: [PATCH 10/11] x86, mem-hotplug: Support initialize page tables from low to high.

[Wanpeng Li <liwanp@linux.vnet.ibm.com>]

Hi Tang,
On Tue, Aug 27, 2013 at 05:37:47PM +0800, Tang Chen wrote:
>init_mem_mapping() is called before SRAT is parsed. And memblock will allocate
>memory for page tables. To prevent page tables being allocated within hotpluggable
>memory, we will allocate page tables from the end of kernel image to the higher
>memory.
>
>The order of page tables allocation is controled by movablenode boot option.
>Since the default behavior of page tables initialization procedure is allocate
>page tables from top of the memory downwards, if users don't specify movablenode
>boot option, the kernel will behave as before.
>
>Signed-off-by: Tang Chen <tangchen@cn.fujitsu.com>
>Reviewed-by: Zhang Yanfei <zhangyanfei@cn.fujitsu.com>
>---
> arch/x86/mm/init.c |  119 +++++++++++++++++++++++++++++++++++++++------------
> 1 files changed, 91 insertions(+), 28 deletions(-)
>
>diff --git a/arch/x86/mm/init.c b/arch/x86/mm/init.c
>index 793204b..f004d8e 100644
>--- a/arch/x86/mm/init.c
>+++ b/arch/x86/mm/init.c
>@@ -407,13 +407,77 @@ static unsigned long __init init_range_memory_mapping(
>
> /* (PUD_SHIFT-PMD_SHIFT)/2 */
> #define STEP_SIZE_SHIFT 5
>-void __init init_mem_mapping(void)
>+
>+#ifdef CONFIG_MOVABLE_NODE
>+/**
>+ * memory_map_from_low - Map [start, end) from low to high
>+ * @start: start address of the target memory range
>+ * @end: end address of the target memory range
>+ *
>+ * This function will setup direct mapping for memory range [start, end) in a
>+ * heuristic way. In the beginning, step_size is small. The more memory we map
>+ * memory in the next loop.
>+ */
>+static void __init memory_map_from_low(unsigned long start, unsigned long end)
>+{
>+	unsigned long next, new_mapped_ram_size;
>+	unsigned long mapped_ram_size = 0;
>+	/* step_size need to be small so pgt_buf from BRK could cover it */
>+	unsigned long step_size = PMD_SIZE;
>+
>+	while (start < end) {
>+		if (end - start > step_size) {
>+			next = round_up(start + 1, step_size);
>+			if (next > end)
>+				next = end;
>+		} else
>+			next = end;
>+
>+		new_mapped_ram_size = init_range_memory_mapping(start, next);
>+		start = next;
>+
>+		if (new_mapped_ram_size > mapped_ram_size)
>+			step_size <<= STEP_SIZE_SHIFT;
>+		mapped_ram_size += new_mapped_ram_size;
>+	}
>+}
>+#endif /* CONFIG_MOVABLE_NODE */
>+
>+/**
>+ * memory_map_from_high - Map [start, end) from high to low
>+ * @start: start address of the target memory range
>+ * @end: end address of the target memory range
>+ *
>+ * This function is similar to memory_map_from_low() except it maps memory
>+ * from high to low.
>+ */
>+static void __init memory_map_from_high(unsigned long start, unsigned long end)
> {
>-	unsigned long end, real_end, start, last_start;
>-	unsigned long step_size;
>-	unsigned long addr;
>+	unsigned long prev, new_mapped_ram_size;
> 	unsigned long mapped_ram_size = 0;
>-	unsigned long new_mapped_ram_size;
>+	/* step_size need to be small so pgt_buf from BRK could cover it */
>+	unsigned long step_size = PMD_SIZE;
>+
>+	while (start < end) {
>+		if (end > step_size) {
>+			prev = round_down(end - 1, step_size);
>+			if (prev < start)
>+				prev = start;
>+		} else
>+			prev = start;
>+
>+		new_mapped_ram_size = init_range_memory_mapping(prev, end);
>+		end = prev;
>+
>+		if (new_mapped_ram_size > mapped_ram_size)
>+			step_size <<= STEP_SIZE_SHIFT;
>+		mapped_ram_size += new_mapped_ram_size;
>+	}
>+}
>+
>+void __init init_mem_mapping(void)
>+{
>+	unsigned long end;
>
> 	probe_page_size_mask();
>
>@@ -423,44 +487,43 @@ void __init init_mem_mapping(void)
> 	end = max_low_pfn << PAGE_SHIFT;
> #endif
>
>-	/* the ISA range is always mapped regardless of memory holes */
>-	init_memory_mapping(0, ISA_END_ADDRESS);
>+	max_pfn_mapped = 0; /* will get exact value next */
>+	min_pfn_mapped = end >> PAGE_SHIFT;
>+
>+#ifdef CONFIG_MOVABLE_NODE
>+	unsigned long kernel_end;
>+
>+	if (movablenode_enable_srat &&
>+	    memblock.current_order == MEMBLOCK_ORDER_LOW_TO_HIGH) {

I think memblock.current_order == MEMBLOCK_ORDER_LOW_TO_HIGH is always
true if config MOVABLE_NODE and movablenode_enable_srat == true if PATCH
11/11 is applied.

>+		kernel_end = round_up(__pa_symbol(_end), PMD_SIZE);
>+
>+		memory_map_from_low(kernel_end, end);
>+		memory_map_from_low(ISA_END_ADDRESS, kernel_end);

Why split ISA_END_ADDRESS ~ end? 

>+		goto out;
>+	}
>+#endif /* CONFIG_MOVABLE_NODE */
>+
>+	unsigned long addr, real_end;
>
> 	/* xen has big range in reserved near end of ram, skip it at first.*/
> 	addr = memblock_find_in_range(ISA_END_ADDRESS, end, PMD_SIZE, PMD_SIZE);
> 	real_end = addr + PMD_SIZE;
>
>-	/* step_size need to be small so pgt_buf from BRK could cover it */
>-	step_size = PMD_SIZE;
>-	max_pfn_mapped = 0; /* will get exact value next */
>-	min_pfn_mapped = real_end >> PAGE_SHIFT;
>-	last_start = start = real_end;
>-
> 	/*
> 	 * We start from the top (end of memory) and go to the bottom.
> 	 * The memblock_find_in_range() gets us a block of RAM from the
> 	 * end of RAM in [min_pfn_mapped, max_pfn_mapped) used as new pages
> 	 * for page table.
> 	 */
>-	while (last_start > ISA_END_ADDRESS) {
>-		if (last_start > step_size) {
>-			start = round_down(last_start - 1, step_size);
>-			if (start < ISA_END_ADDRESS)
>-				start = ISA_END_ADDRESS;
>-		} else
>-			start = ISA_END_ADDRESS;
>-		new_mapped_ram_size = init_range_memory_mapping(start,
>-							last_start);
>-		last_start = start;
>-		/* only increase step_size after big range get mapped */
>-		if (new_mapped_ram_size > mapped_ram_size)
>-			step_size <<= STEP_SIZE_SHIFT;
>-		mapped_ram_size += new_mapped_ram_size;
>-	}

I think the variables sorted by address is:
ISA_END_ADDRESS -> _end -> real_end -> end 

>+	memory_map_from_high(ISA_END_ADDRESS, real_end);

If this is overlap with work done between #ifdef CONFIG_MOVABLE_NODE and
#endif?

Regards,
Wanpeng LI 

>
> 	if (real_end < end)
> 		init_range_memory_mapping(real_end, end);
>
>+out:
>+	/* the ISA range is always mapped regardless of memory holes */
>+	init_memory_mapping(0, ISA_END_ADDRESS);
>+
> #ifdef CONFIG_X86_64
> 	if (max_pfn > max_low_pfn) {
> 		/* can we preseve max_low_pfn ?*/
>-- 
>1.7.1
>
>--
>To unsubscribe, send a message with 'unsubscribe linux-mm' in
>the body to majordomo@kvack.org.  For more info on Linux MM,
>see: http://www.linux-mm.org/ .
>Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a>

--
To unsubscribe, send a message with 'unsubscribe linux-mm' in
the body to majordomo@kvack.org.  For more info on Linux MM,
see: http://www.linux-mm.org/ .
Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a>