[RFC PATCH 6/8] mm/vmalloc: align vm_area so vmap() can batch mappings

["Barry Song (Xiaomi)" <baohua@kernel.org>]

Try to align the vmap virtual address to PMD_SHIFT or a
larger PTE mapping size hinted by the architecture, so
contiguous pages can be batch-mapped when setting PMD or
PTE entries.

Signed-off-by: Barry Song (Xiaomi) <baohua@kernel.org>
---
 mm/vmalloc.c | 31 ++++++++++++++++++++++++++++++-
 1 file changed, 30 insertions(+), 1 deletion(-)

diff --git a/mm/vmalloc.c b/mm/vmalloc.c
index e8dbfada42bc..6643ec0288cd 100644
--- a/mm/vmalloc.c
+++ b/mm/vmalloc.c
@@ -3576,6 +3576,35 @@ static int vmap_contig_pages_range(unsigned long addr, unsigned long end,
 	return err;
 }
 
+static struct vm_struct *get_aligned_vm_area(unsigned long size, unsigned long flags)
+{
+	unsigned int shift = (size >= PMD_SIZE) ? PMD_SHIFT :
+				arch_vmap_pte_supported_shift(size);
+	struct vm_struct *vm_area = NULL;
+
+	/*
+	 * Try to allocate an aligned vm_area so contiguous pages can be
+	 * mapped in batches.
+	 */
+	while (1) {
+		unsigned long align = 1UL << shift;
+
+		vm_area =  __get_vm_area_node(size, align, PAGE_SHIFT, flags,
+				VMALLOC_START, VMALLOC_END,
+				NUMA_NO_NODE, GFP_KERNEL,
+				__builtin_return_address(0));
+		if (vm_area || shift <= PAGE_SHIFT)
+			goto out;
+		if (shift == PMD_SHIFT)
+			shift = arch_vmap_pte_supported_shift(size);
+		else if (shift > PAGE_SHIFT)
+			shift = PAGE_SHIFT;
+	}
+
+out:
+	return vm_area;
+}
+
 /**
  * vmap - map an array of pages into virtually contiguous space
  * @pages: array of page pointers
@@ -3614,7 +3643,7 @@ void *vmap(struct page **pages, unsigned int count,
 		return NULL;
 
 	size = (unsigned long)count << PAGE_SHIFT;
-	area = get_vm_area_caller(size, flags, __builtin_return_address(0));
+	area = get_aligned_vm_area(size, flags);
 	if (!area)
 		return NULL;
 
-- 
2.39.3 (Apple Git-146)