On 24/10/2018 06:12, Matthew Wilcox wrote:

On Wed, Oct 24, 2018 at 12:34:55AM +0300, Igor Stoppa wrote:

quoted

The connection between each page and its vmap_area avoids more expensive
searches through the btree of vmap_areas.

Typo -- it's an rbtree.

ack

quoted

+++ b/include/linux/mm_types.h

@@ -87,13 +87,24 @@ struct page {
  			/* See page-flags.h for PAGE_MAPPING_FLAGS */
  			struct address_space *mapping;
  			pgoff_t index;		/* Our offset within mapping. */
-			/**
-			 * @private: Mapping-private opaque data.
-			 * Usually used for buffer_heads if PagePrivate.
-			 * Used for swp_entry_t if PageSwapCache.
-			 * Indicates order in the buddy system if PageBuddy.
-			 */
-			unsigned long private;
+			union {
+				/**
+				 * @private: Mapping-private opaque data.
+				 * Usually used for buffer_heads if
+				 * PagePrivate.
+				 * Used for swp_entry_t if PageSwapCache.
+				 * Indicates order in the buddy system if
+				 * PageBuddy.
+				 */
+				unsigned long private;
+				/**
+				 * @area: reference to the containing area
+				 * For pages that are mapped into a virtually
+				 * contiguous area, avoids performing a more
+				 * expensive lookup.
+				 */
+				struct vmap_area *area;
+			};

Not like this.  Make it part of a different struct in the existing union,
not a part of the pagecache struct.  And there's no need to use ->private
explicitly.

Ok, I'll have a look at the googledoc you made

quoted

@@ -1747,6 +1750,10 @@ void *__vmalloc_node_range(unsigned long size, unsigned long align,
  	if (!addr)
  		return NULL;
  
+	va = __find_vmap_area((unsigned long)addr);
+	for (i = 0; i < va->vm->nr_pages; i++)
+		va->vm->pages[i]->area = va;

I don't like it that you're calling this for _every_ vmalloc() caller
when most of them will never use this.  Perhaps have page->va be initially
NULL and then cache the lookup in it when it's accessed for the first time.

If __find_vmap_area() was part of the API, this loop could be left out 
from __vmalloc_node_range() and the user of the allocation could 
initialize the field, if needed.

What is the reason for keeping __find_vmap_area() private?

--
igor