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SubjectRe: [PATCH 08/17] prmem: struct page: track vmap_area
On Wed, Oct 24, 2018 at 12:34:55AM +0300, Igor Stoppa wrote:
> The connection between each page and its vmap_area avoids more expensive
> searches through the btree of vmap_areas.

Typo -- it's an rbtree.

> +++ 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.

> @@ -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.

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