Andrew,
Please fold it to zsmalloc: page migration support.
Thanks.
On Mon, Jun 13, 2016 at 12:20:15PM +0900, Minchan Kim wrote:
> In early draft of zspage migration, we couldn't use page._mapcount
> because it was used for storing movable flag so we added runtime
> calculation to get first object offset in a page but it causes rather
> many instruction and even bug.
>
> Since then, we don't use page._mapcount as page flag any more so now
> there is no problem to use the field to store first object offset.
>
> Cc: Sergey Senozhatsky <sergey.senozhatsky@xxxxxxxxx>
> Signed-off-by: Minchan Kim <minchan@xxxxxxxxxx>
> ---
> mm/zsmalloc.c | 44 ++++++++++++++++----------------------------
> 1 file changed, 16 insertions(+), 28 deletions(-)
>
> diff --git a/mm/zsmalloc.c b/mm/zsmalloc.c
> index 6a58edc9a015..4b70fcbfb69b 100644
> --- a/mm/zsmalloc.c
> +++ b/mm/zsmalloc.c
> @@ -512,6 +512,16 @@ static inline struct page *get_first_page(struct zspage *zspage)
> return first_page;
> }
>
> +static inline int get_first_obj_offset(struct page *page)
> +{
> + return page->units;
> +}
> +
> +static inline void set_first_obj_offset(struct page *page, int offset)
> +{
> + page->units = offset;
> +}
> +
> static inline unsigned int get_freeobj(struct zspage *zspage)
> {
> return zspage->freeobj;
> @@ -872,31 +882,6 @@ static struct page *get_next_page(struct page *page)
> return page->freelist;
> }
>
> -/* Get byte offset of first object in the @page */
> -static int get_first_obj_offset(struct size_class *class,
> - struct page *first_page, struct page *page)
> -{
> - int pos;
> - int page_idx = 0;
> - int ofs = 0;
> - struct page *cursor = first_page;
> -
> - if (first_page == page)
> - goto out;
> -
> - while (page != cursor) {
> - page_idx++;
> - cursor = get_next_page(cursor);
> - }
> -
> - pos = class->objs_per_zspage * class->size *
> - page_idx / class->pages_per_zspage;
> -
> - ofs = (pos + class->size) % PAGE_SIZE;
> -out:
> - return ofs;
> -}
> -
> /**
> * obj_to_location - get (<page>, <obj_idx>) from encoded object value
> * @page: page object resides in zspage
> @@ -966,6 +951,7 @@ static void reset_page(struct page *page)
> clear_bit(PG_private, &page->flags);
> clear_bit(PG_private_2, &page->flags);
> set_page_private(page, 0);
> + page_mapcount_reset(page);
> ClearPageHugeObject(page);
> page->freelist = NULL;
> }
> @@ -1064,6 +1050,8 @@ static void init_zspage(struct size_class *class, struct zspage *zspage)
> struct link_free *link;
> void *vaddr;
>
> + set_first_obj_offset(page, off);
> +
> vaddr = kmap_atomic(page);
> link = (struct link_free *)vaddr + off / sizeof(*link);
>
> @@ -1762,9 +1750,8 @@ static unsigned long find_alloced_obj(struct size_class *class,
> int offset = 0;
> unsigned long handle = 0;
> void *addr = kmap_atomic(page);
> - struct zspage *zspage = get_zspage(page);
>
> - offset = get_first_obj_offset(class, get_first_page(zspage), page);
> + offset = get_first_obj_offset(page);
> offset += class->size * index;
>
> while (offset < PAGE_SIZE) {
> @@ -1976,6 +1963,7 @@ static void replace_sub_page(struct size_class *class, struct zspage *zspage,
> } while ((page = get_next_page(page)) != NULL);
>
> create_page_chain(class, zspage, pages);
> + set_first_obj_offset(newpage, get_first_obj_offset(oldpage));
> if (unlikely(PageHugeObject(oldpage)))
> newpage->index = oldpage->index;
> __SetPageMovable(newpage, page_mapping(oldpage));
> @@ -2062,7 +2050,7 @@ int zs_page_migrate(struct address_space *mapping, struct page *newpage,
> get_zspage_mapping(zspage, &class_idx, &fullness);
> pool = mapping->private_data;
> class = pool->size_class[class_idx];
> - offset = get_first_obj_offset(class, get_first_page(zspage), page);
> + offset = get_first_obj_offset(page);
>
> spin_lock(&class->lock);
> if (!get_zspage_inuse(zspage)) {
> --
> 1.9.1
>
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