On Thu, Oct 11, 2018 at 11:00:12PM -0700, john.hubbard@xxxxxxxxx wrote:
> From: John Hubbard <jhubbard@xxxxxxxxxx>
>
> Add two struct page fields that, combined, are unioned with
> struct page->lru. There is no change in the size of
> struct page. These new fields are for type safety and clarity.
>
> Also add page flag accessors to test, set and clear the new
> page->dma_pinned_flags field.
>
> The page->dma_pinned_count field will be used in upcoming
> patches
>
> Signed-off-by: John Hubbard <jhubbard@xxxxxxxxxx>
> ---
> include/linux/mm_types.h | 22 +++++++++++++-----
> include/linux/page-flags.h | 47 ++++++++++++++++++++++++++++++++++++++
> 2 files changed, 63 insertions(+), 6 deletions(-)
>
> diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h
> index 5ed8f6292a53..017ab82e36ca 100644
> --- a/include/linux/mm_types.h
> +++ b/include/linux/mm_types.h
> @@ -78,12 +78,22 @@ struct page {
> */
> union {
> struct { /* Page cache and anonymous pages */
> - /**
> - * @lru: Pageout list, eg. active_list protected by
> - * zone_lru_lock. Sometimes used as a generic list
> - * by the page owner.
> - */
> - struct list_head lru;
> + union {
> + /**
> + * @lru: Pageout list, eg. active_list protected
> + * by zone_lru_lock. Sometimes used as a
> + * generic list by the page owner.
> + */
> + struct list_head lru;
> + /* Used by get_user_pages*(). Pages may not be
> + * on an LRU while these dma_pinned_* fields
> + * are in use.
> + */
> + struct {
> + unsigned long dma_pinned_flags;
> + atomic_t dma_pinned_count;
> + };
> + };
Isn't this broken for mapped file-backed pages? i.e. they may be
passed as the user buffer to read/write direct IO and so the pages
passed to gup will be on the active/inactive LRUs. hence I can't see
how you can have dual use of the LRU list head like this....
What am I missing here?
Cheers,
Dave.
--
Dave Chinner
david@xxxxxxxxxxxxx
