On Wed, Nov 13, 2019 at 04:07:22PM -0800, Dan Williams wrote:
>  static int devmap_managed_enable_get(struct dev_pagemap *pgmap)
>  {
> -     if (!pgmap->ops || !pgmap->ops->page_free) {
> +     if (!pgmap->ops || (pgmap->type == MEMORY_DEVICE_PRIVATE
> +                             && !pgmap->ops->page_free)) {

I don't think this check is correct.  You only want the the ops null check
or MEMORY_DEVICE_PRIVATE as well now, i.e.:

        if (pgmap->type == MEMORY_DEVICE_PRIVATE &&
            (!pgmap->ops || !pgmap->ops->page_free)) {

> @@ -476,10 +471,17 @@ void __put_devmap_managed_page(struct page *page)
>                * handled differently or not done at all, so there is no need
>                * to clear page->mapping.
>                */
> -             if (is_device_private_page(page))
> -                     page->mapping = NULL;
> +             if (is_device_private_page(page)) {
> +                     /* Clear Active bit in case of parallel 
> mark_page_accessed */

This adds a > 80 char line.  But that whole flow of the function seems
rather odd now.

Why can't we do:

        if (count == 0) {
                __put_page(page);
        } else if (is_device_private_page(page)) {
                __ClearPageActive(page);
                __ClearPageWaiters(page);

                mem_cgroup_uncharge(page);
                page->mapping = NULL;
                page->pgmap->ops->page_free(page);
        } else {
                wake_up_var(&page->_refcount);
        }

(except for the fact that I don't get the point of calling __put_page
on a refcount of zero, but that is separate from this patch).
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