On Tue, Dec 04, 2018 at 04:58:01PM -0800, John Hubbard wrote:
> On 12/4/18 3:03 PM, Dan Williams wrote:
> > Except the LRU fields are already in use for ZONE_DEVICE pages... how
> > does this proposal interact with those?
>
> Very badly: page->pgmap and page->hmm_data both get corrupted. Is there an
> entire
> use case I'm missing: calling get_user_pages() on ZONE_DEVICE pages? Said
> another
> way: is it reasonable to disallow calling get_user_pages() on ZONE_DEVICE
> pages?
>
> If we have to support get_user_pages() on ZONE_DEVICE pages, then the whole
> LRU field approach is unusable.
We just need to rearrange ZONE_DEVICE pages. Please excuse the whitespace
damage:
+++ b/include/linux/mm_types.h
@@ -151,10 +151,12 @@ struct page {
#endif
};
struct { /* ZONE_DEVICE pages */
+ unsigned long _zd_pad_2; /* LRU */
+ unsigned long _zd_pad_3; /* LRU */
+ unsigned long _zd_pad_1; /* uses mapping */
/** @pgmap: Points to the hosting device page map. */
struct dev_pagemap *pgmap;
unsigned long hmm_data;
- unsigned long _zd_pad_1; /* uses mapping */
};
/** @rcu_head: You can use this to free a page by RCU. */
You don't use page->private or page->index, do you Dan?
