On 11/6/20 4:14 AM, Matthew Wilcox wrote:
On Thu, Nov 05, 2020 at 04:51:42PM -0800, Ralph Campbell wrote:
Add a helper function to allow device drivers to create device private
transparent huge pages. This is intended to help support device private
THP migrations.
I think you'd be better off with these calling conventions:
-void prep_transhuge_page(struct page *page)
+struct page *thp_prep(struct page *page)
{
+ if (!page || compound_order(page) == 0)
+ return page;
/*
- * we use page->mapping and page->indexlru in second tail page
+ * we use page->mapping and page->index in second tail page
* as list_head: assuming THP order >= 2
*/
+ BUG_ON(compound_order(page) == 1);
INIT_LIST_HEAD(page_deferred_list(page));
set_compound_page_dtor(page, TRANSHUGE_PAGE_DTOR);
+
+ return page;
}
It simplifies the users.
I'm not sure what the simplification is.
If you mean the name change from prep_transhuge_page() to thp_prep(),
that seems fine to me. The following could also be renamed to
thp_prep_device_private_page() or similar.
+void prep_transhuge_device_private_page(struct page *page)
+{
+ prep_compound_page(page, HPAGE_PMD_ORDER);
+ prep_transhuge_page(page);
+ /* Only the head page has a reference to the pgmap. */
+ percpu_ref_put_many(page->pgmap->ref, HPAGE_PMD_NR - 1);
+}
+EXPORT_SYMBOL_GPL(prep_transhuge_device_private_page);
Something else that may interest you from my patch series is support
for page sizes other than PMD_SIZE. I don't know what page sizes
hardware supports. There's no support for page sizes other than PMD
for anonymous memory, so this might not be too useful for you yet.
I did see those changes. It might help some device drivers to do DMA in
larger than PAGE_SIZE blocks but less than PMD_SIZE. It might help
reduce page table sizes since 2MB, 64K, and 4K are commonly supported
GPU page sizes. The MIGRATE_PFN_COMPOUND flag is intended to indicate
that the page size is determined by page_size() so I was thinking ahead
to other than PMD sized pages. However, when migrating a pte_none() or
pmd_none() page, there is no source page to determine the size.
Maybe I need to encode the page order in the migrate PFN entry like
hmm_range_fault().
Anyway, I agree that thinking about page sizes other than PMD is good.
