On Thu, Oct 08, 2020 at 10:25:44AM -0700, Ralph Campbell wrote:
> ZONE_DEVICE struct pages have an extra reference count that complicates the
> code for put_page() and several places in the kernel that need to check the
> reference count to see that a page is not being used (gup, compaction,
> migration, etc.). Clean up the code so the reference count doesn't need to
> be treated specially for device private pages, leaving DAX as still being
> a special case.
What about the check in mc_handle_swap_pte()?
mm/memcontrol.c:
5513 /*
5514 * MEMORY_DEVICE_PRIVATE means ZONE_DEVICE page and which have
5515 * a refcount of 1 when free (unlike normal page)
5516 */
5517 if (!page_ref_add_unless(page, 1, 1))
5518 return NULL;
... does that need to change? Perhaps just the comment?
>
> Signed-off-by: Ralph Campbell <rcampbell@xxxxxxxxxx>
> ---
>
[snip]
>
> void put_devmap_managed_page(struct page *page);
> diff --git a/lib/test_hmm.c b/lib/test_hmm.c
> index e151a7f10519..bf92a261fa6f 100644
> --- a/lib/test_hmm.c
> +++ b/lib/test_hmm.c
> @@ -509,10 +509,15 @@ static bool dmirror_allocate_chunk(struct dmirror_device *mdevice,
> mdevice->devmem_count * (DEVMEM_CHUNK_SIZE / (1024 * 1024)),
> pfn_first, pfn_last);
>
> + /*
> + * Pages are created with an initial reference count of one but should
> + * have a reference count of zero while in the free state.
> + */
> spin_lock(&mdevice->lock);
> for (pfn = pfn_first; pfn < pfn_last; pfn++) {
> struct page *page = pfn_to_page(pfn);
>
> + set_page_count(page, 0);
This confuses me. How does this and init_page_count() not confuse the buddy
allocator? Don't you have to reset the refcount somewhere after the test?
> page->zone_device_data = mdevice->free_pages;
> mdevice->free_pages = page;
> }
> @@ -561,7 +566,7 @@ static struct page *dmirror_devmem_alloc_page(struct dmirror_device *mdevice)
> }
>
> dpage->zone_device_data = rpage;
> - get_page(dpage);
> + init_page_count(dpage);
> lock_page(dpage);
> return dpage;
>
> diff --git a/mm/internal.h b/mm/internal.h
> index c43ccdddb0f6..e1443b73aa9b 100644
> --- a/mm/internal.h
> +++ b/mm/internal.h
>
[snip]
> diff --git a/mm/swap.c b/mm/swap.c
> index 0eb057141a04..93d880c6f73c 100644
> --- a/mm/swap.c
> +++ b/mm/swap.c
> @@ -116,12 +116,11 @@ static void __put_compound_page(struct page *page)
> void __put_page(struct page *page)
> {
> if (is_zone_device_page(page)) {
> - put_dev_pagemap(page->pgmap);
> -
> /*
> * The page belongs to the device that created pgmap. Do
> * not return it to page allocator.
> */
> + free_zone_device_page(page);
I really like this.
Ira
