On 6/21/20 4:20 PM, Zi Yan wrote:
On 19 Jun 2020, at 17:56, Ralph Campbell wrote:Support transparent huge page migration to ZONE_DEVICE private memory. A new flag (MIGRATE_PFN_COMPOUND) is added to the input PFN array to indicate the huge page was fully mapped by the CPU. Export prep_compound_page() so that device drivers can create huge device private pages after calling memremap_pages(). Signed-off-by: Ralph Campbell <rcampbell@xxxxxxxxxx> --- include/linux/migrate.h | 1 + include/linux/mm.h | 1 + mm/huge_memory.c | 30 ++++-- mm/internal.h | 1 - mm/memory.c | 10 +- mm/memremap.c | 9 +- mm/migrate.c | 226 ++++++++++++++++++++++++++++++++-------- mm/page_alloc.c | 1 + 8 files changed, 226 insertions(+), 53 deletions(-) diff --git a/include/linux/migrate.h b/include/linux/migrate.h index 3e546cbf03dd..f6a64965c8bd 100644 --- a/include/linux/migrate.h +++ b/include/linux/migrate.h @@ -166,6 +166,7 @@ static inline int migrate_misplaced_transhuge_page(struct mm_struct *mm, #define MIGRATE_PFN_MIGRATE (1UL << 1) #define MIGRATE_PFN_LOCKED (1UL << 2) #define MIGRATE_PFN_WRITE (1UL << 3) +#define MIGRATE_PFN_COMPOUND (1UL << 4) #define MIGRATE_PFN_SHIFT 6 static inline struct page *migrate_pfn_to_page(unsigned long mpfn) diff --git a/include/linux/mm.h b/include/linux/mm.h index dc7b87310c10..020b9dd3cddb 100644 --- a/include/linux/mm.h +++ b/include/linux/mm.h @@ -932,6 +932,7 @@ static inline unsigned int page_shift(struct page *page) } void free_compound_page(struct page *page); +void prep_compound_page(struct page *page, unsigned int order); #ifdef CONFIG_MMU /* diff --git a/mm/huge_memory.c b/mm/huge_memory.c index 78c84bee7e29..25d95f7b1e98 100644 --- a/mm/huge_memory.c +++ b/mm/huge_memory.c @@ -1663,23 +1663,35 @@ int zap_huge_pmd(struct mmu_gather *tlb, struct vm_area_struct *vma, } else { struct page *page = NULL; int flush_needed = 1; + bool is_anon = false; if (pmd_present(orig_pmd)) { page = pmd_page(orig_pmd); + is_anon = PageAnon(page); page_remove_rmap(page, true); VM_BUG_ON_PAGE(page_mapcount(page) < 0, page); VM_BUG_ON_PAGE(!PageHead(page), page); } else if (thp_migration_supported()) { swp_entry_t entry; - VM_BUG_ON(!is_pmd_migration_entry(orig_pmd)); entry = pmd_to_swp_entry(orig_pmd); - page = pfn_to_page(swp_offset(entry)); + if (is_device_private_entry(entry)) { + page = device_private_entry_to_page(entry); + is_anon = PageAnon(page); + page_remove_rmap(page, true); + VM_BUG_ON_PAGE(page_mapcount(page) < 0, page); + VM_BUG_ON_PAGE(!PageHead(page), page); + put_page(page);Why do you hide this code behind thp_migration_supported()? It seems that you just need pmd swap entry not pmd migration entry. Also the condition is not consistent with the code in __handle_mm_fault(), in which you handle is_device_private_entry() directly without checking thp_migration_support().
Good point, I think "else if (thp_migration_supported())" should be "else if (is_pmd_migration_entry(orig_pmd))" since if the PMD *is* a device private or migration entry, then it should be handled and the VM_BUG_ON() should be that thp_migration_supported() is true (or maybe remove the VM_BUG_ON?).
Do we need to support split_huge_pmd() if a page is migrated to device? Any new code needed in split_huge_pmd()?
I was thinking that any CPU usage of the device private page would cause it to be migrated back to system memory as a whole PMD/PUD page but I'll double check. At least there should be a check that the page isn't a device private page.
