On Saturday, 27 February 2021 2:59:09 AM AEDT Christoph Hellwig wrote:

quoted

-		struct page *page = migration_entry_to_page(entry);
+		struct page *page = pfn_to_page(swp_offset(entry));

I wonder if keeping a single special_entry_to_page() helper would still
me a useful.  But I'm not entirely sure.  There are also two more open
coded copies of this in the THP migration code.

I think it might be if only to clearly document where these entries are used. 
Will add it for the next version to see what it looks like.

quoted

-#define free_swap_and_cache(e) ({(is_migration_entry(e) || 

is_device_private_entry(e));})

quoted

-#define swapcache_prepare(e) ({(is_migration_entry(e) || 

is_device_private_entry(e));})

quoted

+#define free_swap_and_cache(e) is_special_entry(e)
+#define swapcache_prepare(e) is_special_entry(e)

Staring at this I'm really, really confused at what this is doing.

Looking a little closer these are the !CONFIG_SWAP stubs, but it could
probably use a comment or two.

Will do, thanks.

 - Alistair
 

quoted

 	} else if (is_migration_entry(entry)) {
-		page = migration_entry_to_page(entry);
+		page = pfn_to_page(swp_offset(entry));
 
 		rss[mm_counter(page)]++;
 

@@ -737,7 +737,7 @@ copy_nonpresent_pte(struct mm_struct *dst_mm, struct 

mm_struct *src_mm,

quoted

 			set_pte_at(src_mm, addr, src_pte, pte);
 		}
 	} else if (is_device_private_entry(entry)) {
-		page = device_private_entry_to_page(entry);
+		page = pfn_to_page(swp_offset(entry));
 
 		/*
 		 * Update rss count even for unaddressable pages, as

@@ -1274,7 +1274,7 @@ static unsigned long zap_pte_range(struct mmu_gather 

*tlb,

quoted

 
 		entry = pte_to_swp_entry(ptent);
 		if (is_device_private_entry(entry)) {
-			struct page *page = device_private_entry_to_page(entry);
+			struct page *page = pfn_to_page(swp_offset(entry));
 
 			if (unlikely(details && details->check_mapping)) {
 				/*

@@ -1303,7 +1303,7 @@ static unsigned long zap_pte_range(struct mmu_gather 

*tlb,

quoted

 		else if (is_migration_entry(entry)) {
 			struct page *page;
 
-			page = migration_entry_to_page(entry);
+			page = pfn_to_page(swp_offset(entry));
 			rss[mm_counter(page)]--;
 		}
 		if (unlikely(!free_swap_and_cache(entry)))

@@ -3271,7 +3271,7 @@ vm_fault_t do_swap_page(struct vm_fault *vmf)
 			migration_entry_wait(vma->vm_mm, vmf->pmd,
 					     vmf->address);
 		} else if (is_device_private_entry(entry)) {
-			vmf->page = device_private_entry_to_page(entry);
+			vmf->page = pfn_to_page(swp_offset(entry));
 			ret = vmf->page->pgmap->ops->migrate_to_ram(vmf);
 		} else if (is_hwpoison_entry(entry)) {
 			ret = VM_FAULT_HWPOISON;

diff --git a/mm/migrate.c b/mm/migrate.c
index 20ca887ea769..72adcc3d8f5b 100644
--- a/mm/migrate.c
+++ b/mm/migrate.c

@@ -321,7 +321,7 @@ void __migration_entry_wait(struct mm_struct *mm, 

pte_t *ptep,

quoted

 	if (!is_migration_entry(entry))
 		goto out;
 
-	page = migration_entry_to_page(entry);
+	page = pfn_to_page(swp_offset(entry));
 
 	/*
 	 * Once page cache replacement of page migration started, page_count

@@ -361,7 +361,7 @@ void pmd_migration_entry_wait(struct mm_struct *mm, 

pmd_t *pmd)

quoted

 	ptl = pmd_lock(mm, pmd);
 	if (!is_pmd_migration_entry(*pmd))
 		goto unlock;
-	page = migration_entry_to_page(pmd_to_swp_entry(*pmd));
+	page = pfn_to_page(swp_offset(pmd_to_swp_entry(*pmd)));
 	if (!get_page_unless_zero(page))
 		goto unlock;
 	spin_unlock(ptl);

@@ -2437,7 +2437,7 @@ static int migrate_vma_collect_pmd(pmd_t *pmdp,
 			if (!is_device_private_entry(entry))
 				goto next;
 
-			page = device_private_entry_to_page(entry);
+			page = pfn_to_page(swp_offset(entry));
 			if (!(migrate->flags &
 				MIGRATE_VMA_SELECT_DEVICE_PRIVATE) ||
 			    page->pgmap->owner != migrate->pgmap_owner)

diff --git a/mm/page_vma_mapped.c b/mm/page_vma_mapped.c
index 86e3a3688d59..34230d08556a 100644
--- a/mm/page_vma_mapped.c
+++ b/mm/page_vma_mapped.c

@@ -96,7 +96,7 @@ static bool check_pte(struct page_vma_mapped_walk *pvmw)
 		if (!is_migration_entry(entry))
 			return false;
 
-		pfn = migration_entry_to_pfn(entry);
+		pfn = swp_offset(entry);
 	} else if (is_swap_pte(*pvmw->pte)) {
 		swp_entry_t entry;
 

@@ -105,7 +105,7 @@ static bool check_pte(struct page_vma_mapped_walk 

*pvmw)

quoted

 		if (!is_device_private_entry(entry))
 			return false;
 
-		pfn = device_private_entry_to_pfn(entry);
+		pfn = swp_offset(entry);
 	} else {
 		if (!pte_present(*pvmw->pte))
 			return false;

@@ -200,7 +200,7 @@ bool page_vma_mapped_walk(struct page_vma_mapped_walk 

*pvmw)

quoted

 				if (is_migration_entry(pmd_to_swp_entry(*pvmw->pmd))) {
 					swp_entry_t entry = pmd_to_swp_entry(*pvmw->pmd);
 
-					if (migration_entry_to_page(entry) != page)
+					if (pfn_to_page(swp_offset(entry)) != page)
 						return not_found(pvmw);
 					return true;
 				}

---end quoted text---