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

...

• 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.

...

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

is_device_private_entry(e));})

...

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

is_device_private_entry(e));})

...

+#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

...

} 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,

...

	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,

...

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,

...

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,

...

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)

...

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)

...

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)

...

		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;
  	}
  

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