search for: expected_page_ref

...a/mm/migrate.c b/mm/migrate.c > > index 2975f0c4d7cf..2e2f41572066 100644 > > --- a/mm/migrate.c > > +++ b/mm/migrate.c > > @@ -336,13 +336,18 @@ void pmd_migration_entry_wait(struct mm_struct *mm, pmd_t *pmd) > > } > > #endif > > > > -static int expected_page_refs(struct address_space *mapping, struct page *page) > > +static int folio_expected_refs(struct address_space *mapping, > > + struct folio *folio) > > { > > - int expected_count = 1; > > + int refs = 1; > > + if (!mapping) > > + return refs; > > &g...

...a/mm/migrate.c b/mm/migrate.c > > index 2975f0c4d7cf..2e2f41572066 100644 > > --- a/mm/migrate.c > > +++ b/mm/migrate.c > > @@ -336,13 +336,18 @@ void pmd_migration_entry_wait(struct mm_struct *mm, pmd_t *pmd) > > } > > #endif > > > > -static int expected_page_refs(struct address_space *mapping, struct page *page) > > +static int folio_expected_refs(struct address_space *mapping, > > + struct folio *folio) > > { > > - int expected_count = 1; > > + int refs = 1; > > + if (!mapping) > > + return refs; > > &g...

...ruct page *page, struct vm_area_struct *vma, if (is_device_private_page(new)) { entry = make_device_private_entry(new, pte_write(pte)); pte = swp_entry_to_pte(entry); - } else if (is_device_public_page(new)) { - pte = pte_mkdevmap(pte); } } @@ -381,7 +379,6 @@ static int expected_page_refs(struct address_space *mapping, struct page *page) * ZONE_DEVICE pages. */ expected_count += is_device_private_page(page); - expected_count += is_device_public_page(page); if (mapping) expected_count += hpage_nr_pages(page) + page_has_private(page); @@ -994,10 +991,7 @@ static int mo...

...ge(page); +} + +void free_zone_device_page(struct page *page) +{ + if (!is_device_private_page(page)) return; - } __ClearPageWaiters(page); diff --git a/mm/migrate.c b/mm/migrate.c index 5ca5842df5db..ee09334b46d8 100644 --- a/mm/migrate.c +++ b/mm/migrate.c @@ -380,11 +380,6 @@ static int expected_page_refs(struct address_space *mapping, struct page *page) { int expected_count = 1; - /* - * Device private pages have an extra refcount as they are - * ZONE_DEVICE pages. - */ - expected_count += is_device_private_page(page); if (mapping) expected_count += thp_nr_pages(page) + page_has_priva...

...eturn; + case MEMORY_DEVICE_PRIVATE: + free_device_private_page(page); + return; + default: + return; + } +} #endif /* CONFIG_DEV_PAGEMAP_OPS */ diff --git a/mm/migrate.c b/mm/migrate.c index aecb1433cf3c..c51749c7cb9d 100644 --- a/mm/migrate.c +++ b/mm/migrate.c @@ -380,11 +380,6 @@ static int expected_page_refs(struct address_space *mapping, struct page *page) { int expected_count = 1; - /* - * Device public or private pages have an extra refcount as they are - * ZONE_DEVICE pages. - */ - expected_count += is_device_private_page(page); if (mapping) expected_count += thp_nr_pages(page) + page...

...eturn; + case MEMORY_DEVICE_PRIVATE: + free_device_private_page(page); + return; + default: + return; + } +} #endif /* CONFIG_DEV_PAGEMAP_OPS */ diff --git a/mm/migrate.c b/mm/migrate.c index 5ca5842df5db..ee09334b46d8 100644 --- a/mm/migrate.c +++ b/mm/migrate.c @@ -380,11 +380,6 @@ static int expected_page_refs(struct address_space *mapping, struct page *page) { int expected_count = 1; - /* - * Device private pages have an extra refcount as they are - * ZONE_DEVICE pages. - */ - expected_count += is_device_private_page(page); if (mapping) expected_count += thp_nr_pages(page) + page_has_priva...

...ge(page); +} + +void free_zone_device_page(struct page *page) +{ + if (!is_device_private_page(page)) return; - } __ClearPageWaiters(page); diff --git a/mm/migrate.c b/mm/migrate.c index 5ca5842df5db..ee09334b46d8 100644 --- a/mm/migrate.c +++ b/mm/migrate.c @@ -380,11 +380,6 @@ static int expected_page_refs(struct address_space *mapping, struct page *page) { int expected_count = 1; - /* - * Device private pages have an extra refcount as they are - * ZONE_DEVICE pages. - */ - expected_count += is_device_private_page(page); if (mapping) expected_count += thp_nr_pages(page) + page_has_priva...

Matthew Wilcox, Ira Weiny, and others have complained that ZONE_DEVICE struct page reference counting is ugly because they are "free" when the reference count is one instead of zero. This leads to explicit checks for ZONE_DEVICE pages in places like put_page(), GUP, THP splitting, and page migration which have to adjust the expected reference count when determining if the page is

This is still an RFC because after looking at the pmem/dax code some more, I realized that the ZONE_DEVICE struct pages are being inserted into the process' page tables with vmf_insert_mixed() and a zero refcount on the ZONE_DEVICE struct page. This is sort of OK because insert_pfn() increments the reference count on the pgmap which is what prevents memunmap_pages() from freeing the struct

...(page); + /* * When a device_private page is freed, the page->mapping field * may still contain a (stale) mapping value. For example, the diff --git a/mm/migrate.c b/mm/migrate.c index 4f89360d9e77..be1586582b52 100644 --- a/mm/migrate.c +++ b/mm/migrate.c @@ -380,11 +380,6 @@ static int expected_page_refs(struct address_space *mapping, struct page *page) { int expected_count = 1; - /* - * Device private pages have an extra refcount as they are - * ZONE_DEVICE pages. - */ - expected_count += is_device_private_page(page); if (mapping) expected_count += thp_nr_pages(page) + page_has_priva...

Hi Dan, Jérôme and Jason, below is a series that cleans up the dev_pagemap interface so that it is more easily usable, which removes the need to wrap it in hmm and thus allowing to kill a lot of code Note: this series is on top of Linux 5.2-rc5 and has some minor conflicts with the hmm tree that are easy to resolve. Diffstat summary: 32 files changed, 361 insertions(+), 1012 deletions(-) Git