[PATCH v1 38/39] mm: convert page_try_share_anon_rmap() to folio_try_share_anon_rmap_[pte|pmd]()

David Hildenbrand
2023-12-11T16:00:04Z

Let's convert it like we converted all the other rmap functions.
Don't introduce folio_try_share_anon_rmap_ptes() for now, as we don't
have a user that wants rmap batching in sight. Pretty easy to add later.

All users are easy to convert -- only ksm.c doesn't use folios yet but
that is left for future work -- so let's just do it in a single shot.

While at it, turn the BUG_ON into a WARN_ON_ONCE.

Note that page_try_share_anon_rmap() so far didn't care about pte/pmd
mappings (no compound parameter). We're changing that so we can perform
better sanity checks and make the code actually more readable/consistent.
For example, __folio_rmap_sanity_checks() will make sure that a PMD
range actually falls completely into the folio.

Signed-off-by: David Hildenbrand <david@redhat.com>
---
include/linux/rmap.h | 95 +++++++++++++++++++++++++++++++++-----------
mm/gup.c | 2 +-
mm/huge_memory.c | 9 +++--
mm/internal.h | 4 +-
mm/ksm.c | 5 ++-
mm/migrate_device.c | 2 +-
mm/rmap.c | 11 ++---
7 files changed, 89 insertions(+), 39 deletions(-)

diff --git a/include/linux/rmap.h b/include/linux/rmap.h
index 1e37ee6ae0ba..1e54a28cc884 100644
--- a/include/linux/rmap.h
+++ b/include/linux/rmap.h
@@ -272,7 +272,7 @@ static inline int hugetlb_try_dup_anon_rmap(struct folio *folio,
return 0;
}

-/* See page_try_share_anon_rmap() */
+/* See folio_try_share_anon_rmap_*() */
static inline int hugetlb_try_share_anon_rmap(struct folio *folio)
{
VM_WARN_ON_FOLIO(!folio_test_hugetlb(folio), folio);
@@ -481,30 +481,15 @@ static inline int folio_try_dup_anon_rmap_pmd(struct folio *folio,
#endif
}

-/**
- * page_try_share_anon_rmap - try marking an exclusive anonymous page possibly
- * shared to prepare for KSM or temporary unmapping
- * @page: the exclusive anonymous page to try marking possibly shared
- *
- * The caller needs to hold the PT lock and has to have the page table entry
- * cleared/invalidated.
- *
- * This is similar to folio_try_dup_anon_rmap_*(), however, not used during
- * fork() to duplicate a mapping, but instead to prepare for KSM or temporarily
- * unmapping a page (swap, migration) via folio_remove_rmap_*().
- *
- * Marking the page shared can only fail if the page may be pinned; device
- * private pages cannot get pinned and consequently this function cannot fail.
- *
- * Returns 0 if marking the page possibly shared succeeded. Returns -EBUSY
- * otherwise.
- */
-static inline int page_try_share_anon_rmap(struct page *page)
+static __always_inline int __folio_try_share_anon_rmap(struct folio *folio,
+ struct page *page, int nr_pages, enum rmap_mode mode)
{
- VM_BUG_ON_PAGE(!PageAnon(page) || !PageAnonExclusive(page), page);
+ VM_WARN_ON_FOLIO(!folio_test_anon(folio), folio);
+ VM_WARN_ON_FOLIO(!PageAnonExclusive(page), folio);
+ __folio_rmap_sanity_checks(folio, page, nr_pages, mode);

- /* device private pages cannot get pinned via GUP. */
- if (unlikely(is_device_private_page(page))) {
+ /* device private folios cannot get pinned via GUP. */
+ if (unlikely(folio_is_device_private(folio))) {
ClearPageAnonExclusive(page);
return 0;
}
@@ -555,7 +540,7 @@ static inline int page_try_share_anon_rmap(struct page *page)
if (IS_ENABLED(CONFIG_HAVE_FAST_GUP))
smp_mb();

- if (unlikely(page_maybe_dma_pinned(page)))
+ if (unlikely(folio_maybe_dma_pinned(folio)))
return -EBUSY;
ClearPageAnonExclusive(page);

@@ -568,6 +553,68 @@ static inline int page_try_share_anon_rmap(struct page *page)
return 0;
}

+/**
+ * folio_try_share_anon_rmap_pte - try marking an exclusive anonymous page
+ * mapped by a PTE possibly shared to prepare
+ * for KSM or temporary unmapping
+ * @folio: The folio to share a mapping of
+ * @page: The mapped exclusive page
+ *
+ * The caller needs to hold the page table lock and has to have the page table
+ * entries cleared/invalidated.
+ *
+ * This is similar to folio_try_dup_anon_rmap_pte(), however, not used during
+ * fork() to duplicate mappings, but instead to prepare for KSM or temporarily
+ * unmapping parts of a folio (swap, migration) via folio_remove_rmap_pte().
+ *
+ * Marking the mapped page shared can only fail if the folio maybe pinned;
+ * device private folios cannot get pinned and consequently this function cannot
+ * fail.
+ *
+ * Returns 0 if marking the mapped page possibly shared succeeded. Returns
+ * -EBUSY otherwise.
+ */
+static inline int folio_try_share_anon_rmap_pte(struct folio *folio,
+ struct page *page)
+{
+ return __folio_try_share_anon_rmap(folio, page, 1, RMAP_MODE_PTE);
+}
+
+/**
+ * folio_try_share_anon_rmap_pmd - try marking an exclusive anonymous page
+ * range mapped by a PMD possibly shared to
+ * prepare for temporary unmapping
+ * @folio: The folio to share the mapping of
+ * @page: The first page to share the mapping of
+ *
+ * The page range of the folio is defined by [page, page + HPAGE_PMD_NR)
+ *
+ * The caller needs to hold the page table lock and has to have the page table
+ * entries cleared/invalidated.
+ *
+ * This is similar to folio_try_dup_anon_rmap_pmd(), however, not used during
+ * fork() to duplicate a mapping, but instead to prepare for temporarily
+ * unmapping parts of a folio (swap, migration) via folio_remove_rmap_pmd().
+ *
+ * Marking the mapped pages shared can only fail if the folio maybe pinned;
+ * device private folios cannot get pinned and consequently this function cannot
+ * fail.
+ *
+ * Returns 0 if marking the mapped pages possibly shared succeeded. Returns
+ * -EBUSY otherwise.
+ */
+static inline int folio_try_share_anon_rmap_pmd(struct folio *folio,
+ struct page *page)
+{
+#ifdef CONFIG_TRANSPARENT_HUGEPAGE
+ return __folio_try_share_anon_rmap(folio, page, HPAGE_PMD_NR,
+ RMAP_MODE_PMD);
+#else
+ WARN_ON_ONCE(true);
+ return -EBUSY;
+#endif
+}
+
/*
* Called from mm/vmscan.c to handle paging out
*/
diff --git a/mm/gup.c b/mm/gup.c
index 0a5f0e91bfec..df83182ec72d 100644
--- a/mm/gup.c
+++ b/mm/gup.c
@@ -177,7 +177,7 @@ struct folio *try_grab_folio(struct page *page, int refs, unsigned int flags)
/*
* Adjust the pincount before re-checking the PTE for changes.
* This is essentially a smp_mb() and is paired with a memory
- * barrier in page_try_share_anon_rmap().
+ * barrier in folio_try_share_anon_rmap_*().
*/
smp_mb__after_atomic();

diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index 34f878916621..c681296fa429 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -2523,10 +2523,11 @@ static void __split_huge_pmd_locked(struct vm_area_struct *vma, pmd_t *pmd,
* In case we cannot clear PageAnonExclusive(), split the PMD
* only and let try_to_migrate_one() fail later.
*
- * See page_try_share_anon_rmap(): invalidate PMD first.
+ * See folio_try_share_anon_rmap_pmd(): invalidate PMD first.
*/
anon_exclusive = PageAnonExclusive(page);
- if (freeze && anon_exclusive && page_try_share_anon_rmap(page))
+ if (freeze && anon_exclusive &&
+ folio_try_share_anon_rmap_pmd(folio, page))
freeze = false;
if (!freeze) {
rmap_t rmap_flags = RMAP_NONE;
@@ -3554,9 +3555,9 @@ int set_pmd_migration_entry(struct page_vma_mapped_walk *pvmw,
flush_cache_range(vma, address, address + HPAGE_PMD_SIZE);
pmdval = pmdp_invalidate(vma, address, pvmw->pmd);

- /* See page_try_share_anon_rmap(): invalidate PMD first. */
+ /* See folio_try_share_anon_rmap_pmd(): invalidate PMD first. */
anon_exclusive = folio_test_anon(folio) && PageAnonExclusive(page);
- if (anon_exclusive && page_try_share_anon_rmap(page)) {
+ if (anon_exclusive && folio_try_share_anon_rmap_pmd(folio, page)) {
set_pmd_at(mm, address, pvmw->pmd, pmdval);
return -EBUSY;
}
diff --git a/mm/internal.h b/mm/internal.h
index a94355e70bd7..29589bc3f046 100644
--- a/mm/internal.h
+++ b/mm/internal.h
@@ -1047,7 +1047,7 @@ enum {
* * Ordinary GUP: Using the PT lock
* * GUP-fast and fork(): mm->write_protect_seq
* * GUP-fast and KSM or temporary unmapping (swap, migration): see
- * page_try_share_anon_rmap()
+ * folio_try_share_anon_rmap_*()
*
* Must be called with the (sub)page that's actually referenced via the
* page table entry, which might not necessarily be the head page for a
@@ -1090,7 +1090,7 @@ static inline bool gup_must_unshare(struct vm_area_struct *vma,
return is_cow_mapping(vma->vm_flags);
}

- /* Paired with a memory barrier in page_try_share_anon_rmap(). */
+ /* Paired with a memory barrier in folio_try_share_anon_rmap_*(). */
if (IS_ENABLED(CONFIG_HAVE_FAST_GUP))
smp_rmb();

diff --git a/mm/ksm.c b/mm/ksm.c
index b3d0cfaa2533..be76e9dabf4f 100644
--- a/mm/ksm.c
+++ b/mm/ksm.c
@@ -1161,8 +1161,9 @@ static int write_protect_page(struct vm_area_struct *vma, struct page *page,
goto out_unlock;
}

- /* See page_try_share_anon_rmap(): clear PTE first. */
- if (anon_exclusive && page_try_share_anon_rmap(page)) {
+ /* See folio_try_share_anon_rmap_pte(): clear PTE first. */
+ if (anon_exclusive &&
+ folio_try_share_anon_rmap_pte(page_folio(page), page)) {
set_pte_at(mm, pvmw.address, pvmw.pte, entry);
goto out_unlock;
}
diff --git a/mm/migrate_device.c b/mm/migrate_device.c
index c51c99151ebb..9d0c1ad73722 100644
--- a/mm/migrate_device.c
+++ b/mm/migrate_device.c
@@ -202,7 +202,7 @@ static int migrate_vma_collect_pmd(pmd_t *pmdp,
if (anon_exclusive) {
pte = ptep_clear_flush(vma, addr, ptep);

- if (page_try_share_anon_rmap(page)) {
+ if (folio_try_share_anon_rmap_pte(folio, page)) {
set_pte_at(mm, addr, ptep, pte);
folio_unlock(folio);
folio_put(folio);
diff --git a/mm/rmap.c b/mm/rmap.c
index b08dd7d6779d..45296739236f 100644
--- a/mm/rmap.c
+++ b/mm/rmap.c
@@ -1868,9 +1868,9 @@ static bool try_to_unmap_one(struct folio *folio, struct vm_area_struct *vma,
break;
}

- /* See page_try_share_anon_rmap(): clear PTE first. */
+ /* See folio_try_share_anon_rmap(): clear PTE first. */
if (anon_exclusive &&
- page_try_share_anon_rmap(subpage)) {
+ folio_try_share_anon_rmap_pte(folio, subpage)) {
swap_free(entry);
set_pte_at(mm, address, pvmw.pte, pteval);
ret = false;
@@ -2144,7 +2144,8 @@ static bool try_to_migrate_one(struct folio *folio, struct vm_area_struct *vma,
pte_t swp_pte;

if (anon_exclusive)
- BUG_ON(page_try_share_anon_rmap(subpage));
+ WARN_ON_ONCE(folio_try_share_anon_rmap_pte(folio,
+ subpage));

/*
* Store the pfn of the page in a special migration
@@ -2215,7 +2216,7 @@ static bool try_to_migrate_one(struct folio *folio, struct vm_area_struct *vma,
VM_BUG_ON_PAGE(pte_write(pteval) && folio_test_anon(folio) &&
!anon_exclusive, subpage);

- /* See page_try_share_anon_rmap(): clear PTE first. */
+ /* See folio_try_share_anon_rmap_pte(): clear PTE first. */
if (folio_test_hugetlb(folio)) {
if (anon_exclusive &&
hugetlb_try_share_anon_rmap(folio)) {
@@ -2226,7 +2227,7 @@ static bool try_to_migrate_one(struct folio *folio, struct vm_area_struct *vma,
break;
}
} else if (anon_exclusive &&
- page_try_share_anon_rmap(subpage)) {
+ folio_try_share_anon_rmap_pte(folio, subpage)) {
set_pte_at(mm, address, pvmw.pte, pteval);
ret = false;
page_vma_mapped_walk_done(&pvmw);
--
2.43.0