[PATCH v1 34/39] mm/rmap: introduce folio_try_dup_anon_rmap_[pte|ptes|pmd]()

David Hildenbrand
2023-12-11T15:58:34Z

The last user of page_needs_cow_for_dma() and __page_dup_rmap() are gone,
remove them.

Add folio_try_dup_anon_rmap_ptes() right away, we want to perform rmap
baching during fork() soon.

Signed-off-by: David Hildenbrand <david@redhat.com>
---
include/linux/mm.h | 6 --
include/linux/rmap.h | 150 ++++++++++++++++++++++++++++++-------------
2 files changed, 106 insertions(+), 50 deletions(-)

diff --git a/include/linux/mm.h b/include/linux/mm.h
index ae547b62f325..30edf3f7d1f3 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -1975,12 +1975,6 @@ static inline bool folio_needs_cow_for_dma(struct vm_area_struct *vma,
return folio_maybe_dma_pinned(folio);
}

-static inline bool page_needs_cow_for_dma(struct vm_area_struct *vma,
- struct page *page)
-{
- return folio_needs_cow_for_dma(vma, page_folio(page));
-}
-
/**
* is_zero_page - Query if a page is a zero page
* @page: The page to query
diff --git a/include/linux/rmap.h b/include/linux/rmap.h
index df60e44fecad..c6d8a02ecd56 100644
--- a/include/linux/rmap.h
+++ b/include/linux/rmap.h
@@ -365,68 +365,130 @@ static inline void folio_dup_file_rmap_pmd(struct folio *folio,
#endif
}

-static inline void __page_dup_rmap(struct page *page, bool compound)
+static __always_inline int __folio_try_dup_anon_rmap(struct folio *folio,
+ struct page *page, int nr_pages, struct vm_area_struct *src_vma,
+ enum rmap_mode mode)
{
- VM_WARN_ON(folio_test_hugetlb(page_folio(page)));
+ bool maybe_pinned;
+ int i;

- if (compound) {
- struct folio *folio = (struct folio *)page;
+ VM_WARN_ON_FOLIO(!folio_test_anon(folio), folio);
+ __folio_rmap_sanity_checks(folio, page, nr_pages, mode);

- VM_BUG_ON_PAGE(compound && !PageHead(page), page);
+ /*
+ * If this folio may have been pinned by the parent process,
+ * don't allow to duplicate the mappings but instead require to e.g.,
+ * copy the subpage immediately for the child so that we'll always
+ * guarantee the pinned folio won't be randomly replaced in the
+ * future on write faults.
+ */
+ maybe_pinned = likely(!folio_is_device_private(folio)) &&
+ unlikely(folio_needs_cow_for_dma(src_vma, folio));
+
+ /*
+ * No need to check+clear for already shared PTEs/PMDs of the
+ * folio. But if any page is PageAnonExclusive, we must fallback to
+ * copying if the folio maybe pinned.
+ */
+ switch (mode) {
+ case RMAP_MODE_PTE:
+ if (unlikely(maybe_pinned)) {
+ for (i = 0; i < nr_pages; i++)
+ if (PageAnonExclusive(page + i))
+ return -EBUSY;
+ }
+ do {
+ if (PageAnonExclusive(page))
+ ClearPageAnonExclusive(page);
+ atomic_inc(&page->_mapcount);
+ } while (page++, --nr_pages > 0);
+ break;
+ case RMAP_MODE_PMD:
+ if (PageAnonExclusive(page)) {
+ if (unlikely(maybe_pinned))
+ return -EBUSY;
+ ClearPageAnonExclusive(page);
+ }
atomic_inc(&folio->_entire_mapcount);
- } else {
- atomic_inc(&page->_mapcount);
+ break;
}
+ return 0;
}

/**
- * page_try_dup_anon_rmap - try duplicating a mapping of an already mapped
- * anonymous page
- * @page: the page to duplicate the mapping for
- * @compound: the page is mapped as compound or as a small page
- * @vma: the source vma
+ * folio_try_dup_anon_rmap_ptes - try duplicating PTE mappings of a page range
+ * of a folio
+ * @folio: The folio to duplicate the mappings of
+ * @page: The first page to duplicate the mappings of
+ * @nr_pages: The number of pages of which the mapping will be duplicated
+ * @src_vma: The vm area from which the mappings are duplicated
+ *
+ * The page range of the folio is defined by [page, page + nr_pages)
*
- * The caller needs to hold the PT lock and the vma->vma_mm->write_protect_seq.
+ * The caller needs to hold the page table lock and the
+ * vma->vma_mm->write_protect_seq.
*
- * Duplicating the mapping can only fail if the page may be pinned; device
- * private pages cannot get pinned and consequently this function cannot fail.
+ * Duplicating the mappings can only fail if the folio may be pinned; device
+ * private folios cannot get pinned and consequently this function cannot fail
+ * for them.
*
- * If duplicating the mapping succeeds, the page has to be mapped R/O into
- * the parent and the child. It must *not* get mapped writable after this call.
+ * If duplicating the mappings succeeded, the duplicated PTEs have to be R/O in
+ * the parent and the child. They must *not* be writable after this call
+ * succeeded.
+ *
+ * Returns 0 if duplicating the mappings succeeded. Returns -EBUSY otherwise.
+ */
+static inline int folio_try_dup_anon_rmap_ptes(struct folio *folio,
+ struct page *page, int nr_pages, struct vm_area_struct *src_vma)
+{
+ return __folio_try_dup_anon_rmap(folio, page, nr_pages, src_vma,
+ RMAP_MODE_PTE);
+}
+#define folio_try_dup_anon_rmap_pte(folio, page, vma) \
+ folio_try_dup_anon_rmap_ptes(folio, page, 1, vma)
+
+/**
+ * folio_try_dup_anon_rmap_pmd - try duplicating a PMD mapping of a page range
+ * of a folio
+ * @folio: The folio to duplicate the mapping of
+ * @page: The first page to duplicate the mapping of
+ * @src_vma: The vm area from which the mapping is duplicated
+ *
+ * The page range of the folio is defined by [page, page + HPAGE_PMD_NR)
+ *
+ * The caller needs to hold the page table lock and the
+ * vma->vma_mm->write_protect_seq.
+ *
+ * Duplicating the mapping can only fail if the folio may be pinned; device
+ * private folios cannot get pinned and consequently this function cannot fail
+ * for them.
+ *
+ * If duplicating the mapping succeeds, the duplicated PMD has to be R/O in
+ * the parent and the child. They must *not* be writable after this call
+ * succeeded.
*
* Returns 0 if duplicating the mapping succeeded. Returns -EBUSY otherwise.
*/
+static inline int folio_try_dup_anon_rmap_pmd(struct folio *folio,
+ struct page *page, struct vm_area_struct *src_vma)
+{
+#ifdef CONFIG_TRANSPARENT_HUGEPAGE
+ return __folio_try_dup_anon_rmap(folio, page, HPAGE_PMD_NR, src_vma,
+ RMAP_MODE_PMD);
+#else
+ WARN_ON_ONCE(true);
+ return -EBUSY;
+#endif
+}
+
static inline int page_try_dup_anon_rmap(struct page *page, bool compound,
struct vm_area_struct *vma)
{
- VM_BUG_ON_PAGE(!PageAnon(page), page);
-
- /*
- * No need to check+clear for already shared pages, including KSM
- * pages.
- */
- if (!PageAnonExclusive(page))
- goto dup;
+ struct folio *folio = page_folio(page);

- /*
- * If this page may have been pinned by the parent process,
- * don't allow to duplicate the mapping but instead require to e.g.,
- * copy the page immediately for the child so that we'll always
- * guarantee the pinned page won't be randomly replaced in the
- * future on write faults.
- */
- if (likely(!is_device_private_page(page)) &&
- unlikely(page_needs_cow_for_dma(vma, page)))
- return -EBUSY;
-
- ClearPageAnonExclusive(page);
- /*
- * It's okay to share the anon page between both processes, mapping
- * the page R/O into both processes.
- */
-dup:
- __page_dup_rmap(page, compound);
- return 0;
+ if (likely(!compound))
+ return folio_try_dup_anon_rmap_pte(folio, page, vma);
+ return folio_try_dup_anon_rmap_pmd(folio, page, vma);
}

/**
--
2.43.0