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 | 145 +++++++++++++++++++++++++++++--------------
 2 files changed, 100 insertions(+), 51 deletions(-)

diff --git a/include/linux/mm.h b/include/linux/mm.h
index 24c1c7c5a99c0..f7565b35ae931 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -1964,12 +1964,6 @@ 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 21d72cc602adc..84439f7720c62 100644
--- a/include/linux/rmap.h
+++ b/include/linux/rmap.h
@@ -354,68 +354,123 @@ static inline void folio_dup_file_rmap_pmd(struct folio *folio,
 #endif
 }
 
-static inline void __page_dup_rmap(struct page *page, bool compound)
+static inline int __folio_try_dup_anon_rmap(struct folio *folio,
+		struct page *page, unsigned int nr_pages,
+		struct vm_area_struct *src_vma, enum rmap_mode mode)
 {
-	VM_WARN_ON(folio_test_hugetlb(page_folio(page)));
+	int i;
 
-	if (compound) {
-		struct folio *folio = (struct folio *)page;
+	VM_WARN_ON_FOLIO(!folio_test_anon(folio), folio);
 
-		VM_BUG_ON_PAGE(compound && !PageHead(page), page);
-		atomic_inc(&folio->_entire_mapcount);
-	} else {
-		atomic_inc(&page->_mapcount);
+	/*
+	 * No need to check+clear for already shared PTEs/PMDs of the folio.
+	 * This includes PTE mappings of (order-0) KSM folios.
+	 */
+	if (likely(mode == RMAP_MODE_PTE)) {
+		for (i = 0; i < nr_pages; i++) {
+			if (PageAnonExclusive(page + i))
+				goto clear;
+		}
+	} else if (mode == RMAP_MODE_PMD) {
+		if (PageAnonExclusive(page))
+			goto clear;
 	}
+	goto dup;
+
+clear:
+	/*
+	 * 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.
+	 */
+	if (likely(!folio_is_device_private(folio) &&
+	    unlikely(folio_needs_cow_for_dma(src_vma, folio))))
+		return -EBUSY;
+
+	if (likely(mode == RMAP_MODE_PTE)) {
+		for (i = 0; i < nr_pages; i++)
+			ClearPageAnonExclusive(page + i);
+	} else if (mode == RMAP_MODE_PMD) {
+		ClearPageAnonExclusive(page);
+	}
+
+dup:
+	__folio_dup_rmap(folio, page, nr_pages, mode);
+	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 caller needs to hold the PT lock and the vma->vma_mm->write_protect_seq.
+ * The page range of the folio is defined by [page, page + nr_pages)
  *
- * Duplicating the mapping can only fail if the page may be pinned; device
- * private pages cannot get pinned and consequently this function cannot fail.
+ * The caller needs to hold the page table lock and the
+ * vma->vma_mm->write_protect_seq.
+ *
+ * Duplicating the mappings can only fail if the folio may be pinned; device
+ * private folios cannot get pinned and consequently this function cannot fail.
+ *
+ * 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.
+ *
+ * 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, unsigned 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.
  *
- * 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.
+ * Duplicating the mapping can only fail if the folio may be pinned; device
+ * private folios cannot get pinned and consequently this function cannot fail.
+ *
+ * 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.
  *
  * 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);
+#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;
-
-	/*
-	 * 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;
+	struct folio *folio = page_folio(page);
 
-	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);
 }
 
 /**
-- 
2.41.0

On 04.12.23 15:21, David Hildenbrand wrote:
> 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>
> ---

This is what I currently have (- any renaming):


 From 89c3180d6bbbf2236329b405b11e6a8a3cc2c088 Mon Sep 17 00:00:00 2001
From: David Hildenbrand <david@redhat.com>
Date: Thu, 30 Nov 2023 10:15:17 +0100
Subject: [PATCH] mm/rmap: introduce folio_try_dup_anon_rmap_[pte|ptes|pmd]()

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 | 143 ++++++++++++++++++++++++++++++-------------
  2 files changed, 99 insertions(+), 50 deletions(-)

diff --git a/include/linux/mm.h b/include/linux/mm.h
index 24c1c7c5a99c0..f7565b35ae931 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -1964,12 +1964,6 @@ 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 06951909bb39b..98862ab7347f2 100644
--- a/include/linux/rmap.h
+++ b/include/linux/rmap.h
@@ -354,68 +354,123 @@ static inline void folio_dup_file_rmap_pmd(struct folio *folio,
  #endif
  }
  
-static inline void __page_dup_rmap(struct page *page, bool compound)
+static inline int __folio_try_dup_anon_rmap(struct folio *folio,
+		struct page *page, unsigned 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.
+	 */
+	if (likely(mode == 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);
+	} else if (mode == RMAP_MODE_PMD) {
+		if (PageAnonExclusive(page)) {
+			if (unlikely(maybe_pinned))
+				return -EBUSY;
+			ClearPageAnonExclusive(page);
+		}
  		atomic_inc(&folio->_entire_mapcount);
-	} else {
-		atomic_inc(&page->_mapcount);
  	}
+	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 caller needs to hold the PT lock and the vma->vma_mm->write_protect_seq.
+ * The page range of the folio is defined by [page, page + nr_pages)
   *
- * Duplicating the mapping can only fail if the page may be pinned; device
- * private pages cannot get pinned and consequently this function cannot fail.
+ * The caller needs to hold the page table lock and the
+ * vma->vma_mm->write_protect_seq.
+ *
+ * Duplicating the mappings can only fail if the folio may be pinned; device
+ * private folios cannot get pinned and consequently this function cannot fail.
+ *
+ * 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.
+ *
+ * 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, unsigned 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.
   *
- * 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 mapping succeeds, the duplicated PMD has to be R/O in
+ * the parent and the child. They must *not* be writable after this call.
   *
   * 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);
+#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);
  }
  
  /**
-- 
2.41.0


-- 
Cheers,

David / dhildenb

On 04/12/2023 14:21, David Hildenbrand wrote:
> 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 | 145 +++++++++++++++++++++++++++++--------------
>  2 files changed, 100 insertions(+), 51 deletions(-)
> 
> diff --git a/include/linux/mm.h b/include/linux/mm.h
> index 24c1c7c5a99c0..f7565b35ae931 100644
> --- a/include/linux/mm.h
> +++ b/include/linux/mm.h
> @@ -1964,12 +1964,6 @@ 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 21d72cc602adc..84439f7720c62 100644
> --- a/include/linux/rmap.h
> +++ b/include/linux/rmap.h
> @@ -354,68 +354,123 @@ static inline void folio_dup_file_rmap_pmd(struct folio *folio,
>  #endif
>  }
>  
> -static inline void __page_dup_rmap(struct page *page, bool compound)
> +static inline int __folio_try_dup_anon_rmap(struct folio *folio,

__always_inline?

> +		struct page *page, unsigned int nr_pages,
> +		struct vm_area_struct *src_vma, enum rmap_mode mode)
>  {
> -	VM_WARN_ON(folio_test_hugetlb(page_folio(page)));
> +	int i;
>  
> -	if (compound) {
> -		struct folio *folio = (struct folio *)page;
> +	VM_WARN_ON_FOLIO(!folio_test_anon(folio), folio);
>  
> -		VM_BUG_ON_PAGE(compound && !PageHead(page), page);
> -		atomic_inc(&folio->_entire_mapcount);
> -	} else {
> -		atomic_inc(&page->_mapcount);
> +	/*
> +	 * No need to check+clear for already shared PTEs/PMDs of the folio.
> +	 * This includes PTE mappings of (order-0) KSM folios.
> +	 */
> +	if (likely(mode == RMAP_MODE_PTE)) {

Presumbly if __always_inline then the compiler will remove this if/else and just
keep the part indicated by mode? In which case "likely" is pretty useless? Same
for all similar sites in the other patches.

> +		for (i = 0; i < nr_pages; i++) {
> +			if (PageAnonExclusive(page + i))
> +				goto clear;
> +		}
> +	} else if (mode == RMAP_MODE_PMD) {
> +		if (PageAnonExclusive(page))
> +			goto clear;
>  	}
> +	goto dup;
> +
> +clear:
> +	/*
> +	 * 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.
> +	 */
> +	if (likely(!folio_is_device_private(folio) &&
> +	    unlikely(folio_needs_cow_for_dma(src_vma, folio))))
> +		return -EBUSY;
> +
> +	if (likely(mode == RMAP_MODE_PTE)) {
> +		for (i = 0; i < nr_pages; i++)

Do you really need to reset i=0 here? You have already checked that lower pages
are shared in the above loop, so can't you just start from the first exclusive
page here?

> +			ClearPageAnonExclusive(page + i);
> +	} else if (mode == RMAP_MODE_PMD) {
> +		ClearPageAnonExclusive(page);
> +	}
> +
> +dup:
> +	__folio_dup_rmap(folio, page, nr_pages, mode);
> +	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 caller needs to hold the PT lock and the vma->vma_mm->write_protect_seq.
> + * The page range of the folio is defined by [page, page + nr_pages)
>   *
> - * Duplicating the mapping can only fail if the page may be pinned; device
> - * private pages cannot get pinned and consequently this function cannot fail.
> + * The caller needs to hold the page table lock and the
> + * vma->vma_mm->write_protect_seq.
> + *
> + * Duplicating the mappings can only fail if the folio may be pinned; device
> + * private folios cannot get pinned and consequently this function cannot fail.
> + *
> + * 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.
> + *
> + * 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, unsigned 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.
>   *
> - * 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.
> + * Duplicating the mapping can only fail if the folio may be pinned; device
> + * private folios cannot get pinned and consequently this function cannot fail.
> + *
> + * 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.
>   *
>   * 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);
> +#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;
> -
> -	/*
> -	 * 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;
> +	struct folio *folio = page_folio(page);
>  
> -	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);
>  }
>  
>  /**

On 05.12.23 14:12, Ryan Roberts wrote:
> On 04/12/2023 14:21, David Hildenbrand wrote:
>> 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 | 145 +++++++++++++++++++++++++++++--------------
>>   2 files changed, 100 insertions(+), 51 deletions(-)
>>
>> diff --git a/include/linux/mm.h b/include/linux/mm.h
>> index 24c1c7c5a99c0..f7565b35ae931 100644
>> --- a/include/linux/mm.h
>> +++ b/include/linux/mm.h
>> @@ -1964,12 +1964,6 @@ 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 21d72cc602adc..84439f7720c62 100644
>> --- a/include/linux/rmap.h
>> +++ b/include/linux/rmap.h
>> @@ -354,68 +354,123 @@ static inline void folio_dup_file_rmap_pmd(struct folio *folio,
>>   #endif
>>   }
>>   
>> -static inline void __page_dup_rmap(struct page *page, bool compound)
>> +static inline int __folio_try_dup_anon_rmap(struct folio *folio,
> 
> __always_inline?

Yes.

> 
>> +		struct page *page, unsigned int nr_pages,
>> +		struct vm_area_struct *src_vma, enum rmap_mode mode)
>>   {
>> -	VM_WARN_ON(folio_test_hugetlb(page_folio(page)));
>> +	int i;
>>   
>> -	if (compound) {
>> -		struct folio *folio = (struct folio *)page;
>> +	VM_WARN_ON_FOLIO(!folio_test_anon(folio), folio);
>>   
>> -		VM_BUG_ON_PAGE(compound && !PageHead(page), page);
>> -		atomic_inc(&folio->_entire_mapcount);
>> -	} else {
>> -		atomic_inc(&page->_mapcount);
>> +	/*
>> +	 * No need to check+clear for already shared PTEs/PMDs of the folio.
>> +	 * This includes PTE mappings of (order-0) KSM folios.
>> +	 */
>> +	if (likely(mode == RMAP_MODE_PTE)) {
> 
> Presumbly if __always_inline then the compiler will remove this if/else and just
> keep the part indicated by mode? In which case "likely" is pretty useless? Same
> for all similar sites in the other patches.

Yes, also had this in mind. As long as we use __always_inline it 
shouldn't ever matter.

> 
>> +		for (i = 0; i < nr_pages; i++) {
>> +			if (PageAnonExclusive(page + i))
>> +				goto clear;
>> +		}
>> +	} else if (mode == RMAP_MODE_PMD) {
>> +		if (PageAnonExclusive(page))
>> +			goto clear;
>>   	}
>> +	goto dup;
>> +
>> +clear:
>> +	/*
>> +	 * 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.
>> +	 */
>> +	if (likely(!folio_is_device_private(folio) &&
>> +	    unlikely(folio_needs_cow_for_dma(src_vma, folio))))
>> +		return -EBUSY;
>> +
>> +	if (likely(mode == RMAP_MODE_PTE)) {
>> +		for (i = 0; i < nr_pages; i++)
> 
> Do you really need to reset i=0 here? You have already checked that lower pages
> are shared in the above loop, so can't you just start from the first exclusive
> page here?

It's best to check the updated patch I sent.

-- 
Cheers,

David / dhildenb

On 05.12.23 14:17, David Hildenbrand wrote:
> On 05.12.23 14:12, Ryan Roberts wrote:
>> On 04/12/2023 14:21, David Hildenbrand wrote:
>>> 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 | 145 +++++++++++++++++++++++++++++--------------
>>>    2 files changed, 100 insertions(+), 51 deletions(-)
>>>
>>> diff --git a/include/linux/mm.h b/include/linux/mm.h
>>> index 24c1c7c5a99c0..f7565b35ae931 100644
>>> --- a/include/linux/mm.h
>>> +++ b/include/linux/mm.h
>>> @@ -1964,12 +1964,6 @@ 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 21d72cc602adc..84439f7720c62 100644
>>> --- a/include/linux/rmap.h
>>> +++ b/include/linux/rmap.h
>>> @@ -354,68 +354,123 @@ static inline void folio_dup_file_rmap_pmd(struct folio *folio,
>>>    #endif
>>>    }
>>>    
>>> -static inline void __page_dup_rmap(struct page *page, bool compound)
>>> +static inline int __folio_try_dup_anon_rmap(struct folio *folio,
>>
>> __always_inline?
> 
> Yes.
> 
>>
>>> +		struct page *page, unsigned int nr_pages,
>>> +		struct vm_area_struct *src_vma, enum rmap_mode mode)
>>>    {
>>> -	VM_WARN_ON(folio_test_hugetlb(page_folio(page)));
>>> +	int i;
>>>    
>>> -	if (compound) {
>>> -		struct folio *folio = (struct folio *)page;
>>> +	VM_WARN_ON_FOLIO(!folio_test_anon(folio), folio);
>>>    
>>> -		VM_BUG_ON_PAGE(compound && !PageHead(page), page);
>>> -		atomic_inc(&folio->_entire_mapcount);
>>> -	} else {
>>> -		atomic_inc(&page->_mapcount);
>>> +	/*
>>> +	 * No need to check+clear for already shared PTEs/PMDs of the folio.
>>> +	 * This includes PTE mappings of (order-0) KSM folios.
>>> +	 */
>>> +	if (likely(mode == RMAP_MODE_PTE)) {
>>
>> Presumbly if __always_inline then the compiler will remove this if/else and just
>> keep the part indicated by mode? In which case "likely" is pretty useless? Same
>> for all similar sites in the other patches.
> 
> Yes, also had this in mind. As long as we use __always_inline it
> shouldn't ever matter.

It seems to be cleanest to just do:

switch (mode) {
case RMAP_MODE_PTE:
	...
	break;
case RMAP_MODE_PMD:
	...
	break;
}

-- 
Cheers,

David / dhildenb

On 05/12/2023 13:32, David Hildenbrand wrote:
> On 05.12.23 14:17, David Hildenbrand wrote:
>> On 05.12.23 14:12, Ryan Roberts wrote:
>>> On 04/12/2023 14:21, David Hildenbrand wrote:
>>>> 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 | 145 +++++++++++++++++++++++++++++--------------
>>>>    2 files changed, 100 insertions(+), 51 deletions(-)
>>>>
>>>> diff --git a/include/linux/mm.h b/include/linux/mm.h
>>>> index 24c1c7c5a99c0..f7565b35ae931 100644
>>>> --- a/include/linux/mm.h
>>>> +++ b/include/linux/mm.h
>>>> @@ -1964,12 +1964,6 @@ 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 21d72cc602adc..84439f7720c62 100644
>>>> --- a/include/linux/rmap.h
>>>> +++ b/include/linux/rmap.h
>>>> @@ -354,68 +354,123 @@ static inline void folio_dup_file_rmap_pmd(struct
>>>> folio *folio,
>>>>    #endif
>>>>    }
>>>>    -static inline void __page_dup_rmap(struct page *page, bool compound)
>>>> +static inline int __folio_try_dup_anon_rmap(struct folio *folio,
>>>
>>> __always_inline?
>>
>> Yes.
>>
>>>
>>>> +        struct page *page, unsigned int nr_pages,
>>>> +        struct vm_area_struct *src_vma, enum rmap_mode mode)
>>>>    {
>>>> -    VM_WARN_ON(folio_test_hugetlb(page_folio(page)));
>>>> +    int i;
>>>>    -    if (compound) {
>>>> -        struct folio *folio = (struct folio *)page;
>>>> +    VM_WARN_ON_FOLIO(!folio_test_anon(folio), folio);
>>>>    -        VM_BUG_ON_PAGE(compound && !PageHead(page), page);
>>>> -        atomic_inc(&folio->_entire_mapcount);
>>>> -    } else {
>>>> -        atomic_inc(&page->_mapcount);
>>>> +    /*
>>>> +     * No need to check+clear for already shared PTEs/PMDs of the folio.
>>>> +     * This includes PTE mappings of (order-0) KSM folios.
>>>> +     */
>>>> +    if (likely(mode == RMAP_MODE_PTE)) {
>>>
>>> Presumbly if __always_inline then the compiler will remove this if/else and just
>>> keep the part indicated by mode? In which case "likely" is pretty useless? Same
>>> for all similar sites in the other patches.
>>
>> Yes, also had this in mind. As long as we use __always_inline it
>> shouldn't ever matter.
> 
> It seems to be cleanest to just do:
> 
> switch (mode) {
> case RMAP_MODE_PTE:
>     ...
>     break;
> case RMAP_MODE_PMD:
>     ...
>     break;
> }
> 

Agreed.

> -static inline void __page_dup_rmap(struct page *page, bool compound)
> +static inline int __folio_try_dup_anon_rmap(struct folio *folio,
> +		struct page *page, unsigned int nr_pages,
> +		struct vm_area_struct *src_vma, enum rmap_mode mode)
>   {
> -	VM_WARN_ON(folio_test_hugetlb(page_folio(page)));
> +	int i;
>   
> -	if (compound) {
> -		struct folio *folio = (struct folio *)page;
> +	VM_WARN_ON_FOLIO(!folio_test_anon(folio), folio);
>   
> -		VM_BUG_ON_PAGE(compound && !PageHead(page), page);
> -		atomic_inc(&folio->_entire_mapcount);
> -	} else {
> -		atomic_inc(&page->_mapcount);
> +	/*
> +	 * No need to check+clear for already shared PTEs/PMDs of the folio.
> +	 * This includes PTE mappings of (order-0) KSM folios.
> +	 */
> +	if (likely(mode == RMAP_MODE_PTE)) {
> +		for (i = 0; i < nr_pages; i++) {
> +			if (PageAnonExclusive(page + i))
> +				goto clear;
> +		}
> +	} else if (mode == RMAP_MODE_PMD) {
> +		if (PageAnonExclusive(page))
> +			goto clear;
>   	}
> +	goto dup;
> +
> +clear:
> +	/*
> +	 * 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.
> +	 */
> +	if (likely(!folio_is_device_private(folio) &&
> +	    unlikely(folio_needs_cow_for_dma(src_vma, folio))))
> +		return -EBUSY;
> +
> +	if (likely(mode == RMAP_MODE_PTE)) {
> +		for (i = 0; i < nr_pages; i++)
> +			ClearPageAnonExclusive(page + i);
> +	} else if (mode == RMAP_MODE_PMD) {
> +		ClearPageAnonExclusive(page);
> +	}
> +
> +dup:
> +	__folio_dup_rmap(folio, page, nr_pages, mode);
> +	return 0;

Playing with this, I think it can be implemented more efficiently by 
only looping once and optimizing for the common case that PAE is set. 
Will have to do some more measurements.

-- 
Cheers,

David / dhildenb