Commit 61d90309 authored by David Hildenbrand's avatar David Hildenbrand Committed by Andrew Morton
Browse files

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.

Link: https://lkml.kernel.org/r/20231220224504.646757-35-david@redhat.com


Signed-off-by: default avatarDavid Hildenbrand <david@redhat.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Muchun Song <muchun.song@linux.dev>
Cc: Muchun Song <songmuchun@bytedance.com>
Cc: Peter Xu <peterx@redhat.com>
Cc: Ryan Roberts <ryan.roberts@arm.com>
Cc: Yin Fengwei <fengwei.yin@intel.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
parent d8ef5e31

include/linux/mm.h

+0 −6
Original line number Diff line number Diff line
@@ -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

include/linux/rmap.h

+106 −44
Original line number Diff line number Diff line
@@ -362,68 +362,130 @@ 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_level level)

{

	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, level);



		VM_BUG_ON_PAGE(compound && !PageHead(page), page);

		atomic_inc(&folio->_entire_mapcount);

	} else {

	/*

	 * 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 (level) {

	case RMAP_LEVEL_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_LEVEL_PMD:

		if (PageAnonExclusive(page)) {

			if (unlikely(maybe_pinned))

				return -EBUSY;

			ClearPageAnonExclusive(page);

		}

		atomic_inc(&folio->_entire_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 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.

 *

 * 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 mappings can only fail if the folio may be pinned; device

 * private folios cannot get pinned and consequently this function cannot fail

 * for them.

 *

 * Returns 0 if duplicating the mapping succeeded. Returns -EBUSY otherwise.

 * 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 page_try_dup_anon_rmap(struct page *page, bool compound,

					 struct vm_area_struct *vma)

static inline int folio_try_dup_anon_rmap_ptes(struct folio *folio,

		struct page *page, int nr_pages, struct vm_area_struct *src_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;

	return __folio_try_dup_anon_rmap(folio, page, nr_pages, src_vma,

					 RMAP_LEVEL_PTE);

}

#define folio_try_dup_anon_rmap_pte(folio, page, vma) \

	folio_try_dup_anon_rmap_ptes(folio, page, 1, vma)



	/*

	 * 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.

/**

 * 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.

 */

	if (likely(!is_device_private_page(page)) &&

	    unlikely(page_needs_cow_for_dma(vma, page)))

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_LEVEL_PMD);

#else

	WARN_ON_ONCE(true);

	return -EBUSY;

#endif

}



	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;

static inline int page_try_dup_anon_rmap(struct page *page, bool compound,

					 struct vm_area_struct *vma)

{

	struct folio *folio = page_folio(page);



	if (likely(!compound))

		return folio_try_dup_anon_rmap_pte(folio, page, vma);

	return folio_try_dup_anon_rmap_pmd(folio, page, vma);

}



/**