+ mm-rmap-introduce-and-use-hugetlb_try_dup_anon_rmap.patch added to mm-unstable branch

+ mm-rmap-introduce-and-use-hugetlb_try_dup_anon_rmap.patch added to mm-unstable branch

[Andrew Morton]

The patch titled
     Subject: mm/rmap: introduce and use hugetlb_try_dup_anon_rmap()
has been added to the -mm mm-unstable branch.  Its filename is
     mm-rmap-introduce-and-use-hugetlb_try_dup_anon_rmap.patch

This patch will shortly appear at
     https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-rmap-introduce-and-use-hugetlb_try_dup_anon_rmap.patch

This patch will later appear in the mm-unstable branch at
    git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

Before you just go and hit "reply", please:
   a) Consider who else should be cc'ed
   b) Prefer to cc a suitable mailing list as well
   c) Ideally: find the original patch on the mailing list and do a
      reply-to-all to that, adding suitable additional cc's

*** Remember to use Documentation/process/submit-checklist.rst when testing your code ***

The -mm tree is included into linux-next via the mm-everything
branch at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
and is updated there every 2-3 working days

------------------------------------------------------
From: David Hildenbrand <david@redhat.com>
Subject: mm/rmap: introduce and use hugetlb_try_dup_anon_rmap()
Date: Wed, 20 Dec 2023 23:44:28 +0100

hugetlb rmap handling differs quite a lot from "ordinary" rmap code.  For
example, hugetlb currently only supports entire mappings, and treats any
mapping as mapped using a single "logical PTE".  Let's move it out of the
way so we can overhaul our "ordinary" rmap.  implementation/interface.

So let's introduce and use hugetlb_try_dup_anon_rmap() to make all hugetlb
handling use dedicated hugetlb_* rmap functions.

Add sanity checks that we end up with the right folios in the right
functions.

Note that is_device_private_page() does not apply to hugetlb.

Link: https://lkml.kernel.org/r/20231220224504.646757-5-david@redhat.com
Signed-off-by: David Hildenbrand <david@redhat.com>
Reviewed-by: Yin Fengwei <fengwei.yin@intel.com>
Reviewed-by: Ryan Roberts <ryan.roberts@arm.com>
Reviewed-by: Muchun Song <songmuchun@bytedance.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Muchun Song <muchun.song@linux.dev>
Cc: Peter Xu <peterx@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 include/linux/mm.h   |   12 +++++++++---
 include/linux/rmap.h |   18 ++++++++++++++++++
 mm/hugetlb.c         |    3 +--
 3 files changed, 28 insertions(+), 5 deletions(-)

--- a/include/linux/mm.h~mm-rmap-introduce-and-use-hugetlb_try_dup_anon_rmap
+++ a/include/linux/mm.h
@@ -1964,15 +1964,21 @@ static inline bool page_maybe_dma_pinned
  *
  * The caller has to hold the PT lock and the vma->vm_mm->->write_protect_seq.
  */
-static inline bool page_needs_cow_for_dma(struct vm_area_struct *vma,
-					  struct page *page)
+static inline bool folio_needs_cow_for_dma(struct vm_area_struct *vma,
+					  struct folio *folio)
 {
 	VM_BUG_ON(!(raw_read_seqcount(&vma->vm_mm->write_protect_seq) & 1));
 
 	if (!test_bit(MMF_HAS_PINNED, &vma->vm_mm->flags))
 		return false;
 
-	return page_maybe_dma_pinned(page);
+	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));
 }
 
 /**
--- a/include/linux/rmap.h~mm-rmap-introduce-and-use-hugetlb_try_dup_anon_rmap
+++ a/include/linux/rmap.h
@@ -211,6 +211,22 @@ void hugetlb_add_anon_rmap(struct folio
 void hugetlb_add_new_anon_rmap(struct folio *, struct vm_area_struct *,
 		unsigned long address);
 
+/* See page_try_dup_anon_rmap() */
+static inline int hugetlb_try_dup_anon_rmap(struct folio *folio,
+		struct vm_area_struct *vma)
+{
+	VM_WARN_ON_FOLIO(!folio_test_hugetlb(folio), folio);
+	VM_WARN_ON_FOLIO(!folio_test_anon(folio), folio);
+
+	if (PageAnonExclusive(&folio->page)) {
+		if (unlikely(folio_needs_cow_for_dma(vma, folio)))
+			return -EBUSY;
+		ClearPageAnonExclusive(&folio->page);
+	}
+	atomic_inc(&folio->_entire_mapcount);
+	return 0;
+}
+
 static inline void hugetlb_add_file_rmap(struct folio *folio)
 {
 	VM_WARN_ON_FOLIO(!folio_test_hugetlb(folio), folio);
@@ -228,6 +244,8 @@ static inline void hugetlb_remove_rmap(s
 
 static inline void __page_dup_rmap(struct page *page, bool compound)
 {
+	VM_WARN_ON(folio_test_hugetlb(page_folio(page)));
+
 	if (compound) {
 		struct folio *folio = (struct folio *)page;
 
--- a/mm/hugetlb.c~mm-rmap-introduce-and-use-hugetlb_try_dup_anon_rmap
+++ a/mm/hugetlb.c
@@ -5409,8 +5409,7 @@ again:
 			 */
 			if (!folio_test_anon(pte_folio)) {
 				hugetlb_add_file_rmap(pte_folio);
-			} else if (page_try_dup_anon_rmap(&pte_folio->page,
-							  true, src_vma)) {
+			} else if (hugetlb_try_dup_anon_rmap(pte_folio, src_vma)) {
 				pte_t src_pte_old = entry;
 				struct folio *new_folio;
 
_

Patches currently in -mm which might be from david@redhat.com are

mm-rmap-rename-hugepage_add-to-hugetlb_add.patch
mm-rmap-introduce-and-use-hugetlb_remove_rmap.patch
mm-rmap-introduce-and-use-hugetlb_add_file_rmap.patch
mm-rmap-introduce-and-use-hugetlb_try_dup_anon_rmap.patch
mm-rmap-introduce-and-use-hugetlb_try_share_anon_rmap.patch
mm-rmap-add-hugetlb-sanity-checks-for-anon-rmap-handling.patch
mm-rmap-convert-folio_add_file_rmap_range-into-folio_add_file_rmap_.patch
mm-memory-page_add_file_rmap-folio_add_file_rmap_.patch
mm-huge_memory-page_add_file_rmap-folio_add_file_rmap_pmd.patch
mm-migrate-page_add_file_rmap-folio_add_file_rmap_pte.patch
mm-userfaultfd-page_add_file_rmap-folio_add_file_rmap_pte.patch
mm-rmap-remove-page_add_file_rmap.patch
mm-rmap-factor-out-adding-folio-mappings-into-__folio_add_rmap.patch
mm-rmap-introduce-folio_add_anon_rmap_.patch
mm-huge_memory-batch-rmap-operations-in-__split_huge_pmd_locked.patch
mm-huge_memory-page_add_anon_rmap-folio_add_anon_rmap_pmd.patch
mm-migrate-page_add_anon_rmap-folio_add_anon_rmap_pte.patch
mm-ksm-page_add_anon_rmap-folio_add_anon_rmap_pte.patch
mm-swapfile-page_add_anon_rmap-folio_add_anon_rmap_pte.patch
mm-memory-page_add_anon_rmap-folio_add_anon_rmap_pte.patch
mm-rmap-remove-page_add_anon_rmap.patch
mm-rmap-remove-rmap_compound.patch
mm-rmap-introduce-folio_remove_rmap_.patch
kernel-events-uprobes-page_remove_rmap-folio_remove_rmap_pte.patch
mm-huge_memory-page_remove_rmap-folio_remove_rmap_pmd.patch
mm-khugepaged-page_remove_rmap-folio_remove_rmap_pte.patch
mm-ksm-page_remove_rmap-folio_remove_rmap_pte.patch
mm-memory-page_remove_rmap-folio_remove_rmap_pte.patch
mm-migrate_device-page_remove_rmap-folio_remove_rmap_pte.patch
mm-rmap-page_remove_rmap-folio_remove_rmap_pte.patch
documentation-stop-referring-to-page_remove_rmap.patch
mm-rmap-remove-page_remove_rmap.patch
mm-rmap-convert-page_dup_file_rmap-to-folio_dup_file_rmap_.patch
mm-rmap-introduce-folio_try_dup_anon_rmap_.patch
mm-huge_memory-page_try_dup_anon_rmap-folio_try_dup_anon_rmap_pmd.patch
mm-memory-page_try_dup_anon_rmap-folio_try_dup_anon_rmap_pte.patch
mm-rmap-remove-page_try_dup_anon_rmap.patch
mm-convert-page_try_share_anon_rmap-to-folio_try_share_anon_rmap_.patch
mm-rmap-rename-compound_mapped-to-entirely_mapped.patch
mm-remove-one-last-reference-to-page_add__rmap.patch