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

[Andrew Morton <akpm@linux-foundation.org>]

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

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------------------------------------------------------
From: David Hildenbrand <david@redhat.com>
Subject: mm/rmap: introduce and use hugetlb_try_share_anon_rmap()
Date: Wed, 20 Dec 2023 23:44:29 +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 try_to_unmap_one() does not need care.  Easy to spot because
among all that nasty hugetlb special-casing in that function, we're not
using set_huge_pte_at() on the anon path -- well, and that code assumes
that we would want to swapout.

Link: https://lkml.kernel.org/r/20231220224504.646757-6-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>
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>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 include/linux/rmap.h |   25 +++++++++++++++++++++++++
 mm/rmap.c            |   15 ++++++++++-----
 2 files changed, 35 insertions(+), 5 deletions(-)

--- a/include/linux/rmap.h~mm-rmap-introduce-and-use-hugetlb_try_share_anon_rmap
+++ a/include/linux/rmap.h
@@ -227,6 +227,30 @@ static inline int hugetlb_try_dup_anon_r
 	return 0;
 }
 
+/* See page_try_share_anon_rmap() */
+static inline int hugetlb_try_share_anon_rmap(struct folio *folio)
+{
+	VM_WARN_ON_FOLIO(!folio_test_hugetlb(folio), folio);
+	VM_WARN_ON_FOLIO(!folio_test_anon(folio), folio);
+	VM_WARN_ON_FOLIO(!PageAnonExclusive(&folio->page), folio);
+
+	/* Paired with the memory barrier in try_grab_folio(). */
+	if (IS_ENABLED(CONFIG_HAVE_FAST_GUP))
+		smp_mb();
+
+	if (unlikely(folio_maybe_dma_pinned(folio)))
+		return -EBUSY;
+	ClearPageAnonExclusive(&folio->page);
+
+	/*
+	 * This is conceptually a smp_wmb() paired with the smp_rmb() in
+	 * gup_must_unshare().
+	 */
+	if (IS_ENABLED(CONFIG_HAVE_FAST_GUP))
+		smp_mb__after_atomic();
+	return 0;
+}
+
 static inline void hugetlb_add_file_rmap(struct folio *folio)
 {
 	VM_WARN_ON_FOLIO(!folio_test_hugetlb(folio), folio);
@@ -331,6 +355,7 @@ dup:
  */
 static inline int page_try_share_anon_rmap(struct page *page)
 {
+	VM_WARN_ON(folio_test_hugetlb(page_folio(page)));
 	VM_BUG_ON_PAGE(!PageAnon(page) || !PageAnonExclusive(page), page);
 
 	/* device private pages cannot get pinned via GUP. */
--- a/mm/rmap.c~mm-rmap-introduce-and-use-hugetlb_try_share_anon_rmap
+++ a/mm/rmap.c
@@ -2149,13 +2149,18 @@ static bool try_to_migrate_one(struct fo
 				       !anon_exclusive, subpage);
 
 			/* See page_try_share_anon_rmap(): clear PTE first. */
-			if (anon_exclusive &&
-			    page_try_share_anon_rmap(subpage)) {
-				if (folio_test_hugetlb(folio))
+			if (folio_test_hugetlb(folio)) {
+				if (anon_exclusive &&
+				    hugetlb_try_share_anon_rmap(folio)) {
 					set_huge_pte_at(mm, address, pvmw.pte,
 							pteval, hsz);
-				else
-					set_pte_at(mm, address, pvmw.pte, pteval);
+					ret = false;
+					page_vma_mapped_walk_done(&pvmw);
+					break;
+				}
+			} else if (anon_exclusive &&
+				   page_try_share_anon_rmap(subpage)) {
+				set_pte_at(mm, address, pvmw.pte, pteval);
 				ret = false;
 				page_vma_mapped_walk_done(&pvmw);
 				break;
_

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