[PATCH v12 14/69] kernel/fork: use maple tree for dup_mmap() during forking

Liam Howlett liam.howlett at oracle.com
Tue Jul 19 19:17:48 PDT 2022

From: "Liam R. Howlett" <Liam.Howlett at Oracle.com>

The maple tree was already tracking VMAs in this function by an earlier
commit, but the rbtree iterator was being used to iterate the list.
Change the iterator to use a maple tree native iterator and switch to the
maple tree advanced API to avoid multiple walks of the tree during insert
operations.  Unexport the now-unused vma_store() function.

For performance reasons we bulk allocate the maple tree nodes.  The node
calculations are done internally to the tree and use the VMA count and
assume the worst-case node requirements.  The VM_DONT_COPY flag does not
allow for the most efficient copy method of the tree and so a bulk loading
algorithm is used.

Link: https://lkml.kernel.org/r/20220504010716.661115-16-Liam.Howlett@oracle.com
Link: https://lkml.kernel.org/r/20220621204632.3370049-15-Liam.Howlett@oracle.com
Signed-off-by: Liam R. Howlett <Liam.Howlett at Oracle.com>
Signed-off-by: Matthew Wilcox (Oracle) <willy at infradead.org>
Acked-by: Vlastimil Babka <vbabka at suse.cz>
Cc: Catalin Marinas <catalin.marinas at arm.com>
Cc: David Howells <dhowells at redhat.com>
Cc: SeongJae Park <sj at kernel.org>
Cc: Will Deacon <will at kernel.org>
Cc: Davidlohr Bueso <dave at stgolabs.net>
Signed-off-by: Andrew Morton <akpm at linux-foundation.org>
 include/linux/mm.h |  2 --
 kernel/fork.c      | 10 ++++++++--
 2 files changed, 8 insertions(+), 4 deletions(-)

diff --git a/include/linux/mm.h b/include/linux/mm.h
index dee609fe5c1f..60045508a518 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -2613,8 +2613,6 @@ extern bool arch_has_descending_max_zone_pfns(void);
 /* nommu.c */
 extern atomic_long_t mmap_pages_allocated;
 extern int nommu_shrink_inode_mappings(struct inode *, size_t, size_t);
-/* mmap.c */
-void vma_mas_store(struct vm_area_struct *vma, struct ma_state *mas);
 /* interval_tree.c */
 void vma_interval_tree_insert(struct vm_area_struct *node,
diff --git a/kernel/fork.c b/kernel/fork.c
index 1840da0732f6..f575a3bead0e 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -583,8 +583,9 @@ static __latent_entropy int dup_mmap(struct mm_struct *mm,
 	struct vm_area_struct *mpnt, *tmp, *prev, **pprev;
 	struct rb_node **rb_link, *rb_parent;
 	int retval;
-	unsigned long charge;
+	unsigned long charge = 0;
+	MA_STATE(old_mas, &oldmm->mm_mt, 0, 0);
 	MA_STATE(mas, &mm->mm_mt, 0, 0);
@@ -620,7 +621,12 @@ static __latent_entropy int dup_mmap(struct mm_struct *mm,
 		goto out;
 	prev = NULL;
-	for (mpnt = oldmm->mmap; mpnt; mpnt = mpnt->vm_next) {
+	retval = mas_expected_entries(&mas, oldmm->map_count);
+	if (retval)
+		goto out;
+	mas_for_each(&old_mas, mpnt, ULONG_MAX) {
 		struct file *file;
 		if (mpnt->vm_flags & VM_DONTCOPY) {

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