[PATCH v13 14/70] kernel/fork: use maple tree for dup_mmap() during forking

Liam Howlett
2022-08-22T15:06:16Z

From: "Liam R. Howlett" <Liam.Howlett@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.

Signed-off-by: Liam R. Howlett <Liam.Howlett@Oracle.com>
Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
---
include/linux/mm.h | 2 --
kernel/fork.c | 15 +++++++++++++--
2 files changed, 13 insertions(+), 4 deletions(-)

diff --git a/include/linux/mm.h b/include/linux/mm.h
index 352f5d9f212c..d8230a8740a1 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -2591,8 +2591,6 @@ 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 273364207f17..16970c346b5b 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;
LIST_HEAD(uf);
+ MA_STATE(old_mas, &oldmm->mm_mt, 0, 0);
MA_STATE(mas, &mm->mm_mt, 0, 0);

uprobe_start_dup_mmap();
@@ -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) {
@@ -703,6 +709,8 @@ static __latent_entropy int dup_mmap(struct mm_struct *mm,
mas.index = tmp->vm_start;
mas.last = tmp->vm_end - 1;
mas_store(&mas, tmp);
+ if (mas_is_err(&mas))
+ goto fail_nomem_mas_store;

mm->map_count++;
if (!(tmp->vm_flags & VM_WIPEONFORK))
@@ -726,6 +734,9 @@ static __latent_entropy int dup_mmap(struct mm_struct *mm,
fail_uprobe_end:
uprobe_end_dup_mmap();
return retval;
+
+fail_nomem_mas_store:
+ unlink_anon_vmas(tmp);
fail_nomem_anon_vma_fork:
mpol_put(vma_policy(tmp));
fail_nomem_policy:
--
2.35.1