linux-kernel - [PATCH v14 14/70] kernel/fork: use maple tree for dup

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Date:   Tue, 6 Sep 2022 19:48:47 +0000
From:   Liam Howlett <liam.howlett@...cle.com>
To:     "maple-tree@...ts.infradead.org" <maple-tree@...ts.infradead.org>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Andrew Morton <akpm@...ux-foundation.org>
CC:     Liam Howlett <liam.howlett@...cle.com>,
        Matthew Wilcox <willy@...radead.org>,
        Vlastimil Babka <vbabka@...e.cz>
Subject: [PATCH v14 14/70] kernel/fork: use maple tree for dup_mmap() during
 forking

From: "Liam R. Howlett" <Liam.Howlett@...cle.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@...cle.com>
Signed-off-by: Matthew Wilcox (Oracle) <willy@...radead.org>
Acked-by: Vlastimil Babka <vbabka@...e.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 a458e5f73fee..fef2cbdb44bb 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -2603,8 +2603,6 @@ 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