[PATCH v13 65/70] nommu: remove uses of VMA linked list

Liam Howlett
2022-08-22T15:13:32Z

From: "Matthew Wilcox (Oracle)" <willy@infradead.org>

Use the maple tree or VMA iterator instead. This is faster and will allow
us to shrink the VMA.

Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Signed-off-by: Liam R. Howlett <Liam.Howlett@Oracle.com>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
---
mm/nommu.c | 135 +++++++++++++++++++++++++++++++++++++++--------------
1 file changed, 101 insertions(+), 34 deletions(-)

diff --git a/mm/nommu.c b/mm/nommu.c
index 265a444a2cc2..171faa07e577 100644
--- a/mm/nommu.c
+++ b/mm/nommu.c
@@ -557,26 +557,14 @@ void vma_mas_remove(struct vm_area_struct *vma, struct ma_state *mas)
mas_store_prealloc(mas, NULL);
}

-/*
- * add a VMA into a process's mm_struct in the appropriate place in the list
- * and tree and add to the address space's page tree also if not an anonymous
- * page
- * - should be called with mm->mmap_lock held writelocked
- */
-static void add_vma_to_mm(struct mm_struct *mm, struct vm_area_struct *vma)
+static void setup_vma_to_mm(struct vm_area_struct *vma, struct mm_struct *mm)
{
- struct address_space *mapping;
- struct vm_area_struct *prev;
- MA_STATE(mas, &mm->mm_mt, vma->vm_start, vma->vm_end);
-
- BUG_ON(!vma->vm_region);
-
mm->map_count++;
vma->vm_mm = mm;

/* add the VMA to the mapping */
if (vma->vm_file) {
- mapping = vma->vm_file->f_mapping;
+ struct address_space *mapping = vma->vm_file->f_mapping;

i_mmap_lock_write(mapping);
flush_dcache_mmap_lock(mapping);
@@ -584,21 +572,52 @@ static void add_vma_to_mm(struct mm_struct *mm, struct vm_area_struct *vma)
flush_dcache_mmap_unlock(mapping);
i_mmap_unlock_write(mapping);
}
+}

- prev = mas_prev(&mas, 0);
- mas_reset(&mas);
+/*
+ * mas_add_vma_to_mm() - Maple state variant of add_mas_to_mm().
+ * @mas: The maple state with preallocations.
+ * @mm: The mm_struct
+ * @vma: The vma to add
+ *
+ */
+static void mas_add_vma_to_mm(struct ma_state *mas, struct mm_struct *mm,
+ struct vm_area_struct *vma)
+{
+ struct vm_area_struct *prev;
+
+ BUG_ON(!vma->vm_region);
+
+ setup_vma_to_mm(vma, mm);
+
+ prev = mas_prev(mas, 0);
+ mas_reset(mas);
/* add the VMA to the tree */
- vma_mas_store(vma, &mas);
+ vma_mas_store(vma, mas);
__vma_link_list(mm, vma, prev);
}

/*
- * delete a VMA from its owning mm_struct and address space
+ * add a VMA into a process's mm_struct in the appropriate place in the list
+ * and tree and add to the address space's page tree also if not an anonymous
+ * page
+ * - should be called with mm->mmap_lock held writelocked
*/
-static void delete_vma_from_mm(struct vm_area_struct *vma)
+static int add_vma_to_mm(struct mm_struct *mm, struct vm_area_struct *vma)
{
- MA_STATE(mas, &vma->vm_mm->mm_mt, 0, 0);
+ MA_STATE(mas, &mm->mm_mt, vma->vm_start, vma->vm_end);
+
+ if (mas_preallocate(&mas, vma, GFP_KERNEL)) {
+ pr_warn("Allocation of vma tree for process %d failed\n",
+ current->pid);
+ return -ENOMEM;
+ }
+ mas_add_vma_to_mm(&mas, mm, vma);
+ return 0;
+}

+static void cleanup_vma_from_mm(struct vm_area_struct *vma)
+{
vma->vm_mm->map_count--;
/* remove the VMA from the mapping */
if (vma->vm_file) {
@@ -611,10 +630,25 @@ static void delete_vma_from_mm(struct vm_area_struct *vma)
flush_dcache_mmap_unlock(mapping);
i_mmap_unlock_write(mapping);
}
+}
+/*
+ * delete a VMA from its owning mm_struct and address space
+ */
+static int delete_vma_from_mm(struct vm_area_struct *vma)
+{
+ MA_STATE(mas, &vma->vm_mm->mm_mt, 0, 0);
+
+ if (mas_preallocate(&mas, vma, GFP_KERNEL)) {
+ pr_warn("Allocation of vma tree for process %d failed\n",
+ current->pid);
+ return -ENOMEM;
+ }
+ cleanup_vma_from_mm(vma);

/* remove from the MM's tree and list */
vma_mas_remove(vma, &mas);
__vma_unlink_list(vma->vm_mm, vma);
+ return 0;
}

/*
@@ -1024,6 +1058,7 @@ unsigned long do_mmap(struct file *file,
vm_flags_t vm_flags;
unsigned long capabilities, result;
int ret;
+ MA_STATE(mas, &current->mm->mm_mt, 0, 0);

*populate = 0;

@@ -1042,6 +1077,7 @@ unsigned long do_mmap(struct file *file,
* now know into VMA flags */
vm_flags = determine_vm_flags(file, prot, flags, capabilities);

+
/* we're going to need to record the mapping */
region = kmem_cache_zalloc(vm_region_jar, GFP_KERNEL);
if (!region)
@@ -1051,6 +1087,9 @@ unsigned long do_mmap(struct file *file,
if (!vma)
goto error_getting_vma;

+ if (mas_preallocate(&mas, vma, GFP_KERNEL))
+ goto error_maple_preallocate;
+
region->vm_usage = 1;
region->vm_flags = vm_flags;
region->vm_pgoff = pgoff;
@@ -1191,7 +1230,7 @@ unsigned long do_mmap(struct file *file,
current->mm->total_vm += len >> PAGE_SHIFT;

share:
- add_vma_to_mm(current->mm, vma);
+ mas_add_vma_to_mm(&mas, current->mm, vma);

/* we flush the region from the icache only when the first executable
* mapping of it is made */
@@ -1217,6 +1256,7 @@ unsigned long do_mmap(struct file *file,

sharing_violation:
up_write(&nommu_region_sem);
+ mas_destroy(&mas);
pr_warn("Attempt to share mismatched mappings\n");
ret = -EINVAL;
goto error;
@@ -1233,6 +1273,14 @@ unsigned long do_mmap(struct file *file,
len, current->pid);
show_free_areas(0, NULL);
return -ENOMEM;
+
+error_maple_preallocate:
+ kmem_cache_free(vm_region_jar, region);
+ vm_area_free(vma);
+ pr_warn("Allocation of vma tree for process %d failed\n", current->pid);
+ show_free_areas(0, NULL);
+ return -ENOMEM;
+
}

unsigned long ksys_mmap_pgoff(unsigned long addr, unsigned long len,
@@ -1298,6 +1346,7 @@ int split_vma(struct mm_struct *mm, struct vm_area_struct *vma,
struct vm_area_struct *new;
struct vm_region *region;
unsigned long npages;
+ MA_STATE(mas, &mm->mm_mt, vma->vm_start, vma->vm_end);

/* we're only permitted to split anonymous regions (these should have
* only a single usage on the region) */
@@ -1333,7 +1382,6 @@ int split_vma(struct mm_struct *mm, struct vm_area_struct *vma,
if (new->vm_ops && new->vm_ops->open)
new->vm_ops->open(new);

- delete_vma_from_mm(vma);
down_write(&nommu_region_sem);
delete_nommu_region(vma->vm_region);
if (new_below) {
@@ -1346,8 +1394,17 @@ int split_vma(struct mm_struct *mm, struct vm_area_struct *vma,
add_nommu_region(vma->vm_region);
add_nommu_region(new->vm_region);
up_write(&nommu_region_sem);
- add_vma_to_mm(mm, vma);
- add_vma_to_mm(mm, new);
+ if (mas_preallocate(&mas, vma, GFP_KERNEL)) {
+ pr_warn("Allocation of vma tree for process %d failed\n",
+ current->pid);
+ return -ENOMEM;
+ }
+
+ setup_vma_to_mm(vma, mm);
+ setup_vma_to_mm(new, mm);
+ mas_set_range(&mas, vma->vm_start, vma->vm_end - 1);
+ mas_store(&mas, vma);
+ vma_mas_store(new, &mas);
return 0;
}

@@ -1363,12 +1420,14 @@ static int shrink_vma(struct mm_struct *mm,

/* adjust the VMA's pointers, which may reposition it in the MM's tree
* and list */
- delete_vma_from_mm(vma);
+ if (delete_vma_from_mm(vma))
+ return -ENOMEM;
if (from > vma->vm_start)
vma->vm_end = from;
else
vma->vm_start = to;
- add_vma_to_mm(mm, vma);
+ if (add_vma_to_mm(mm, vma))
+ return -ENOMEM;

/* cut the backing region down to size */
region = vma->vm_region;
@@ -1396,9 +1455,10 @@ static int shrink_vma(struct mm_struct *mm,
*/
int do_munmap(struct mm_struct *mm, unsigned long start, size_t len, struct list_head *uf)
{
+ MA_STATE(mas, &mm->mm_mt, start, start);
struct vm_area_struct *vma;
unsigned long end;
- int ret;
+ int ret = 0;

len = PAGE_ALIGN(len);
if (len == 0)
@@ -1407,7 +1467,7 @@ int do_munmap(struct mm_struct *mm, unsigned long start, size_t len, struct list
end = start + len;

/* find the first potentially overlapping VMA */
- vma = find_vma(mm, start);
+ vma = mas_find(&mas, end - 1);
if (!vma) {
static int limit;
if (limit < 5) {
@@ -1426,7 +1486,7 @@ int do_munmap(struct mm_struct *mm, unsigned long start, size_t len, struct list
return -EINVAL;
if (end == vma->vm_end)
goto erase_whole_vma;
- vma = vma->vm_next;
+ vma = mas_next(&mas, end - 1);
} while (vma);
return -EINVAL;
} else {
@@ -1448,9 +1508,10 @@ int do_munmap(struct mm_struct *mm, unsigned long start, size_t len, struct list
}

erase_whole_vma:
- delete_vma_from_mm(vma);
+ if (delete_vma_from_mm(vma))
+ ret = -ENOMEM;
delete_vma(mm, vma);
- return 0;
+ return ret;
}

int vm_munmap(unsigned long addr, size_t len)
@@ -1475,6 +1536,7 @@ SYSCALL_DEFINE2(munmap, unsigned long, addr, size_t, len)
*/
void exit_mmap(struct mm_struct *mm)
{
+ VMA_ITERATOR(vmi, mm, 0);
struct vm_area_struct *vma;

if (!mm)
@@ -1482,13 +1544,18 @@ void exit_mmap(struct mm_struct *mm)

mm->total_vm = 0;

- while ((vma = mm->mmap)) {
- mm->mmap = vma->vm_next;
- delete_vma_from_mm(vma);
+ /*
+ * Lock the mm to avoid assert complaining even though this is the only
+ * user of the mm
+ */
+ mmap_write_lock(mm);
+ for_each_vma(vmi, vma) {
+ cleanup_vma_from_mm(vma);
delete_vma(mm, vma);
cond_resched();
}
__mt_destroy(&mm->mm_mt);
+ mmap_write_unlock(mm);
}

int vm_brk(unsigned long addr, unsigned long len)
--
2.35.1