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Subject[PATCH v4 1/2] mm/vmalloc: do not keep unpurged areas in the busy tree
Date
From: "Uladzislau Rezki (Sony)" <urezki@gmail.com>

The busy tree can be quite big, even though the area is freed
or unmapped it still stays there until "purge" logic removes
it.

1) Optimize and reduce the size of "busy" tree by removing a
node from it right away as soon as user triggers free paths.
It is possible to do so, because the allocation is done using
another augmented tree.

The vmalloc test driver shows the difference, for example the
"fix_size_alloc_test" is ~11% better comparing with default
configuration:

sudo ./test_vmalloc.sh performance

<default>
Summary: fix_size_alloc_test loops: 1000000 avg: 993985 usec
Summary: full_fit_alloc_test loops: 1000000 avg: 973554 usec
Summary: long_busy_list_alloc_test loops: 1000000 avg: 12617652 usec
<default>

<this patch>
Summary: fix_size_alloc_test loops: 1000000 avg: 882263 usec
Summary: full_fit_alloc_test loops: 1000000 avg: 973407 usec
Summary: long_busy_list_alloc_test loops: 1000000 avg: 12593929 usec
<this patch>

2) Since the busy tree now contains allocated areas only and does
not interfere with lazily free nodes, introduce the new function
show_purge_info() that dumps "unpurged" areas that is propagated
through "/proc/vmallocinfo".

3) Eliminate VM_LAZY_FREE flag.

Signed-off-by: Uladzislau Rezki (Sony) <urezki@gmail.com>
---
mm/vmalloc.c | 51 ++++++++++++++++++++++++++++++++++++++++++---------
1 file changed, 42 insertions(+), 9 deletions(-)

diff --git a/mm/vmalloc.c b/mm/vmalloc.c
index 4fa8d84599b0..9eb700a2087b 100644
--- a/mm/vmalloc.c
+++ b/mm/vmalloc.c
@@ -329,7 +329,6 @@ EXPORT_SYMBOL(vmalloc_to_pfn);
#define DEBUG_AUGMENT_PROPAGATE_CHECK 0
#define DEBUG_AUGMENT_LOWEST_MATCH_CHECK 0

-#define VM_LAZY_FREE 0x02
#define VM_VM_AREA 0x04

static DEFINE_SPINLOCK(vmap_area_lock);
@@ -541,7 +540,7 @@ link_va(struct vmap_area *va, struct rb_root *root,
static __always_inline void
unlink_va(struct vmap_area *va, struct rb_root *root)
{
- if (WARN_ON(RB_EMPTY_NODE(&va->rb_node)))
+ if (RB_EMPTY_NODE(&va->rb_node))
return;

if (root == &free_vmap_area_root)
@@ -1167,7 +1166,11 @@ EXPORT_SYMBOL_GPL(unregister_vmap_purge_notifier);
static void __free_vmap_area(struct vmap_area *va)
{
/*
- * Remove from the busy tree/list.
+ * In most cases VA is not attached to the tree, but there
+ * are a few exceptions:
+ *
+ * - is linked only in case of pcpu, recovery part;
+ * - if radix_tree_preload gets failed, see new_vmap_block().
*/
unlink_va(va, &vmap_area_root);

@@ -1318,6 +1321,10 @@ static void free_vmap_area_noflush(struct vmap_area *va)
{
unsigned long nr_lazy;

+ spin_lock(&vmap_area_lock);
+ unlink_va(va, &vmap_area_root);
+ spin_unlock(&vmap_area_lock);
+
nr_lazy = atomic_long_add_return((va->va_end - va->va_start) >>
PAGE_SHIFT, &vmap_lazy_nr);

@@ -2137,14 +2144,13 @@ struct vm_struct *remove_vm_area(const void *addr)

might_sleep();

- va = find_vmap_area((unsigned long)addr);
+ spin_lock(&vmap_area_lock);
+ va = __find_vmap_area((unsigned long)addr);
if (va && va->flags & VM_VM_AREA) {
struct vm_struct *vm = va->vm;

- spin_lock(&vmap_area_lock);
va->vm = NULL;
va->flags &= ~VM_VM_AREA;
- va->flags |= VM_LAZY_FREE;
spin_unlock(&vmap_area_lock);

kasan_free_shadow(vm);
@@ -2152,6 +2158,8 @@ struct vm_struct *remove_vm_area(const void *addr)

return vm;
}
+
+ spin_unlock(&vmap_area_lock);
return NULL;
}

@@ -3431,6 +3439,22 @@ static void show_numa_info(struct seq_file *m, struct vm_struct *v)
}
}

+static void show_purge_info(struct seq_file *m)
+{
+ struct llist_node *head;
+ struct vmap_area *va;
+
+ head = READ_ONCE(vmap_purge_list.first);
+ if (head == NULL)
+ return;
+
+ llist_for_each_entry(va, head, purge_list) {
+ seq_printf(m, "0x%pK-0x%pK %7ld unpurged vm_area\n",
+ (void *)va->va_start, (void *)va->va_end,
+ va->va_end - va->va_start);
+ }
+}
+
static int s_show(struct seq_file *m, void *p)
{
struct vmap_area *va;
@@ -3443,10 +3467,9 @@ static int s_show(struct seq_file *m, void *p)
* behalf of vmap area is being tear down or vm_map_ram allocation.
*/
if (!(va->flags & VM_VM_AREA)) {
- seq_printf(m, "0x%pK-0x%pK %7ld %s\n",
+ seq_printf(m, "0x%pK-0x%pK %7ld vm_map_ram\n",
(void *)va->va_start, (void *)va->va_end,
- va->va_end - va->va_start,
- va->flags & VM_LAZY_FREE ? "unpurged vm_area" : "vm_map_ram");
+ va->va_end - va->va_start);

return 0;
}
@@ -3482,6 +3505,16 @@ static int s_show(struct seq_file *m, void *p)

show_numa_info(m, v);
seq_putc(m, '\n');
+
+ /*
+ * As a final step, dump "unpurged" areas. Note,
+ * that entire "/proc/vmallocinfo" output will not
+ * be address sorted, because the purge list is not
+ * sorted.
+ */
+ if (list_is_last(&va->list, &vmap_area_list))
+ show_purge_info(m);
+
return 0;
}

--
2.21.0
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