Re: [PATCH v2 5/9] mm: vmalloc: Remove global purge_vmap_area_root rb-tree

Baoquan He
2023-09-11T02:58:04Z

On 08/29/23 at 10:11am, Uladzislau Rezki (Sony) wrote:
> Similar to busy VA, lazily-freed area is stored to a node
> it belongs to. Such approach does not require any global
> locking primitive, instead an access becomes scalable what
> mitigates a contention.
>
> This patch removes a global purge-lock, global purge-tree
> and global purge list.
>
> Signed-off-by: Uladzislau Rezki (Sony) <urezki@gmail.com>
> ---
> mm/vmalloc.c | 135 +++++++++++++++++++++++++++++++--------------------
> 1 file changed, 82 insertions(+), 53 deletions(-)

LGTM,

Reviewed-by: Baoquan He <bhe@redhat.com>

>
> diff --git a/mm/vmalloc.c b/mm/vmalloc.c
> index ae0368c314ff..5a8a9c1370b6 100644
> --- a/mm/vmalloc.c
> +++ b/mm/vmalloc.c
> @@ -733,10 +733,6 @@ static DEFINE_SPINLOCK(free_vmap_area_lock);
> LIST_HEAD(vmap_area_list);
> static bool vmap_initialized __read_mostly;
>
> -static struct rb_root purge_vmap_area_root = RB_ROOT;
> -static LIST_HEAD(purge_vmap_area_list);
> -static DEFINE_SPINLOCK(purge_vmap_area_lock);
> -
> /*
> * This kmem_cache is used for vmap_area objects. Instead of
> * allocating from slab we reuse an object from this cache to
> @@ -784,6 +780,12 @@ struct rb_list {
> struct vmap_node {
> /* Bookkeeping data of this node. */
> struct rb_list busy;
> + struct rb_list lazy;
> +
> + /*
> + * Ready-to-free areas.
> + */
> + struct list_head purge_list;
> };
>
> static struct vmap_node *nodes, snode;
> @@ -1768,40 +1770,22 @@ static DEFINE_MUTEX(vmap_purge_lock);
>
> /* for per-CPU blocks */
> static void purge_fragmented_blocks_allcpus(void);
> +static cpumask_t purge_nodes;
>
> /*
> * Purges all lazily-freed vmap areas.
> */
> -static bool __purge_vmap_area_lazy(unsigned long start, unsigned long end)
> +static unsigned long
> +purge_vmap_node(struct vmap_node *vn)
> {
> - unsigned long resched_threshold;
> - unsigned int num_purged_areas = 0;
> - struct list_head local_purge_list;
> + unsigned long num_purged_areas = 0;
> struct vmap_area *va, *n_va;
>
> - lockdep_assert_held(&vmap_purge_lock);
> -
> - spin_lock(&purge_vmap_area_lock);
> - purge_vmap_area_root = RB_ROOT;
> - list_replace_init(&purge_vmap_area_list, &local_purge_list);
> - spin_unlock(&purge_vmap_area_lock);
> -
> - if (unlikely(list_empty(&local_purge_list)))
> - goto out;
> -
> - start = min(start,
> - list_first_entry(&local_purge_list,
> - struct vmap_area, list)->va_start);
> -
> - end = max(end,
> - list_last_entry(&local_purge_list,
> - struct vmap_area, list)->va_end);
> -
> - flush_tlb_kernel_range(start, end);
> - resched_threshold = lazy_max_pages() << 1;
> + if (list_empty(&vn->purge_list))
> + return 0;
>
> spin_lock(&free_vmap_area_lock);
> - list_for_each_entry_safe(va, n_va, &local_purge_list, list) {
> + list_for_each_entry_safe(va, n_va, &vn->purge_list, list) {
> unsigned long nr = (va->va_end - va->va_start) >> PAGE_SHIFT;
> unsigned long orig_start = va->va_start;
> unsigned long orig_end = va->va_end;
> @@ -1823,13 +1807,55 @@ static bool __purge_vmap_area_lazy(unsigned long start, unsigned long end)
>
> atomic_long_sub(nr, &vmap_lazy_nr);
> num_purged_areas++;
> -
> - if (atomic_long_read(&vmap_lazy_nr) < resched_threshold)
> - cond_resched_lock(&free_vmap_area_lock);
> }
> spin_unlock(&free_vmap_area_lock);
>
> -out:
> + return num_purged_areas;
> +}
> +
> +/*
> + * Purges all lazily-freed vmap areas.
> + */
> +static bool __purge_vmap_area_lazy(unsigned long start, unsigned long end)
> +{
> + unsigned long num_purged_areas = 0;
> + struct vmap_node *vn;
> + int i;
> +
> + lockdep_assert_held(&vmap_purge_lock);
> + purge_nodes = CPU_MASK_NONE;
> +
> + for (i = 0; i < nr_nodes; i++) {
> + vn = &nodes[i];
> +
> + INIT_LIST_HEAD(&vn->purge_list);
> +
> + if (RB_EMPTY_ROOT(&vn->lazy.root))
> + continue;
> +
> + spin_lock(&vn->lazy.lock);
> + WRITE_ONCE(vn->lazy.root.rb_node, NULL);
> + list_replace_init(&vn->lazy.head, &vn->purge_list);
> + spin_unlock(&vn->lazy.lock);
> +
> + start = min(start, list_first_entry(&vn->purge_list,
> + struct vmap_area, list)->va_start);
> +
> + end = max(end, list_last_entry(&vn->purge_list,
> + struct vmap_area, list)->va_end);
> +
> + cpumask_set_cpu(i, &purge_nodes);
> + }
> +
> + if (cpumask_weight(&purge_nodes) > 0) {
> + flush_tlb_kernel_range(start, end);
> +
> + for_each_cpu(i, &purge_nodes) {
> + vn = &nodes[i];
> + num_purged_areas += purge_vmap_node(vn);
> + }
> + }
> +
> trace_purge_vmap_area_lazy(start, end, num_purged_areas);
> return num_purged_areas > 0;
> }
> @@ -1848,16 +1874,9 @@ static void reclaim_and_purge_vmap_areas(void)
>
> static void drain_vmap_area_work(struct work_struct *work)
> {
> - unsigned long nr_lazy;
> -
> - do {
> - mutex_lock(&vmap_purge_lock);
> - __purge_vmap_area_lazy(ULONG_MAX, 0);
> - mutex_unlock(&vmap_purge_lock);
> -
> - /* Recheck if further work is required. */
> - nr_lazy = atomic_long_read(&vmap_lazy_nr);
> - } while (nr_lazy > lazy_max_pages());
> + mutex_lock(&vmap_purge_lock);
> + __purge_vmap_area_lazy(ULONG_MAX, 0);
> + mutex_unlock(&vmap_purge_lock);
> }
>
> /*
> @@ -1867,6 +1886,7 @@ static void drain_vmap_area_work(struct work_struct *work)
> */
> static void free_vmap_area_noflush(struct vmap_area *va)
> {
> + struct vmap_node *vn = addr_to_node(va->va_start);
> unsigned long nr_lazy_max = lazy_max_pages();
> unsigned long va_start = va->va_start;
> unsigned long nr_lazy;
> @@ -1880,10 +1900,9 @@ static void free_vmap_area_noflush(struct vmap_area *va)
> /*
> * Merge or place it to the purge tree/list.
> */
> - spin_lock(&purge_vmap_area_lock);
> - merge_or_add_vmap_area(va,
> - &purge_vmap_area_root, &purge_vmap_area_list);
> - spin_unlock(&purge_vmap_area_lock);
> + spin_lock(&vn->lazy.lock);
> + merge_or_add_vmap_area(va, &vn->lazy.root, &vn->lazy.head);
> + spin_unlock(&vn->lazy.lock);
>
> trace_free_vmap_area_noflush(va_start, nr_lazy, nr_lazy_max);
>
> @@ -4390,15 +4409,21 @@ static void show_numa_info(struct seq_file *m, struct vm_struct *v)
>
> static void show_purge_info(struct seq_file *m)
> {
> + struct vmap_node *vn;
> struct vmap_area *va;
> + int i;
>
> - spin_lock(&purge_vmap_area_lock);
> - list_for_each_entry(va, &purge_vmap_area_list, 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);
> + for (i = 0; i < nr_nodes; i++) {
> + vn = &nodes[i];
> +
> + spin_lock(&vn->lazy.lock);
> + list_for_each_entry(va, &vn->lazy.head, 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);
> + }
> + spin_unlock(&vn->lazy.lock);
> }
> - spin_unlock(&purge_vmap_area_lock);
> }
>
> static int s_show(struct seq_file *m, void *p)
> @@ -4545,6 +4570,10 @@ static void vmap_init_nodes(void)
> vn->busy.root = RB_ROOT;
> INIT_LIST_HEAD(&vn->busy.head);
> spin_lock_init(&vn->busy.lock);
> +
> + vn->lazy.root = RB_ROOT;
> + INIT_LIST_HEAD(&vn->lazy.head);
> + spin_lock_init(&vn->lazy.lock);
> }
> }
>
> --
> 2.30.2
>