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mm: vmalloc: remove global purge_vmap_area_root rb-tree
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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.

Link: https://lkml.kernel.org/r/20240102184633.748113-7-urezki@gmail.com
Signed-off-by: Uladzislau Rezki (Sony) <urezki@gmail.com>
Reviewed-by: Baoquan He <bhe@redhat.com>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Dave Chinner <david@fromorbit.com>
Cc: Joel Fernandes (Google) <joel@joelfernandes.org>
Cc: Kazuhito Hagio <k-hagio-ab@nec.com>
Cc: Liam R. Howlett <Liam.Howlett@oracle.com>
Cc: Lorenzo Stoakes <lstoakes@gmail.com>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Oleksiy Avramchenko <oleksiy.avramchenko@sony.com>
Cc: Paul E. McKenney <paulmck@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
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@urezki @akpm00
urezki authored and akpm00 committed Feb 24, 2024
1 parent 55c49fe commit 282631c
Showing 1 changed file with 82 additions and 53 deletions.
135 changes: 82 additions & 53 deletions mm/vmalloc.c
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Original file line number Diff line number Diff line change
Expand Up @@ -731,10 +731,6 @@ EXPORT_SYMBOL(vmalloc_to_pfn);
static DEFINE_SPINLOCK(free_vmap_area_lock);
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
Expand Down Expand Up @@ -782,6 +778,12 @@ struct rb_list {
static 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;
} single;

static struct vmap_node *vmap_nodes = &single;
Expand Down Expand Up @@ -1766,40 +1768,22 @@ 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;
Expand All @@ -1821,13 +1805,55 @@ 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_vmap_nodes; i++) {
vn = &vmap_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;
}
Expand All @@ -1846,16 +1872,9 @@ 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);
}

/*
Expand All @@ -1865,6 +1884,7 @@ 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;
Expand All @@ -1878,10 +1898,9 @@ 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);

Expand Down Expand Up @@ -4411,15 +4430,21 @@ 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_vmap_nodes; i++) {
vn = &vmap_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)
Expand Down Expand Up @@ -4558,6 +4583,10 @@ 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);
}
}

Expand Down

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