Re: [patch 0/6] mm/vmalloc: Assorted fixes and improvements

Thomas Gleixner
2023-05-23T18:40:14Z

On Tue, May 23 2023 at 19:55, Uladzislau Rezki wrote:
> On Tue, May 23, 2023 at 07:48:09PM +0200, Uladzislau Rezki wrote:
>> So, v6.3 does not contain that patch. I have to use the next instead.
>>
> next-20230523:

It works against linus tree just fine.

> mm/vmalloc.c: In function ‘_vm_unmap_aliases’:
> mm/vmalloc.c:2280:9: error: too few arguments to function ‘purge_fragmented_block’
> 2280 | if (!purge_fragmented_block(vb, vbq, &purge_list) &&
> | ^~~~~~~~~~~~~~~~~~~~~~
> mm/vmalloc.c:2095:13: note: declared here
> 2095 | static bool purge_fragmented_block(struct vmap_block *vb, struct vmap_block_queue *vbq,
> | ^~~~~~~~~~~~~~~~~~~~~~
> CC drivers/acpi/pmic/intel_pmic_bxtwc.o
>
>
> there is only one complain in fact.

That's the one where I failed to pull the refreshed patch back from the
test machine.

---
Subject: mm/vmalloc: Don't purge usable blocks unnecessarily
From: Thomas Gleixner <tglx@linutronix.de>
Date: Mon, 22 May 2023 19:38:32 +0200

Purging fragmented blocks is done unconditionally in several contexts:

1) From drain_vmap_area_work(), when the number of lazy to be freed
vmap_areas reached the threshold

2) Reclaiming vmalloc address space from pcpu_get_vm_areas()

3) _unmap_aliases()

#1 There is no reason to zap fragmented vmap blocks unconditionally, simply
because reclaiming all lazy areas drains at least

32MB * fls(num_online_cpus())

per invocation which is plenty.

#2 Reclaiming when running out of space or due to memory pressure makes a
lot of sense

#3 _unmap_aliases() requires to touch everything because the caller has no
clue which vmap_area used a particular page last and the vmap_area lost
that information too.

Except for the vfree + VM_FLUSH_RESET_PERMS case, which removes the
vmap area first and then cares about the flush. That in turn requires
a full walk of _all_ vmap areas including the one which was just
added to the purge list.

But as this has to be flushed anyway this is an opportunity to combine
outstanding TLB flushes and do the housekeeping of purging freed areas,
but like #1 there is no real good reason to zap usable vmap blocks
unconditionally.

Add a @force_purge argument to the relevant functions and if not true only
purge fragmented blocks which have less than 1/4 of their capacity left.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
---
mm/vmalloc.c | 36 +++++++++++++++++++++++-------------
1 file changed, 23 insertions(+), 13 deletions(-)

--- a/mm/vmalloc.c
+++ b/mm/vmalloc.c
@@ -791,7 +791,7 @@ get_subtree_max_size(struct rb_node *nod
RB_DECLARE_CALLBACKS_MAX(static, free_vmap_area_rb_augment_cb,
struct vmap_area, rb_node, unsigned long, subtree_max_size, va_size)

-static void purge_vmap_area_lazy(void);
+static void purge_vmap_area_lazy(bool force_purge);
static BLOCKING_NOTIFIER_HEAD(vmap_notify_list);
static void drain_vmap_area_work(struct work_struct *work);
static DECLARE_WORK(drain_vmap_work, drain_vmap_area_work);
@@ -1649,7 +1649,7 @@ static struct vmap_area *alloc_vmap_area

overflow:
if (!purged) {
- purge_vmap_area_lazy();
+ purge_vmap_area_lazy(true);
purged = 1;
goto retry;
}
@@ -1717,7 +1717,7 @@ static atomic_long_t vmap_lazy_nr = ATOM
static DEFINE_MUTEX(vmap_purge_lock);

/* for per-CPU blocks */
-static void purge_fragmented_blocks_allcpus(void);
+static void purge_fragmented_blocks_allcpus(bool force_purge);

/*
* Purges all lazily-freed vmap areas.
@@ -1787,10 +1787,10 @@ static bool __purge_vmap_area_lazy(unsig
/*
* Kick off a purge of the outstanding lazy areas.
*/
-static void purge_vmap_area_lazy(void)
+static void purge_vmap_area_lazy(bool force_purge)
{
mutex_lock(&vmap_purge_lock);
- purge_fragmented_blocks_allcpus();
+ purge_fragmented_blocks_allcpus(force_purge);
__purge_vmap_area_lazy(ULONG_MAX, 0);
mutex_unlock(&vmap_purge_lock);
}
@@ -1908,6 +1908,12 @@ static struct vmap_area *find_unlink_vma

#define VMAP_BLOCK_SIZE (VMAP_BBMAP_BITS * PAGE_SIZE)

+/*
+ * Purge threshold to prevent overeager purging of fragmented blocks for
+ * regular operations: Purge if vb->free is less than 1/4 of the capacity.
+ */
+#define VMAP_PURGE_THRESHOLD (VMAP_BBMAP_BITS / 4)
+
#define VMAP_RAM 0x1 /* indicates vm_map_ram area*/
#define VMAP_BLOCK 0x2 /* mark out the vmap_block sub-type*/
#define VMAP_FLAGS_MASK 0x3
@@ -2087,12 +2093,16 @@ static void free_vmap_block(struct vmap_
}

static bool purge_fragmented_block(struct vmap_block *vb, struct vmap_block_queue *vbq,
- struct list_head *purge_list)
+ struct list_head *purge_list, bool force_purge)
{
if (!(vb->free + vb->dirty == VMAP_BBMAP_BITS && vb->dirty != VMAP_BBMAP_BITS))
return false;

- /* prevent further allocs after releasing lock */
+ /* Don't overeagerly purge usable blocks unless requested */
+ if (!force_purge && vb->free < VMAP_PURGE_THRESHOLD)
+ return false;
+
+ /* prevent further allocs after releasing lock */
WRITE_ONCE(vb->free, 0);
/* prevent purging it again */
WRITE_ONCE(vb->dirty, VMAP_BBMAP_BITS);
@@ -2115,7 +2125,7 @@ static void free_purged_blocks(struct li
}
}

-static void purge_fragmented_blocks(int cpu)
+static void purge_fragmented_blocks(int cpu, bool force_purge)
{
LIST_HEAD(purge);
struct vmap_block *vb;
@@ -2130,19 +2140,19 @@ static void purge_fragmented_blocks(int
continue;

spin_lock(&vb->lock);
- purge_fragmented_block(vb, vbq, &purge);
+ purge_fragmented_block(vb, vbq, &purge, force_purge);
spin_unlock(&vb->lock);
}
rcu_read_unlock();
free_purged_blocks(&purge);
}

-static void purge_fragmented_blocks_allcpus(void)
+static void purge_fragmented_blocks_allcpus(bool force_purge)
{
int cpu;

for_each_possible_cpu(cpu)
- purge_fragmented_blocks(cpu);
+ purge_fragmented_blocks(cpu, force_purge);
}

static void *vb_alloc(unsigned long size, gfp_t gfp_mask)
@@ -2267,7 +2277,7 @@ static void _vm_unmap_aliases(unsigned l
* not purgeable, check whether there is dirty
* space to be flushed.
*/
- if (!purge_fragmented_block(vb, vbq, &purge_list) &&
+ if (!purge_fragmented_block(vb, vbq, &purge_list, false) &&
vb->dirty_max && vb->dirty != VMAP_BBMAP_BITS) {
unsigned long va_start = vb->va->va_start;
unsigned long s, e;
@@ -4173,7 +4183,7 @@ struct vm_struct **pcpu_get_vm_areas(con
overflow:
spin_unlock(&free_vmap_area_lock);
if (!purged) {
- purge_vmap_area_lazy();
+ purge_vmap_area_lazy(true);
purged = true;

/* Before "retry", check if we recover. */