Re: [PATCH] mm/vmalloc: Remove WARN_ON_ONCE related to adjust_va_to_fit_type

[Uladzislau Rezki]

> > Yes, but GFP_NOWAIT-alloc-error can easily occur for low-memory device.
> >
> Agree. You are really in a low memory condition. We end up here only if
> pre-loading also has not succeeded, i.e. GFP_KERNEL also fails.
> 
> But i agree with you, we should "improve the warning" because we drain
> and repeat.
> 
> > How about changing fix as below?:
> > 
> > <snip>
> > --- a/mm/vmalloc.c
> > +++ b/mm/vmalloc.c
> > @@ -1468,6 +1468,7 @@ adjust_va_to_fit_type(struct rb_root *root, struct list_head *head,
> >                  */
> >                 va->va_start = nva_start_addr + size;
> >         } else {
> > +               WARN_ON_ONCE(1);
> >                 return -1;
> >         }
> >  
> > @@ -1522,7 +1523,7 @@ __alloc_vmap_area(struct rb_root *root, struct list_head *head,
> >  
> >         /* Update the free vmap_area. */
> >         ret = adjust_va_to_fit_type(root, head, va, nva_start_addr, size);
> > -       if (WARN_ON_ONCE(ret))
> > +       if (ret)
> >                 return vend;
> >  
> >  #if DEBUG_AUGMENT_LOWEST_MATCH_CHECK
> > @@ -4143,7 +4144,7 @@ struct vm_struct **pcpu_get_vm_areas(const unsigned long *offsets,
> >                 ret = adjust_va_to_fit_type(&free_vmap_area_root,
> >                                             &free_vmap_area_list,
> >                                             va, start, size);
> > -               if (WARN_ON_ONCE(unlikely(ret)))
> > +               if (unlikely(ret))
> >                         /* It is a BUG(), but trigger recovery instead. */
> >                         goto recovery;
> >  
> > <snip>
> > It will WARN_ONCE_ONCE() only if classify_va_fit_type() is "(type == NOTHING_FIT)".
> > 
> This is good but i think it should be improved further. We need to
> understand from the warning when no memory and when there is no a
> vmap space, so:
> 
> - if NOTHING_FIT, we should WARN() for sure;
> - Second place in the pcpu_get_vm_area(), we do not use NE_FIT. Only in
>   the begging after boot, but potentially we can trigger -ENOMEM and we
>   should warn in this case. Otherwise you just hide it;
> - And last one if after repeating we still do not manage to allocate.
> 

We should understand a reason of failing. I think error handling should
be improved. Something like:

<snip>
diff --git a/mm/vmalloc.c b/mm/vmalloc.c
index ef8599d394fd..03a36921a3fc 100644
--- a/mm/vmalloc.c
+++ b/mm/vmalloc.c
@@ -1454,7 +1454,7 @@ adjust_va_to_fit_type(struct rb_root *root, struct list_head *head,
 			 */
 			lva = kmem_cache_alloc(vmap_area_cachep, GFP_NOWAIT);
 			if (!lva)
-				return -1;
+				return -ENOMEM;
 		}
 
 		/*
@@ -1468,7 +1468,7 @@ adjust_va_to_fit_type(struct rb_root *root, struct list_head *head,
 		 */
 		va->va_start = nva_start_addr + size;
 	} else {
-		return -1;
+		return -EINVAL;
 	}
 
 	if (type != FL_FIT_TYPE) {
@@ -1488,7 +1488,8 @@ adjust_va_to_fit_type(struct rb_root *root, struct list_head *head,
 static __always_inline unsigned long
 __alloc_vmap_area(struct rb_root *root, struct list_head *head,
 	unsigned long size, unsigned long align,
-	unsigned long vstart, unsigned long vend)
+	unsigned long vstart, unsigned long vend,
+	int *error)
 {
 	bool adjust_search_size = true;
 	unsigned long nva_start_addr;
@@ -1508,8 +1509,10 @@ __alloc_vmap_area(struct rb_root *root, struct list_head *head,
 		adjust_search_size = false;
 
 	va = find_vmap_lowest_match(root, size, align, vstart, adjust_search_size);
-	if (unlikely(!va))
+	if (unlikely(!va)) {
+		*error = -ENOENT;
 		return vend;
+	}
 
 	if (va->va_start > vstart)
 		nva_start_addr = ALIGN(va->va_start, align);
@@ -1517,13 +1520,17 @@ __alloc_vmap_area(struct rb_root *root, struct list_head *head,
 		nva_start_addr = ALIGN(vstart, align);
 
 	/* Check the "vend" restriction. */
-	if (nva_start_addr + size > vend)
+	if (nva_start_addr + size > vend) {
+		*error = -ERANGE;
 		return vend;
+	}
 
 	/* Update the free vmap_area. */
 	ret = adjust_va_to_fit_type(root, head, va, nva_start_addr, size);
-	if (WARN_ON_ONCE(ret))
+	if (ret) {
+		*error = ret;
 		return vend;
+	}
 
 #if DEBUG_AUGMENT_LOWEST_MATCH_CHECK
 	find_vmap_lowest_match_check(root, head, size, align);
@@ -1589,7 +1596,7 @@ static struct vmap_area *alloc_vmap_area(unsigned long size,
 	unsigned long freed;
 	unsigned long addr;
 	int purged = 0;
-	int ret;
+	int ret, error;
 
 	if (unlikely(!size || offset_in_page(size) || !is_power_of_2(align)))
 		return ERR_PTR(-EINVAL);
@@ -1613,7 +1620,7 @@ static struct vmap_area *alloc_vmap_area(unsigned long size,
 retry:
 	preload_this_cpu_lock(&free_vmap_area_lock, gfp_mask, node);
 	addr = __alloc_vmap_area(&free_vmap_area_root, &free_vmap_area_list,
-		size, align, vstart, vend);
+		size, align, vstart, vend, &error);
 	spin_unlock(&free_vmap_area_lock);
 
 	trace_alloc_vmap_area(addr, size, align, vstart, vend, addr == vend);
@@ -1662,8 +1669,9 @@ static struct vmap_area *alloc_vmap_area(unsigned long size,
 	}
 
 	if (!(gfp_mask & __GFP_NOWARN) && printk_ratelimit())
-		pr_warn("vmap allocation for size %lu failed: use vmalloc=<size> to increase size\n",
-			size);
+		pr_warn("vmap allocation for size %lu failed: "
+			"use vmalloc=<size> to increase size, errno: (%d)\n",
+			size, error);
 
 	kmem_cache_free(vmap_area_cachep, va);
 	return ERR_PTR(-EBUSY);
@@ -4143,9 +4151,10 @@ struct vm_struct **pcpu_get_vm_areas(const unsigned long *offsets,
 		ret = adjust_va_to_fit_type(&free_vmap_area_root,
 					    &free_vmap_area_list,
 					    va, start, size);
-		if (WARN_ON_ONCE(unlikely(ret)))
-			/* It is a BUG(), but trigger recovery instead. */
+		if (unlikely(ret)) {
+			WARN_ONCE(1, "%s error: errno (%d)\n", __func__, ret);
 			goto recovery;
+		}
 
 		/* Allocated area. */
 		va = vas[area];
<snip>

Any thoughts?

--
Uladzislau Rezki