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Date: Wed, 27 Sep 2023 17:25:36 +0200
From: Uladzislau Rezki <urezki@...il.com>
To: "bhe@...hat.com" <bhe@...hat.com>,
Jaeseon Sim <jason.sim@...sung.com>
Cc: Uladzislau Rezki <urezki@...il.com>,
Jaeseon Sim <jason.sim@...sung.com>,
"akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
"hch@...radead.org" <hch@...radead.org>,
"lstoakes@...il.com" <lstoakes@...il.com>,
"linux-mm@...ck.org" <linux-mm@...ck.org>,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
Jaewon Kim <jaewon31.kim@...sung.com>
Subject: Re: [PATCH] mm/vmalloc: Remove WARN_ON_ONCE related to
adjust_va_to_fit_type
On Wed, Sep 27, 2023 at 09:33:04PM +0800, bhe@...hat.com wrote:
> On 09/27/23 at 01:49pm, Uladzislau Rezki wrote:
> > > > 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:
>
> This looks good to me, while the parameter 'error' looks a little ugly.
> How about this?
>
Agree. Embedding an error to "addr" is much more better way of handling
it, so we do not need an extra storage for errors. This is good :)
Jaeseon Sim - do you agree on it? If so please re-spin the patch if you
do not want please let us know.
> diff --git a/mm/vmalloc.c b/mm/vmalloc.c
> index ef8599d394fd..32805c82373b 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) {
> @@ -1509,7 +1509,7 @@ __alloc_vmap_area(struct rb_root *root, struct list_head *head,
>
> va = find_vmap_lowest_match(root, size, align, vstart, adjust_search_size);
> if (unlikely(!va))
> - return vend;
> + return -ENOENT;
>
> if (va->va_start > vstart)
> nva_start_addr = ALIGN(va->va_start, align);
> @@ -1518,12 +1518,12 @@ __alloc_vmap_area(struct rb_root *root, struct list_head *head,
>
> /* Check the "vend" restriction. */
> if (nva_start_addr + size > vend)
> - return vend;
> + return -ERANGE;
>
> /* Update the free vmap_area. */
> ret = adjust_va_to_fit_type(root, head, va, nva_start_addr, size);
> - if (WARN_ON_ONCE(ret))
> - return vend;
> + if (ret)
> + return ret;
>
> #if DEBUG_AUGMENT_LOWEST_MATCH_CHECK
> find_vmap_lowest_match_check(root, head, size, align);
> @@ -1616,13 +1616,13 @@ static struct vmap_area *alloc_vmap_area(unsigned long size,
> size, align, vstart, vend);
> spin_unlock(&free_vmap_area_lock);
>
> - trace_alloc_vmap_area(addr, size, align, vstart, vend, addr == vend);
> + trace_alloc_vmap_area(addr, size, align, vstart, vend, IS_ERR(addr));
>
> /*
> - * If an allocation fails, the "vend" address is
> + * If an allocation fails, the error value is
> * returned. Therefore trigger the overflow path.
> */
> - if (unlikely(addr == vend))
> + if (unlikely(IS_ERR(addr)))
> goto overflow;
>
> va->va_start = addr;
> @@ -1662,8 +1662,9 @@ 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, addr);
>
> kmem_cache_free(vmap_area_cachep, va);
> return ERR_PTR(-EBUSY);
> @@ -4143,8 +4144,8 @@ 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. */
>
> >
> > <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
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