[v3,1/2] mm/vmalloc: add vmalloc_no_huge

Commit Message

Claudio Imbrenda June 10, 2021, 3:42 p.m. UTC

The recent patches to add support for hugepage vmalloc mappings added a
flag for __vmalloc_node_range to allow to request small pages.
This flag is not accessible when calling vmalloc, the only option is to
call directly __vmalloc_node_range, which is not exported.

This means that a module can't vmalloc memory with small pages.

Case in point: KVM on s390x needs to vmalloc a large area, and it needs
to be mapped with small pages, because of a hardware limitation.

This patch adds the function vmalloc_no_huge, which works like vmalloc,
but it is guaranteed to always back the mapping using small pages. This
function is exported, therefore it is usable by modules.

Signed-off-by: Claudio Imbrenda <[e-mail]>
Cc: Andrew Morton <[e-mail]>
Cc: Nicholas Piggin <[e-mail]>
Cc: Uladzislau Rezki (Sony) <[e-mail]>
Cc: Catalin Marinas <[e-mail]>
Cc: Thomas Gleixner <[e-mail]>
Cc: Ingo Molnar <[e-mail]>
Cc: David Rientjes <[e-mail]>
Cc: Christoph Hellwig <[e-mail]>
---
 include/linux/vmalloc.h |  1 +
 mm/vmalloc.c            | 16 ++++++++++++++++
 2 files changed, 17 insertions(+)

Comments

Uladzislau Rezki June 10, 2021, 7:31 p.m. UTC | #1

Hello.

See below a small nit:

> The recent patches to add support for hugepage vmalloc mappings added a
> flag for __vmalloc_node_range to allow to request small pages.
> This flag is not accessible when calling vmalloc, the only option is to
> call directly __vmalloc_node_range, which is not exported.
> 
> This means that a module can't vmalloc memory with small pages.
> 
> Case in point: KVM on s390x needs to vmalloc a large area, and it needs
> to be mapped with small pages, because of a hardware limitation.
> 
> This patch adds the function vmalloc_no_huge, which works like vmalloc,
> but it is guaranteed to always back the mapping using small pages. This
> function is exported, therefore it is usable by modules.
> 
> Signed-off-by: Claudio Imbrenda <[e-mail]>
> Cc: Andrew Morton <[e-mail]>
> Cc: Nicholas Piggin <[e-mail]>
> Cc: Uladzislau Rezki (Sony) <[e-mail]>
> Cc: Catalin Marinas <[e-mail]>
> Cc: Thomas Gleixner <[e-mail]>
> Cc: Ingo Molnar <[e-mail]>
> Cc: David Rientjes <[e-mail]>
> Cc: Christoph Hellwig <[e-mail]>
> ---
>  include/linux/vmalloc.h |  1 +
>  mm/vmalloc.c            | 16 ++++++++++++++++
>  2 files changed, 17 insertions(+)
> 
> diff --git a/include/linux/vmalloc.h b/include/linux/vmalloc.h
> index 4d668abb6391..bfaaf0b6fa76 100644
> --- a/include/linux/vmalloc.h
> +++ b/include/linux/vmalloc.h
> @@ -135,6 +135,7 @@ extern void *__vmalloc_node_range(unsigned long size, unsigned long align,
>  			const void *caller);
>  void *__vmalloc_node(unsigned long size, unsigned long align, gfp_t gfp_mask,
>  		int node, const void *caller);
> +void *vmalloc_no_huge(unsigned long size);
>  
>  extern void vfree(const void *addr);
>  extern void vfree_atomic(const void *addr);
> diff --git a/mm/vmalloc.c b/mm/vmalloc.c
> index a13ac524f6ff..296a2fcc3fbe 100644
> --- a/mm/vmalloc.c
> +++ b/mm/vmalloc.c
> @@ -2998,6 +2998,22 @@ void *vmalloc(unsigned long size)
>  }
>  EXPORT_SYMBOL(vmalloc);
>  
> +/**
> + * vmalloc_no_huge - allocate virtually contiguous memory using small pages
> + * @size:    allocation size
> + *
You state that it allocates using "small pages". I think it might be confused 
for people because of that vague meaning. The comment should be improved, imho,
saying rather about order-0 pages what we call "small pages".

> + * Allocate enough non-huge pages to cover @size from the page level
> + * allocator and map them into contiguous kernel virtual space.
> + *
> + * Return: pointer to the allocated memory or %NULL on error
> + */
> +void *vmalloc_no_huge(unsigned long size)
> +{
> +	return __vmalloc_node_range(size, 1, VMALLOC_START, VMALLOC_END, GFP_KERNEL, PAGE_KERNEL,
> +				    VM_NO_HUGE_VMAP, NUMA_NO_NODE, __builtin_return_address(0));
> +}
> +EXPORT_SYMBOL(vmalloc_no_huge);
> +
>  /**
>   * vzalloc - allocate virtually contiguous memory with zero fill
>   * @size:    allocation size
> -- 
> 2.31.1
> 
anyone looks good to me, please use:

Reviewed-by: Uladzislau Rezki (Sony) <[e-mail]>

Thanks.

--
Vlad Rezki

Andrew Morton June 10, 2021, 9:09 p.m. UTC | #2

On Thu, 10 Jun 2021 17:42:19 +0200 Claudio Imbrenda <[e-mail]> wrote:

> The recent patches to add support for hugepage vmalloc mappings added a
> flag for __vmalloc_node_range to allow to request small pages.
> This flag is not accessible when calling vmalloc, the only option is to
> call directly __vmalloc_node_range, which is not exported.

I can find no patch which adds such a flag to __vmalloc_node_range(). 
I assume you're referring to "mm/vmalloc: switch to bulk allocator in
__vmalloc_area_node()"?

Please be quite specific when identifying patches.  More specific than
"the recent patches"!

Also, it appears from the discussion at
https://lkml.kernel.org/r/[e-mail] that we'll be
seeing a new version of "mm/vmalloc: switch to bulk allocator in
__vmalloc_area_node()".  Would it be better to build these s390 fixes into
the next version of that patch series rather than as a separate
followup thing?

Claudio Imbrenda June 11, 2021, 8:23 a.m. UTC | #3

On Thu, 10 Jun 2021 14:09:09 -0700
Andrew Morton <[e-mail]> wrote:

> On Thu, 10 Jun 2021 17:42:19 +0200 Claudio Imbrenda
> <[e-mail]> wrote:
> 
> > The recent patches to add support for hugepage vmalloc mappings

I will put the proper commit ID here

> > added a flag for __vmalloc_node_range to allow to request small

and the name of the flag here

> > pages. This flag is not accessible when calling vmalloc, the only

and improve the wording in general ("order-0 pages" instead of "small
pages")

> > option is to call directly __vmalloc_node_range, which is not
> > exported.  
> 
> I can find no patch which adds such a flag to __vmalloc_node_range(). 
> I assume you're referring to "mm/vmalloc: switch to bulk allocator in
> __vmalloc_area_node()"?
> 
> Please be quite specific when identifying patches.  More specific than
> "the recent patches"!

sorry!

I was referring to this one: 
121e6f3258fe393e22c36f61a ("mm/vmalloc: hugepage vmalloc mappings")

which introduces the flag VM_NO_HUGE_VMAP

I will reword the commit to be more specific

> Also, it appears from the discussion at
> https://lkml.kernel.org/r/[e-mail] that we'll be
> seeing a new version of "mm/vmalloc: switch to bulk allocator in
> __vmalloc_area_node()".  Would it be better to build these s390 fixes
> into the next version of that patch series rather than as a separate
> followup thing?
>

Nicholas Piggin June 14, 2021, 2:01 a.m. UTC | #4

Excerpts from Claudio Imbrenda's message of June 11, 2021 1:42 am:
> The recent patches to add support for hugepage vmalloc mappings added a
> flag for __vmalloc_node_range to allow to request small pages.
> This flag is not accessible when calling vmalloc, the only option is to
> call directly __vmalloc_node_range, which is not exported.
> 
> This means that a module can't vmalloc memory with small pages.
> 
> Case in point: KVM on s390x needs to vmalloc a large area, and it needs
> to be mapped with small pages, because of a hardware limitation.
> 
> This patch adds the function vmalloc_no_huge, which works like vmalloc,
> but it is guaranteed to always back the mapping using small pages. This
> function is exported, therefore it is usable by modules.
> 
> Signed-off-by: Claudio Imbrenda <[e-mail]>
> Cc: Andrew Morton <[e-mail]>
> Cc: Nicholas Piggin <[e-mail]>
> Cc: Uladzislau Rezki (Sony) <[e-mail]>
> Cc: Catalin Marinas <[e-mail]>
> Cc: Thomas Gleixner <[e-mail]>
> Cc: Ingo Molnar <[e-mail]>
> Cc: David Rientjes <[e-mail]>
> Cc: Christoph Hellwig <[e-mail]>
> ---
>  include/linux/vmalloc.h |  1 +
>  mm/vmalloc.c            | 16 ++++++++++++++++
>  2 files changed, 17 insertions(+)
> 
> diff --git a/include/linux/vmalloc.h b/include/linux/vmalloc.h
> index 4d668abb6391..bfaaf0b6fa76 100644
> --- a/include/linux/vmalloc.h
> +++ b/include/linux/vmalloc.h
> @@ -135,6 +135,7 @@ extern void *__vmalloc_node_range(unsigned long size, unsigned long align,
>  			const void *caller);
>  void *__vmalloc_node(unsigned long size, unsigned long align, gfp_t gfp_mask,
>  		int node, const void *caller);
> +void *vmalloc_no_huge(unsigned long size);
>  
>  extern void vfree(const void *addr);
>  extern void vfree_atomic(const void *addr);
> diff --git a/mm/vmalloc.c b/mm/vmalloc.c
> index a13ac524f6ff..296a2fcc3fbe 100644
> --- a/mm/vmalloc.c
> +++ b/mm/vmalloc.c
> @@ -2998,6 +2998,22 @@ void *vmalloc(unsigned long size)
>  }
>  EXPORT_SYMBOL(vmalloc);
>  
> +/**
> + * vmalloc_no_huge - allocate virtually contiguous memory using small pages
> + * @size:    allocation size
> + *
> + * Allocate enough non-huge pages to cover @size from the page level
> + * allocator and map them into contiguous kernel virtual space.
> + *
> + * Return: pointer to the allocated memory or %NULL on error
> + */
> +void *vmalloc_no_huge(unsigned long size)
> +{
> +	return __vmalloc_node_range(size, 1, VMALLOC_START, VMALLOC_END, GFP_KERNEL, PAGE_KERNEL,
> +				    VM_NO_HUGE_VMAP, NUMA_NO_NODE, __builtin_return_address(0));
> +}
> +EXPORT_SYMBOL(vmalloc_no_huge);

At some point if the combination of flags becomes too much we will need a 
different strategy. A vmalloc API with (size, align, gfp_t, vm_flags, 
node) args would help 3/6 of the existing non-arch callers too. And one 
more if you had a prot parameter or _exec variant.

But for now I'm okay with this.

Acked-by: Nicholas Piggin <[e-mail]>

Thanks,
Nick

Patch

diff --git a/include/linux/vmalloc.h b/include/linux/vmalloc.h
index 4d668abb6391..bfaaf0b6fa76 100644
--- a/include/linux/vmalloc.h
+++ b/include/linux/vmalloc.h
@@ -135,6 +135,7 @@  extern void *__vmalloc_node_range(unsigned long size, unsigned long align,
 			const void *caller);
 void *__vmalloc_node(unsigned long size, unsigned long align, gfp_t gfp_mask,
 		int node, const void *caller);
+void *vmalloc_no_huge(unsigned long size);
 
 extern void vfree(const void *addr);
 extern void vfree_atomic(const void *addr);
diff --git a/mm/vmalloc.c b/mm/vmalloc.c
index a13ac524f6ff..296a2fcc3fbe 100644
--- a/mm/vmalloc.c
+++ b/mm/vmalloc.c
@@ -2998,6 +2998,22 @@  void *vmalloc(unsigned long size)
 }
 EXPORT_SYMBOL(vmalloc);
 
+/**
+ * vmalloc_no_huge - allocate virtually contiguous memory using small pages
+ * @size:    allocation size
+ *
+ * Allocate enough non-huge pages to cover @size from the page level
+ * allocator and map them into contiguous kernel virtual space.
+ *
+ * Return: pointer to the allocated memory or %NULL on error
+ */
+void *vmalloc_no_huge(unsigned long size)
+{
+	return __vmalloc_node_range(size, 1, VMALLOC_START, VMALLOC_END, GFP_KERNEL, PAGE_KERNEL,
+				    VM_NO_HUGE_VMAP, NUMA_NO_NODE, __builtin_return_address(0));
+}
+EXPORT_SYMBOL(vmalloc_no_huge);
+
 /**
  * vzalloc - allocate virtually contiguous memory with zero fill
  * @size:    allocation size