linux-kernel - Re: [PATCH v8 1/4] mm/vmalloc: allow to set node and align in vrealloc

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Message-ID: <aGJnXLl_OLqwjAUt@pc636>
Date: Mon, 30 Jun 2025 12:30:52 +0200
From: Uladzislau Rezki <urezki@...il.com>
To: Vitaly Wool <vitaly.wool@...sulko.se>
Cc: linux-mm@...ck.org, akpm@...ux-foundation.org,
	linux-kernel@...r.kernel.org, Uladzislau Rezki <urezki@...il.com>,
	Danilo Krummrich <dakr@...nel.org>,
	Alice Ryhl <aliceryhl@...gle.com>, rust-for-linux@...r.kernel.org
Subject: Re: [PATCH v8 1/4] mm/vmalloc: allow to set node and align in
 vrealloc

On Sat, Jun 28, 2025 at 12:25:37PM +0200, Vitaly Wool wrote:
> Reimplement vrealloc() to be able to set node and alignment should
> a user need to do so. Rename the function to vrealloc_node_align()
> to better match what it actually does now and introduce macros for
> vrealloc() and friends for backward compatibility.
> 
> With that change we also provide the ability for the Rust part of
> the kernel to set node and aligmnent in its allocations.
> 
> Signed-off-by: Vitaly Wool <vitaly.wool@...sulko.se>
> ---
>  include/linux/vmalloc.h | 12 +++++++++---
>  mm/vmalloc.c            | 20 ++++++++++++++++----
>  2 files changed, 25 insertions(+), 7 deletions(-)
> 
> diff --git a/include/linux/vmalloc.h b/include/linux/vmalloc.h
> index fdc9aeb74a44..68791f7cb3ba 100644
> --- a/include/linux/vmalloc.h
> +++ b/include/linux/vmalloc.h
> @@ -197,9 +197,15 @@ extern void *__vcalloc_noprof(size_t n, size_t size, gfp_t flags) __alloc_size(1
>  extern void *vcalloc_noprof(size_t n, size_t size) __alloc_size(1, 2);
>  #define vcalloc(...)		alloc_hooks(vcalloc_noprof(__VA_ARGS__))
>  
> -void * __must_check vrealloc_noprof(const void *p, size_t size, gfp_t flags)
> -		__realloc_size(2);
> -#define vrealloc(...)		alloc_hooks(vrealloc_noprof(__VA_ARGS__))
> +void *__must_check vrealloc_node_align_noprof(const void *p, size_t size,
> +		unsigned long align, gfp_t flags, int nid) __realloc_size(2);
> +#define vrealloc_node_noprof(_p, _s, _f, _nid)	\
> +	vrealloc_node_align_noprof(_p, _s, 1, _f, _nid)
> +#define vrealloc_noprof(_p, _s, _f)		\
> +	vrealloc_node_align_noprof(_p, _s, 1, _f, NUMA_NO_NODE)
> +#define vrealloc_node_align(...)		alloc_hooks(vrealloc_node_align_noprof(__VA_ARGS__))
> +#define vrealloc_node(...)			alloc_hooks(vrealloc_node_noprof(__VA_ARGS__))
> +#define vrealloc(...)				alloc_hooks(vrealloc_noprof(__VA_ARGS__))
>  
>  extern void vfree(const void *addr);
>  extern void vfree_atomic(const void *addr);
> diff --git a/mm/vmalloc.c b/mm/vmalloc.c
> index 6dbcdceecae1..d633ac0ff977 100644
> --- a/mm/vmalloc.c
> +++ b/mm/vmalloc.c
> @@ -4089,12 +4089,15 @@ void *vzalloc_node_noprof(unsigned long size, int node)
>  EXPORT_SYMBOL(vzalloc_node_noprof);
>  
>  /**
> - * vrealloc - reallocate virtually contiguous memory; contents remain unchanged
> + * vrealloc_node_align_noprof - reallocate virtually contiguous memory; contents
> + * remain unchanged
>   * @p: object to reallocate memory for
>   * @size: the size to reallocate
> + * @align: requested alignment
>   * @flags: the flags for the page level allocator
> + * @nid: node id
>   *
> - * If @p is %NULL, vrealloc() behaves exactly like vmalloc(). If @size is 0 and
> + * If @p is %NULL, vrealloc_XXX() behaves exactly like vmalloc(). If @size is 0 and
>   * @p is not a %NULL pointer, the object pointed to is freed.
>   *
>   * If __GFP_ZERO logic is requested, callers must ensure that, starting with the
> @@ -4111,7 +4114,8 @@ EXPORT_SYMBOL(vzalloc_node_noprof);
>   * Return: pointer to the allocated memory; %NULL if @size is zero or in case of
>   *         failure
>   */
> -void *vrealloc_noprof(const void *p, size_t size, gfp_t flags)
> +void *vrealloc_node_align_noprof(const void *p, size_t size, unsigned long align,
> +				 gfp_t flags, int nid)
>  {
>  	struct vm_struct *vm = NULL;
>  	size_t alloced_size = 0;
> @@ -4135,6 +4139,13 @@ void *vrealloc_noprof(const void *p, size_t size, gfp_t flags)
>  		if (WARN(alloced_size < old_size,
>  			 "vrealloc() has mismatched area vs requested sizes (%p)\n", p))
>  			return NULL;
> +		if (WARN(nid != NUMA_NO_NODE && nid != page_to_nid(vmalloc_to_page(p)),
> +			 "vrealloc() has mismatched nids\n"))
> +			return NULL;
> +		if (WARN((uintptr_t)p & (align - 1),
> +			 "will not reallocate with a bigger alignment (0x%lx)\n",
> +			 align))
> +			return NULL;
>
IMO, IS_ALIGNED() should be used instead. We have already a macro for this
purpose, i.e. the idea is just to check that "p" is aligned with "align"
request.

Can you replace the (uintptr_t) casting to (ulong) or (unsigned long)
this is how we mostly cast in vmalloc code?

WARN() probably is worth to replace. Use WARN_ON_ONCE() to prevent
flooding.

--
Uladzislau Rezki