linux-kernel - Re: [PATCH] mm: move dummy_vm

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Message-ID: <ZNBfEjZRWnPrCIGu@casper.infradead.org>
Date:   Mon, 7 Aug 2023 04:03:46 +0100
From:   Matthew Wilcox <willy@...radead.org>
To:     Mateusz Guzik <mjguzik@...il.com>
Cc:     akpm@...ux-foundation.org, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mm: move dummy_vm_ops out of a header

On Mon, Aug 07, 2023 at 01:16:11AM +0200, Mateusz Guzik wrote:
> Otherwise the kernel ends up with multiple copies:
> $ nm vmlinux | grep dummy_vm_ops
> ffffffff81e4ea00 d dummy_vm_ops.2
> ffffffff81e11760 d dummy_vm_ops.254
> ffffffff81e406e0 d dummy_vm_ops.4
> ffffffff81e3c780 d dummy_vm_ops.7
> 
> While here prefix it with vma_.

It really shouldn't be prefixed with vma.  Other than that, I love this
patch.

> [if someone has better ideas where to put it, please move it]
> 
> Signed-off-by: Mateusz Guzik <mjguzik@...il.com>
> ---
>  include/linux/mm.h | 6 +++---
>  mm/init-mm.c       | 2 ++
>  2 files changed, 5 insertions(+), 3 deletions(-)
> 
> diff --git a/include/linux/mm.h b/include/linux/mm.h
> index 406ab9ea818f..14898e76bbf1 100644
> --- a/include/linux/mm.h
> +++ b/include/linux/mm.h
> @@ -756,17 +756,17 @@ static inline void vma_mark_detached(struct vm_area_struct *vma,
>  
>  #endif /* CONFIG_PER_VMA_LOCK */
>  
> +extern const struct vm_operations_struct vma_dummy_vm_ops;
> +
>  /*
>   * WARNING: vma_init does not initialize vma->vm_lock.
>   * Use vm_area_alloc()/vm_area_free() if vma needs locking.
>   */
>  static inline void vma_init(struct vm_area_struct *vma, struct mm_struct *mm)
>  {
> -	static const struct vm_operations_struct dummy_vm_ops = {};
> -
>  	memset(vma, 0, sizeof(*vma));
>  	vma->vm_mm = mm;
> -	vma->vm_ops = &dummy_vm_ops;
> +	vma->vm_ops = &vma_dummy_vm_ops;
>  	INIT_LIST_HEAD(&vma->anon_vma_chain);
>  	vma_mark_detached(vma, false);
>  	vma_numab_state_init(vma);
> diff --git a/mm/init-mm.c b/mm/init-mm.c
> index efa97b57acfd..cfd367822cdd 100644
> --- a/mm/init-mm.c
> +++ b/mm/init-mm.c
> @@ -17,6 +17,8 @@
>  #define INIT_MM_CONTEXT(name)
>  #endif
>  
> +const struct vm_operations_struct vma_dummy_vm_ops;
> +
>  /*
>   * For dynamically allocated mm_structs, there is a dynamically sized cpumask
>   * at the end of the structure, the size of which depends on the maximum CPU
> -- 
> 2.39.2
> 
>