linux-kernel - Re: [PATCH v2 2/4] mm: ksm: refer to special VMAs via VM_SPECIAL in ksm

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Message-ID: <iekjqr3hb2kshtsq5jvn3xtsgwnvxycfuybl6tp32ciwsb7wfx@mpqqd5vzxvmm>
Date: Mon, 26 May 2025 10:31:30 -0400
From: "Liam R. Howlett" <Liam.Howlett@...cle.com>
To: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
Cc: Andrew Morton <akpm@...ux-foundation.org>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        Christian Brauner <brauner@...nel.org>, Jan Kara <jack@...e.cz>,
        Vlastimil Babka <vbabka@...e.cz>, Jann Horn <jannh@...gle.com>,
        Pedro Falcato <pfalcato@...e.de>, David Hildenbrand <david@...hat.com>,
        Xu Xin <xu.xin16@....com.cn>,
        Chengming Zhou <chengming.zhou@...ux.dev>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        Stefan Roesch <shr@...kernel.io>
Subject: Re: [PATCH v2 2/4] mm: ksm: refer to special VMAs via VM_SPECIAL in
 ksm_compatible()

* Lorenzo Stoakes <lorenzo.stoakes@...cle.com> [250521 14:20]:
> There's no need to spell out all the special cases, also doing it this way
> makes it absolutely clear that we preclude unmergeable VMAs in general, and
> puts the other excluded flags in stark and clear contrast.
> 
> Signed-off-by: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
> Acked-by: David Hildenbrand <david@...hat.com>
> Reviewed-by: Chengming Zhou <chengming.zhou@...ux.dev>

Reviewed-by: Liam R. Howlett <Liam.Howlett@...cle.com>

> ---
>  mm/ksm.c | 5 ++---
>  1 file changed, 2 insertions(+), 3 deletions(-)
> 
> diff --git a/mm/ksm.c b/mm/ksm.c
> index 08d486f188ff..d0c763abd499 100644
> --- a/mm/ksm.c
> +++ b/mm/ksm.c
> @@ -679,9 +679,8 @@ static int break_ksm(struct vm_area_struct *vma, unsigned long addr, bool lock_v
>  
>  static bool ksm_compatible(const struct file *file, vm_flags_t vm_flags)
>  {
> -	if (vm_flags & (VM_SHARED   | VM_MAYSHARE   | VM_PFNMAP  |
> -			VM_IO       | VM_DONTEXPAND | VM_HUGETLB |
> -			VM_MIXEDMAP | VM_DROPPABLE))
> +	if (vm_flags & (VM_SHARED  | VM_MAYSHARE | VM_SPECIAL |
> +			VM_HUGETLB | VM_DROPPABLE))
>  		return false;		/* just ignore the advice */
>  
>  	if (file_is_dax(file))
> -- 
> 2.49.0
>