linux-kernel - Re: [RFC 1/3] mm/ksm: add anonymous check in find_mergeable

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Date: Wed, 5 Jun 2024 11:56:10 +0200
From: David Hildenbrand <david@...hat.com>
To: alexs@...nel.org, Andrew Morton <akpm@...ux-foundation.org>,
 linux-mm@...ck.org, linux-kernel@...r.kernel.org,
 izik.eidus@...ellosystems.com, willy@...radead.org, aarcange@...hat.com,
 chrisw@...s-sol.org, hughd@...gle.com
Subject: Re: [RFC 1/3] mm/ksm: add anonymous check in find_mergeable_vma

On 05.06.24 11:53, alexs@...nel.org wrote:
> From: "Alex Shi (tencent)" <alexs@...nel.org>
> 
> We do vma_set_anonyous in do_mmap(), and then vma_is_anonymous()
> checking workable, use it as a extra check since ksm only care anonymous
> pages.
> 
> Signed-off-by: Alex Shi (tencent) <alexs@...nel.org>
> ---
>   mm/ksm.c | 3 ++-
>   1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/mm/ksm.c b/mm/ksm.c
> index f5138f43f0d2..088bce39cd33 100644
> --- a/mm/ksm.c
> +++ b/mm/ksm.c
> @@ -742,7 +742,8 @@ static struct vm_area_struct *find_mergeable_vma(struct mm_struct *mm,
>   	if (ksm_test_exit(mm))
>   		return NULL;
>   	vma = vma_lookup(mm, addr);
> -	if (!vma || !(vma->vm_flags & VM_MERGEABLE) || !vma->anon_vma)
> +	if (!vma || !(vma->vm_flags & VM_MERGEABLE) || !vma->anon_vma ||
> +			!vma_is_anonymous(vma))

Doesn't KSM also apply to COW'ed pages in !anon mappings? At least 
that's what I recall.

-- 
Cheers,

David / dhildenb