linux-kernel - Re: [PATCH v2] vma remove the unneeded avc bound with non-CoWed folio

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Message-ID: <2f19c2ff-66b2-4860-a870-a1bffe73320c@redhat.com>
Date: Mon, 26 Aug 2024 19:24:45 +0200
From: David Hildenbrand <david@...hat.com>
To: Zhiguo Jiang <justinjiang@...o.com>,
 Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
 linux-kernel@...r.kernel.org, oe-lkp@...ts.linux.dev, oliver.sang@...el.com
Cc: opensource.kernel@...o.com
Subject: Re: [PATCH v2] vma remove the unneeded avc bound with non-CoWed folio

On 23.08.24 16:01, Zhiguo Jiang wrote:
> After CoWed by do_wp_page, the vma established a new mapping relationship
> with the CoWed folio instead of the non-CoWed folio. However, regarding
> the situation where vma->anon_vma and the non-CoWed folio's anon_vma are
> not same, the avc binding relationship between them will no longer be
> needed, so it is issue for the avc binding relationship still existing
> between them.
> 
> This patch will remove the avc binding relationship between vma and the
> non-CoWed folio's anon_vma, which each has their own independent
> anon_vma. It can also alleviates rmap overhead simultaneously.
> 
> Signed-off-by: Zhiguo Jiang <justinjiang@...o.com>
> ---
> -v2:
>   * Solve the kernel test robot noticed "WARNING"
>     Reported-by: kernel test robot <oliver.sang@...el.com>
>     Closes: https://lore.kernel.org/oe-lkp/202408230938.43f55b4-lkp@intel.com
>   * Update comments to more accurately describe this patch.
> 
> -v1:
>   https://lore.kernel.org/linux-mm/20240820143359.199-1-justinjiang@vivo.com/
> 
>   include/linux/rmap.h |  1 +
>   mm/memory.c          |  8 +++++++
>   mm/rmap.c            | 53 ++++++++++++++++++++++++++++++++++++++++++++
>   3 files changed, 62 insertions(+)
> 
> diff --git a/include/linux/rmap.h b/include/linux/rmap.h
> index 91b5935e8485..8607d28a3146
> --- a/include/linux/rmap.h
> +++ b/include/linux/rmap.h
> @@ -257,6 +257,7 @@ void folio_remove_rmap_ptes(struct folio *, struct page *, int nr_pages,
>   	folio_remove_rmap_ptes(folio, page, 1, vma)
>   void folio_remove_rmap_pmd(struct folio *, struct page *,
>   		struct vm_area_struct *);
> +void folio_remove_anon_avc(struct folio *, struct vm_area_struct *);
>   
>   void hugetlb_add_anon_rmap(struct folio *, struct vm_area_struct *,
>   		unsigned long address, rmap_t flags);
> diff --git a/mm/memory.c b/mm/memory.c
> index 93c0c25433d0..4c89cb1cb73e
> --- a/mm/memory.c
> +++ b/mm/memory.c
> @@ -3428,6 +3428,14 @@ static vm_fault_t wp_page_copy(struct vm_fault *vmf)
>   			 * old page will be flushed before it can be reused.
>   			 */
>   			folio_remove_rmap_pte(old_folio, vmf->page, vma);
> +
> +			/*
> +			 * If the new_folio's anon_vma is different from the
> +			 * old_folio's anon_vma, the avc binding relationship
> +			 * between vma and the old_folio's anon_vma is removed,
> +			 * avoiding rmap redundant overhead.
> +			 */
> +			folio_remove_anon_avc(old_folio, vma);

... by increasing write fault latency, introducing an RMAP walk (!)? Hmm?

On the reuse path, we do a folio_move_anon_rmap(), to optimize that.

-- 
Cheers,

David / dhildenb