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Date:   Wed, 17 May 2023 15:58:04 +0100
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Subject: Re: [PATCH v3 2/3] mm: Call arch_swap_restore() from unuse_pte()
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To:     Peter Collingbourne <pcc@google.com>,
        Catalin Marinas <catalin.marinas@arm.com>
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        linux-mm@kvack.org, linux-kernel@vger.kernel.org,
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References: <20230517022115.3033604-1-pcc@google.com>
 <20230517022115.3033604-3-pcc@google.com>
From:   Steven Price <steven.price@arm.com>
In-Reply-To: <20230517022115.3033604-3-pcc@google.com>
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On 17/05/2023 03:21, Peter Collingbourne wrote:
> We would like to move away from requiring architectures to restore
> metadata from swap in the set_pte_at() implementation, as this is not only
> error-prone but adds complexity to the arch-specific code. This requires
> us to call arch_swap_restore() before calling swap_free() whenever pages
> are restored from swap. We are currently doing so everywhere except in
> unuse_pte(); do so there as well.
> 
> Signed-off-by: Peter Collingbourne <pcc@google.com>
> Link: https://linux-review.googlesource.com/id/I68276653e612d64cde271ce1b5a99ae05d6bbc4f

Reviewed-by: Steven Price <steven.price@arm.com>

> ---
>  mm/swapfile.c | 7 +++++++
>  1 file changed, 7 insertions(+)
> 
> diff --git a/mm/swapfile.c b/mm/swapfile.c
> index 274bbf797480..e9843fadecd6 100644
> --- a/mm/swapfile.c
> +++ b/mm/swapfile.c
> @@ -1794,6 +1794,13 @@ static int unuse_pte(struct vm_area_struct *vma, pmd_t *pmd,
>  		goto setpte;
>  	}
>  
> +	/*
> +	 * Some architectures may have to restore extra metadata to the page
> +	 * when reading from swap. This metadata may be indexed by swap entry
> +	 * so this must be called before swap_free().
> +	 */
> +	arch_swap_restore(entry, page_folio(page));
> +
>  	/* See do_swap_page() */
>  	BUG_ON(!PageAnon(page) && PageMappedToDisk(page));
>  	BUG_ON(PageAnon(page) && PageAnonExclusive(page));