linux-kernel - Re: [PATCH v3 2/3] mm: Call arch_swap_restore() from unuse

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Date:   Wed, 17 May 2023 10:37:28 +0200
From:   David Hildenbrand <david@...hat.com>
To:     Peter Collingbourne <pcc@...gle.com>,
        Catalin Marinas <catalin.marinas@....com>
Cc:     Qun-wei Lin (林群崴) 
        <Qun-wei.Lin@...iatek.com>, linux-arm-kernel@...ts.infradead.org,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        "surenb@...gle.com" <surenb@...gle.com>,
        Chinwen Chang (張錦文) 
        <chinwen.chang@...iatek.com>,
        "kasan-dev@...glegroups.com" <kasan-dev@...glegroups.com>,
        Kuan-Ying Lee (李冠穎) 
        <Kuan-Ying.Lee@...iatek.com>,
        Casper Li (李中榮) <casper.li@...iatek.com>,
        "gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
        vincenzo.frascino@....com,
        Alexandru Elisei <alexandru.elisei@....com>, will@...nel.org,
        eugenis@...gle.com, Steven Price <steven.price@....com>
Subject: Re: [PATCH v3 2/3] mm: Call arch_swap_restore() from unuse_pte()

On 17.05.23 04:21, 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@...gle.com>
> Link: https://linux-review.googlesource.com/id/I68276653e612d64cde271ce1b5a99ae05d6bbc4f
> ---
>   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));

Acked-by: David Hildenbrand <david@...hat.com>

-- 
Thanks,

David / dhildenb