linux-ext4 - Re: [PATCH 1/7] highmem: Add memcpy_to_folio() and memcpy_from

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Date:   Sat, 22 Jul 2023 02:06:50 +0200
From:   Andreas Grünbacher <andreas.gruenbacher@...il.com>
To:     "Matthew Wilcox (Oracle)" <willy@...radead.org>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        David Sterba <dsterba@...e.com>, linux-fsdevel@...r.kernel.org,
        Pankaj Raghav <p.raghav@...sung.com>,
        Konstantin Komarov <almaz.alexandrovich@...agon-software.com>,
        ntfs3@...ts.linux.dev, Theodore Tso <tytso@....edu>,
        Jan Kara <jack@...e.com>, linux-ext4@...r.kernel.org
Subject: Re: [PATCH 1/7] highmem: Add memcpy_to_folio() and memcpy_from_folio()

Am Do., 13. Juli 2023 um 06:04 Uhr schrieb Matthew Wilcox (Oracle)
<willy@...radead.org>:
> These are the folio equivalent of memcpy_to_page() and memcpy_from_page().
>
> Signed-off-by: Matthew Wilcox (Oracle) <willy@...radead.org>
> ---
>  include/linux/highmem.h | 44 +++++++++++++++++++++++++++++++++++++++++
>  1 file changed, 44 insertions(+)
>
> diff --git a/include/linux/highmem.h b/include/linux/highmem.h
> index 68da30625a6c..0280f57d4744 100644
> --- a/include/linux/highmem.h
> +++ b/include/linux/highmem.h
> @@ -439,6 +439,50 @@ static inline void memzero_page(struct page *page, size_t offset, size_t len)
>         kunmap_local(addr);
>  }
>
> +static inline void memcpy_from_folio(char *to, struct folio *folio,
> +               size_t offset, size_t len)
> +{
> +       VM_BUG_ON(offset + len > folio_size(folio));
> +
> +       do {
> +               char *from = kmap_local_folio(folio, offset);
> +               size_t chunk = len;
> +
> +               if (folio_test_highmem(folio) &&
> +                   (chunk > (PAGE_SIZE - offset_in_page(offset))))
> +                       chunk = PAGE_SIZE - offset_in_page(offset);
> +               memcpy(to, from, len);

We want memcpy(to, from, chunk) here.

> +               kunmap_local(from);
> +
> +               from += chunk;
> +               offset += chunk;
> +               len -= chunk;
> +       } while (len > 0);
> +}
> +
> +static inline void memcpy_to_folio(struct folio *folio, size_t offset,
> +               const char *from, size_t len)
> +{
> +       VM_BUG_ON(offset + len > folio_size(folio));
> +
> +       do {
> +               char *to = kmap_local_folio(folio, offset);
> +               size_t chunk = len;
> +
> +               if (folio_test_highmem(folio) &&
> +                   (chunk > (PAGE_SIZE - offset_in_page(offset))))
> +                       chunk = PAGE_SIZE - offset_in_page(offset);
> +               memcpy(to, from, len);

And also here.

> +               kunmap_local(to);
> +
> +               from += chunk;
> +               offset += chunk;
> +               len -= chunk;
> +       } while (len > 0);
> +
> +       flush_dcache_folio(folio);
> +}
> +
>  /**
>   * memcpy_from_file_folio - Copy some bytes from a file folio.
>   * @to: The destination buffer.
> --
> 2.39.2
>

Thanks,
Andreas