Re: [PATCH v4 11/36] fs: Support THPs in zero_user_segments

Kirill A. Shutemov
2020-05-25T04:55:24Z

On Fri, May 15, 2020 at 06:16:31AM -0700, Matthew Wilcox wrote:
> From: "Matthew Wilcox (Oracle)" <willy@infradead.org>
>
> We can only kmap() one subpage of a THP at a time, so loop over all
> relevant subpages, skipping ones which don't need to be zeroed. This is
> too large to inline when THPs are enabled and we actually need highmem,
> so put it in highmem.c.
>
> Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
> ---
> include/linux/highmem.h | 15 +++++++---
> mm/highmem.c | 62 +++++++++++++++++++++++++++++++++++++++--
> 2 files changed, 71 insertions(+), 6 deletions(-)
>
> diff --git a/include/linux/highmem.h b/include/linux/highmem.h
> index ea5cdbd8c2c3..74614903619d 100644
> --- a/include/linux/highmem.h
> +++ b/include/linux/highmem.h
> @@ -215,13 +215,18 @@ static inline void clear_highpage(struct page *page)
> kunmap_atomic(kaddr);
> }
>
> +#if defined(CONFIG_HIGHMEM) && defined(CONFIG_TRANSPARENT_HUGEPAGE)
> +void zero_user_segments(struct page *page, unsigned start1, unsigned end1,
> + unsigned start2, unsigned end2);
> +#else /* !HIGHMEM || !TRANSPARENT_HUGEPAGE */
> static inline void zero_user_segments(struct page *page,
> - unsigned start1, unsigned end1,
> - unsigned start2, unsigned end2)
> + unsigned start1, unsigned end1,
> + unsigned start2, unsigned end2)
> {
> + unsigned long i;
> void *kaddr = kmap_atomic(page);
>
> - BUG_ON(end1 > PAGE_SIZE || end2 > PAGE_SIZE);
> + BUG_ON(end1 > thp_size(page) || end2 > thp_size(page));
>
> if (end1 > start1)
> memset(kaddr + start1, 0, end1 - start1);
> @@ -230,8 +235,10 @@ static inline void zero_user_segments(struct page *page,
> memset(kaddr + start2, 0, end2 - start2);
>
> kunmap_atomic(kaddr);
> - flush_dcache_page(page);
> + for (i = 0; i < hpage_nr_pages(page); i++)
> + flush_dcache_page(page + i);

Well, we need to settle on whether flush_dcache_page() has to be aware
about compound pages. There are already architectures that know how to
flush compound page, see ARM.

--
Kirill A. Shutemov