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    SubjectRe: [PATCH v2 13/25] fs: Add zero_user_large
    On Tue, Feb 11, 2020 at 08:18:33PM -0800, Matthew Wilcox wrote:
    > From: "Matthew Wilcox (Oracle)" <willy@infradead.org>
    >
    > We can't kmap() a THP, so add a wrapper around zero_user() for large
    > pages.

    I would rather address it closer to the root: make zero_user_segments()
    handle compound pages.

    >
    > Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
    > ---
    > include/linux/highmem.h | 22 ++++++++++++++++++++++
    > 1 file changed, 22 insertions(+)
    >
    > diff --git a/include/linux/highmem.h b/include/linux/highmem.h
    > index ea5cdbd8c2c3..4465b8784353 100644
    > --- a/include/linux/highmem.h
    > +++ b/include/linux/highmem.h
    > @@ -245,6 +245,28 @@ static inline void zero_user(struct page *page,
    > zero_user_segments(page, start, start + size, 0, 0);
    > }
    >
    > +static inline void zero_user_large(struct page *page,
    > + unsigned start, unsigned size)
    > +{
    > + unsigned int i;
    > +
    > + for (i = 0; i < thp_order(page); i++) {
    > + if (start > PAGE_SIZE) {

    Off-by-one? >= ?

    > + start -= PAGE_SIZE;
    > + } else {
    > + unsigned this_size = size;
    > +
    > + if (size > (PAGE_SIZE - start))
    > + this_size = PAGE_SIZE - start;
    > + zero_user(page + i, start, this_size);
    > + start = 0;
    > + size -= this_size;
    > + if (!size)
    > + break;
    > + }
    > + }
    > +}
    > +
    > #ifndef __HAVE_ARCH_COPY_USER_HIGHPAGE
    >
    > static inline void copy_user_highpage(struct page *to, struct page *from,
    > --
    > 2.25.0
    >
    >

    --
    Kirill A. Shutemov

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