On Wed, Oct 26, 2016 at 10:50:20AM -0500, Brian Boylston wrote:
> Update copy_from_iter_nocache() to use memcpy_nocache()
> for bvecs and kvecs.
>
> Cc: Ross Zwisler
> Cc: Thomas Gleixner
> Cc: Ingo Molnar
> Cc: "H. Peter Anvin"
> Cc:
> Cc: Al Viro
> Cc: Dan Williams
> Signed-off-by: Brian Boylston
> Reviewed-by: Toshi Kani
> Reported-by: Oliver Moreno
> ---
> lib/iov_iter.c | 14 +++---
> 1 file changed, 11 insertions(+), 3 deletions(-)
>
> diff --git a/lib/iov_iter.c b/lib/iov_iter.c
> index 7e3138c..71e4531 100644
> --- a/lib/iov_iter.c
> +++ b/lib/iov_iter.c
> @@ -342,6 +342,13 @@ static void memcpy_from_page(char *to, struct page
> *page, size_t offset, size_t
> kunmap_atomic(from);
> }
>
> +static void memcpy_from_page_nocache(char *to, struct page *page, size_t
> offset, size_t len)
> +{
> + char *from = kmap_atomic(page);
> + memcpy_nocache(to, from + offset, len);
> + kunmap_atomic(from);
> +}
> +
> static void memcpy_to_page(struct page *page, size_t offset, const char
> *from, size_t len)
> {
> char *to = kmap_atomic(page);
> @@ -392,9 +399,10 @@ size_t copy_from_iter_nocache(void *addr, size_t bytes,
> struct iov_iter *i)
> iterate_and_advance(i, bytes, v,
> __copy_from_user_nocache((to += v.iov_len) - v.iov_len,
>v.iov_base, v.iov_len),
> - memcpy_from_page((to += v.bv_len) - v.bv_len, v.bv_page,
> - v.bv_offset, v.bv_len),
> - memcpy((to += v.iov_len) - v.iov_len, v.iov_base, v.iov_len)
> + memcpy_from_page_nocache((to += v.bv_len) - v.bv_len,
> + v.bv_page, v.bv_offset, v.bv_len),
> + memcpy_nocache((to += v.iov_len) - v.iov_len,
> +v.iov_base, v.iov_len)
> )
>
> return bytes;
> --
> 2.8.3
I generally agree with Boaz's comments to your patch 1 - this feels like yet
another layer where we have indirection based on the architecture.
We already have an arch switch at memcpy_to_pmem() based on whether the
architecture supports the PMEM API. And we already have
__copy_from_user_nocache(), which based on the architecture can map to either
a non-cached memcpy (x86_32, x86_64), or it can just map to a normal memcpy
via __copy_from_user_inatomic() (this happens in include/linux/uaccss.h, which
I believe is used for all non-x86 architectures).
memcpy_nocache() now does the same thing as __copy_from_user_nocache(), where
we define an uncached memcpy for x86_32 and x86_64, and a normal memcpy
variant for other architectures. But, weirdly, the x86 version maps to our
to __copy_from_user_nocache(), but it on non-x86 we don't map to
__copy_from_user_nocache() and use its fallback, we provide a new fallback of
our own via a direct call to memcpy()?
And, now in copy_from_iter_nocache() on x86 we call __copy_from_user_nocache()
two different ways: directly, and indirectly through memcpy_nocache() and
memcpy_from_page_nocache()=>memcpy_nocache().
Is there any way to simplify all of this?
All in all I'm on board with doing non-temporal copies in all cases, and I
like the idea behind memcpy_from_page_nocache(). I just think there must be a
way to make it simpler.
