On 7/1/26 11:05, Li Zhe wrote: > Introduce memcpy_nt() and memcpy_nt_drain() for write-once copy sites > that want a named non-temporal copy primitive plus an explicit ordering > point. On x86, place the arch-visible wrapper in > arch/x86/include/asm/string_64.h and map it to the existing > memcpy_flushcache() backend plus sfence. Architectures that do not > override the helper fall back to memcpy() and a no-op drain in > include/linux/string.h. > > The immediate user is the ZONE_DEVICE template-copy path. That path > populates struct page descriptors in a write-once pattern, so most > destination cachelines are not expected to be reused immediately after > the copy. A regular cached memcpy() can therefore incur avoidable > write-allocate traffic and pollute the cache with data that has little > near-term reuse. > > This interface lets callers request that non-temporal-copy semantics > directly, while x86 simply reuses the existing memcpy_flushcache() > backend instead of adding another generic memcpy-like wrapper with > extra selection policy above it. > > Signed-off-by: Li Zhe <[email protected]> > --- > arch/x86/include/asm/string_64.h | 16 ++++++++++++++++ > include/linux/string.h | 18 ++++++++++++++++++ > 2 files changed, 34 insertions(+) > > diff --git a/arch/x86/include/asm/string_64.h > b/arch/x86/include/asm/string_64.h > index 4635616863f5..6f36abedc56a 100644 > --- a/arch/x86/include/asm/string_64.h > +++ b/arch/x86/include/asm/string_64.h > @@ -100,6 +100,22 @@ static __always_inline void memcpy_flushcache(void *dst, > const void *src, size_t > } > __memcpy_flushcache(dst, src, cnt); > } > + > +#define __HAVE_ARCH_MEMCPY_NT 1 > +/* > + * Reuse the existing x86 flushcache backend as the nt copy primitive. > + * Callers pair it with memcpy_nt_drain() when later stores must be > + * ordered after the copy. > + */ > +static __always_inline void memcpy_nt(void *dst, const void *src, size_t cnt) > +{ > + memcpy_flushcache(dst, src, cnt); > +}
In particular if you end up with a single function (that jsut requires a write memory barrier afterwards), please make this #define memcpy_nt memcpy_nt instead. -- Cheers, David
