On Wed, Jul 01, 2026 at 05:05:52PM +0800, Li Zhe wrote: > The new x86 memcpy_nt() helper in this series maps to > memcpy_flushcache(), and the ZONE_DEVICE fast path uses that primitive > for constant-sized struct page template copies. > > memcpy_flushcache() currently inlines only the 4, 8, and 16-byte > cases. Larger constant-sized copies fall back to __memcpy_flushcache() > even when the destination is naturally aligned. Extend the inline > movnti coverage to 32, 48, 64, 80, and 96 bytes so the struct
Why exactly those sizes and not bigger? Any numbers to back this up? > page-sized copies used by that path can stay on the inline > non-temporal store path instead of dropping into the out-of-line > helper. > > Factor the store sequences into 8/16/32/64-byte helpers, keep the > existing 4/8/16-byte cases handled directly in memcpy_flushcache(), > issue the stores in ascending address order, and leave all other sizes > on __memcpy_flushcache(). > > Signed-off-by: Li Zhe <[email protected]> > --- > arch/x86/include/asm/string_64.h | 80 +++++++++++++++++++++++++++++++- > 1 file changed, 79 insertions(+), 1 deletion(-) > > diff --git a/arch/x86/include/asm/string_64.h > b/arch/x86/include/asm/string_64.h > index 6f36abedc56a..95ef2d481418 100644 > --- a/arch/x86/include/asm/string_64.h > +++ b/arch/x86/include/asm/string_64.h > @@ -4,6 +4,7 @@ > > #ifdef __KERNEL__ > #include <linux/jump_label.h> > +#include <linux/align.h> > > /* Written 2002 by Andi Kleen */ > > @@ -82,8 +83,81 @@ int strcmp(const char *cs, const char *ct); > #ifdef CONFIG_ARCH_HAS_UACCESS_FLUSHCACHE > #define __HAVE_ARCH_MEMCPY_FLUSHCACHE 1 > void __memcpy_flushcache(void *dst, const void *src, size_t cnt); > -static __always_inline void memcpy_flushcache(void *dst, const void *src, > size_t cnt) > + > +static __always_inline void memcpy_flushcache_8(void *dst, const void *src) If this is calling MOVNTI, you might as well call it that way. Only leave the externally exposed wrapper called "flushcache". > +{ > + asm volatile("movntiq %1, %0" > + : "=m"(*(u64 *)dst) > + : "r"(*(const u64 *)src) > + : "memory"); > +} > + > +static __always_inline void memcpy_flushcache_16(void *dst, > + const void *src) > +{ > + memcpy_flushcache_8(dst, src); > + memcpy_flushcache_8(dst + 8, src + 8); > +} > + > +static __always_inline void memcpy_flushcache_32(void *dst, > + const void *src) > +{ > + memcpy_flushcache_16(dst, src); > + memcpy_flushcache_16(dst + 16, src + 16); > +} > + > +static __always_inline void memcpy_flushcache_64(void *dst, > + const void *src) > { > + memcpy_flushcache_32(dst, src); > + memcpy_flushcache_32(dst + 32, src + 32); > +} > + > +/* > + * Keep the additional aligned fixed-size cases on the inline movnti path. > + * Leave the existing 4/8/16-byte cases handled directly in > + * memcpy_flushcache() so their code generation stays unchanged. > + */ > +static __always_inline int memcpy_flushcache_large(void *dst, > + const void *src, > + size_t cnt) > +{ > + char *dptr = dst; > + const char *sptr = src; > + > + if (!IS_ALIGNED((unsigned long)dst, 8)) > + return 0; > + > + switch (cnt) { > + case 32: > + memcpy_flushcache_32(dptr, sptr); > + return 1; > + case 48: > + memcpy_flushcache_32(dptr, sptr); > + memcpy_flushcache_16(dptr + 32, sptr + 32); > + return 1; > + case 64: > + memcpy_flushcache_64(dptr, sptr); > + return 1; > + case 80: > + memcpy_flushcache_64(dptr, sptr); > + memcpy_flushcache_16(dptr + 64, sptr + 64); > + return 1; > + case 96: > + memcpy_flushcache_64(dptr, sptr); > + memcpy_flushcache_32(dptr + 64, sptr + 64); > + return 1; > + } > + > + return 0; > +} > + > +static __always_inline void memcpy_flushcache(void *dst, const void *src, > + size_t cnt) > +{ > + if (!cnt) > + return; > + > if (__builtin_constant_p(cnt)) { > switch (cnt) { > case 4: > @@ -97,7 +171,11 @@ static __always_inline void memcpy_flushcache(void *dst, > const void *src, size_t > asm ("movntiq %1, %0" : "=m"(*(u64 *)(dst + 8)) > : "r"(*(u64 *)(src + 8))); > return; > } > + > + if (memcpy_flushcache_large(dst, src, cnt)) Why is this a separate function and not extending the switch-case? I betcha it has to do with the alignment check but nothing explains to me why. -- Regards/Gruss, Boris. https://people.kernel.org/tglx/notes-about-netiquette
