From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from va-1-112.ptr.blmpb.com (va-1-112.ptr.blmpb.com [209.127.230.112]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 2BF313C060F for ; Wed, 1 Jul 2026 09:09:28 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.127.230.112 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1782896969; cv=none; b=iJun4FO7duLzDFFV00OHQpYaMxuddxJe1DWDcZhbvIkJ+xCXWmUyleprKB+cSN0mikE6cpgSf5jVkjP+uHudwlzwPhLjuRlGZzVJ0U/IHLyMthWMzkgXGiBDZp0h6tgP7nfKIAapmNXHsbKPCM42pq1qRso8887yBGs5qqEJAMs= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1782896969; c=relaxed/simple; bh=/FLdCG32++MJAY5z9lbhzw8lh2pbQxMOp+IfVl7XrKc=; h=In-Reply-To:Cc:From:Date:References:Subject:To:Message-Id: Mime-Version:Content-Type; b=FBb8k8f5HGDifJZnb3FMwXb7hw+sb4N9Gc0GFVUCrVYljutx0p4ypy9XOySayz1EHm04Z+rkRpyr/bIldPJ/z9WUocIV88hANj2F3ZcFJBNLAQXFLl8JQ5wHoj8HxJTezGBpHGfV9sW3LwRNeOLr7Z7I5Oqb1rTLHQyaIIFdv3I= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=bytedance.com; spf=pass smtp.mailfrom=bytedance.com; dkim=pass (2048-bit key) header.d=bytedance.com header.i=@bytedance.com header.b=Q1K7xKup; arc=none smtp.client-ip=209.127.230.112 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=bytedance.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=bytedance.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=bytedance.com header.i=@bytedance.com header.b="Q1K7xKup" DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; s=2212171451; d=bytedance.com; t=1782896964; h=from:subject: mime-version:from:date:message-id:subject:to:cc:reply-to:content-type: mime-version:in-reply-to:message-id; bh=EChoIRhSwBKjl45mE0KYtfQBcAG6r3vpLScAhY4aGho=; b=Q1K7xKupQgvsLGWwTJeT4z95PsQq+f0qhQs/5RFf+q+HMObCkLcVxWwSg8m/LX3hxbvBqI OOqXyVvh4GkwImqh1SjFXQEnROhT5WdEVxLUo5wo+aeJOJd6GaIeXkRGWG31uxZzJFepwC 9Z4fF/dJDnVVOGE68KhDW2M4HGU69mThyOZY8fyv8rKJ1ghPX+5TSCTfD45Yq6zw9nvwnz FIEWtdB2sLzqKIahJ9eBGwKCOrh66KTasj/tkp1HVhafMmxwMLvs/b5ngPrA1ZjL+nZAzi m0gRzPxBGVQH/RtgUd79U+DTmAeTC6pzSm1TAC+8c6dffaftVsK4XGuKB94UGw== In-Reply-To: <20260701090553.62691-1-lizhe.67@bytedance.com> Cc: , , , , , From: "Li Zhe" Date: Wed, 1 Jul 2026 17:05:51 +0800 References: <20260701090553.62691-1-lizhe.67@bytedance.com> X-Original-From: Li Zhe Subject: [PATCH v5 6/8] string: introduce memcpy_nt() helpers Content-Transfer-Encoding: 7bit To: , , , , , , , , , Message-Id: <20260701090553.62691-7-lizhe.67@bytedance.com> X-Mailer: git-send-email 2.45.2 Precedence: bulk X-Mailing-List: linux-arch@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 X-Lms-Return-Path: Content-Type: text/plain; charset=UTF-8 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 --- 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); +} + +static __always_inline void memcpy_nt_drain(void) +{ + asm volatile("sfence" : : : "memory"); +} #endif #endif /* __KERNEL__ */ diff --git a/include/linux/string.h b/include/linux/string.h index 5702daca4326..5165763ab812 100644 --- a/include/linux/string.h +++ b/include/linux/string.h @@ -278,6 +278,24 @@ static inline void memcpy_flushcache(void *dst, const void *src, size_t cnt) } #endif +#ifndef __HAVE_ARCH_MEMCPY_NT +/* + * memcpy_nt() requests a non-temporal copy when the architecture has a + * suitable backend. Callers must follow it with memcpy_nt_drain() + * before later normal stores that need to be ordered after the copy. + * Architectures that do not override it fall back to memcpy() and a + * no-op drain. + */ +static inline void memcpy_nt(void *dst, const void *src, size_t cnt) +{ + memcpy(dst, src, cnt); +} + +static inline void memcpy_nt_drain(void) +{ +} +#endif + void *memchr_inv(const void *s, int c, size_t n); char *strreplace(char *str, char old, char new); -- 2.20.1