From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mgamail.intel.com (mgamail.intel.com [198.175.65.16]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 0929E33C1B7; Sat, 29 Aug 2026 04:41:10 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=198.175.65.16 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1787978474; cv=none; b=PAOuEiUMhOgeIedTWIjbThSUb+ygOrknJmyR4WyhwcQPqAddmmQUsLpvkWVT2PN/IUSnvOtJzb4wMTz4ZN34s7aO8yp4vQwwFuHMRU8slC/Qg4Ul/sLIbq0a4no9nI/xTryjx0ynUvjc2LFNW1/rgjiGW+WrMhQH/ms+WCVIL+I= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1787978474; c=relaxed/simple; bh=2JGqXWCbZ5rvViDhEt7kOXZr99HBUzTG6/6Uyla+htg=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=Cj5aGmloHmN/6PU8aJZ17hyVkrSKM65z1N6E+hKJftlJniZ72m/aoJCA+SUpFX+2jKLI05TNKycQXDJiNWUzjBlUwfezRTVaYlpUhHydPezHABwwxlvZFypmdgmWMBhrPQFpYAOk2+vC5kkIqvrJhdAORF45kYQqju6M2i1d22s= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=intel.com; spf=pass smtp.mailfrom=intel.com; dkim=pass (2048-bit key) header.d=intel.com header.i=@intel.com header.b=LZMX4/ra; arc=none smtp.client-ip=198.175.65.16 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=intel.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=intel.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=intel.com header.i=@intel.com header.b="LZMX4/ra" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=intel.com; i=@intel.com; q=dns/txt; s=Intel; t=1787978471; x=1819514471; h=from:to:cc:subject:date:message-id:in-reply-to: references:mime-version:content-transfer-encoding; bh=2JGqXWCbZ5rvViDhEt7kOXZr99HBUzTG6/6Uyla+htg=; b=LZMX4/ra7zlIiDTXvUL8EDBB1AIVNmrYjSB4zuupJf1N0cHTv4ueokJ9 ENKAi10cuNhhgFy1MxxKLQlnx1dry03gQDjrPXwpw3v0OTTufcdAdIUv5 NsMmbAFo9erEw0sJFBgD7o14YGPMDUBlbDlyrzbG4Rcseq6iW8xAtDs4Z WmmIcusmvF9pOvGDorNv9jkQHmm9rn5wy9mKVbyq47eTXTDRprqMbSndX eUn31+eUirC4/pRfhmrmWlzf+nGj92z8z+IoOz6RcDMA6fYQmDUk7g3+N sq+U6HlKiEF5LJahCfKVaaRtguswYCJOxPRPfwjyvyvO7mZpG7+k/2Tb1 g==; X-CSE-ConnectionGUID: ciAfApalQ3ikRsELkbHFqQ== X-CSE-MsgGUID: X4XMPynRQPa9ZQ/DCjtQFw== X-IronPort-AV: E=McAfee;i="6800,10657,11889"; a="88683935" X-IronPort-AV: E=Sophos;i="6.25,249,1779174000"; d="scan'208";a="88683935" Received: from orviesa006.jf.intel.com ([10.64.159.146]) by orvoesa108.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 28 Aug 2026 21:41:11 -0700 X-CSE-ConnectionGUID: PVdNb1TbTG6lMhgtjoogew== X-CSE-MsgGUID: MsJFC2WfSh6fGBC2zTN5zQ== X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="6.25,249,1779174000"; d="scan'208";a="266533038" Received: from pankris-x299-ud4-pro.bj.intel.com ([10.238.152.122]) by orviesa006.jf.intel.com with ESMTP; 28 Aug 2026 21:41:08 -0700 From: Kris Pan To: gregkh@linuxfoundation.org Cc: akpm@linux-foundation.org, hughd@google.com, viro@zeniv.linux.org.uk, brauner@kernel.org, arnd@arndb.de, max.kellermann@ionos.com, linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, Kris Pan Subject: [PATCH v2 2/2] drivers/char/mem: splice the zero page for /dev/zero and /dev/full Date: Sat, 29 Aug 2026 12:37:46 +0800 Message-ID: <20260829043746.2929210-3-kris.pan@intel.com> X-Mailer: git-send-email 2.43.0 In-Reply-To: <20260829043746.2929210-1-kris.pan@intel.com> References: <20260829043746.2929210-1-kris.pan@intel.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Implement a splice_read handler for /dev/zero and /dev/full that pushes references to the global zero page into the pipe, instead of allocating and zeroing a fresh page for every pipe buffer. This is much faster than copy_splice_read() for splicing zeroes, since it avoids the page allocation and zeroing on every pipe buffer. Use the shared splice_zeropage_into_pipe() helper from fs/splice.c. Signed-off-by: Kris Pan Reviewed-by: Max Kellermann --- drivers/char/mem.c | 29 +++++++++++++++++++++++++++-- 1 file changed, 27 insertions(+), 2 deletions(-) diff --git a/drivers/char/mem.c b/drivers/char/mem.c index 63253d1de5d70..6d3ef359b2d7b 100644 --- a/drivers/char/mem.c +++ b/drivers/char/mem.c @@ -471,6 +471,31 @@ static ssize_t read_iter_zero(struct kiocb *iocb, struct iov_iter *iter) return written; } +static ssize_t splice_read_zero(struct file *in, loff_t *ppos, + struct pipe_inode_info *pipe, size_t len, + unsigned int flags) +{ + size_t total = 0; + loff_t pos = 0; + size_t used, npages; + + used = pipe_buf_usage(pipe); + if (used >= pipe->max_usage) + return -EAGAIN; + npages = pipe->max_usage - used; + len = min_t(size_t, len, npages * PAGE_SIZE); + + while (len) { + size_t n = splice_zeropage_into_pipe(pipe, pos, len); + + pos += n; + total += n; + len -= n; + } + + return total; +} + static ssize_t read_zero(struct file *file, char __user *buf, size_t count, loff_t *ppos) { @@ -669,7 +694,7 @@ static const struct file_operations zero_fops = { .read_iter = read_iter_zero, .read = read_zero, .write_iter = write_iter_zero, - .splice_read = copy_splice_read, + .splice_read = splice_read_zero, .splice_write = splice_write_zero, .mmap_prepare = mmap_zero_prepare, .get_unmapped_area = get_unmapped_area_zero, @@ -682,7 +707,7 @@ static const struct file_operations full_fops = { .llseek = full_lseek, .read_iter = read_iter_zero, .write = write_full, - .splice_read = copy_splice_read, + .splice_read = splice_read_zero, }; static const struct memdev { -- 2.43.0