From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mgamail.intel.com (mgamail.intel.com [192.198.163.15]) (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 4BD12632; Sun, 16 Jun 2024 04:01:15 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=192.198.163.15 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1718510476; cv=none; b=ZlE/jv2nW4w0UN26cHLVDrJjynpSerbG3/yPgNWMRCagAiK9XtA62b0biygwq/9PNPG07QJ9pVagL9bOWkcUSpWv/d/n/4HAIst3WBWZK4/vQQ9gQrX03zkkBdMcwlMeCEx3jk0GhQ/8f8N0mslVQrJ/ndaDVcDAZlYvLHKcmjQ= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1718510476; c=relaxed/simple; bh=LOBeSDMLvjOcAiROl79GUg1b1Ol44rfsv4ROT9gOiwM=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=jlcLLCoZObs8dg2mH8DV/RHKYiOdzzazHWuAMAjh5j2EcMK+JQDqEfous06KCfh9o3yg833BZDl2MXAuQNTPHKvlDzfV6OYX4CcPiXHZ21nX6FwzMp7y4YAZ0NZWIKTM+O61mjSRjZBjGz2hqKMn0A2cxD1/+ZmNjtI5CJIO6W4= 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=QwXyhJra; arc=none smtp.client-ip=192.198.163.15 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="QwXyhJra" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=intel.com; i=@intel.com; q=dns/txt; s=Intel; t=1718510475; x=1750046475; h=message-id:date:mime-version:subject:to:cc:references: from:in-reply-to:content-transfer-encoding; bh=LOBeSDMLvjOcAiROl79GUg1b1Ol44rfsv4ROT9gOiwM=; b=QwXyhJra17edh9OMySGRiZ7BTqZK8Nere+NQsUKOT8LxDgUd4fzB2oPC mqrvl7uIMrGI/roBHTSKkoedHdpUhYAL1qS2nj6HYTacutn3vYdnMr2vC DI68X5fq1Uqy6sKBaDPGjReq/BMS1FSRNMrYAONWsGro1XXiXdwv+XLUV DPi90QaFNe1GHINqtEd6nIw0hEmzYYPzEdBUBD7KKQPOcd03baYAXuT7A KsPBrEhuvG5zASk3TNjzhYmYdbtIzWmbP9vAk0ycDOJdkkKOEwoFNSV4n 0fVfHYbWfvHLFN6YQl/9XJvGW9DRS2GBDc8PA9fmlBczqgqE49T/YyR60 w==; X-CSE-ConnectionGUID: w+lQzJn7RJCGz6sy68s8BQ== X-CSE-MsgGUID: lWc7TzTATCmV5nyWzRuy7A== X-IronPort-AV: E=McAfee;i="6700,10204,11104"; a="15521681" X-IronPort-AV: E=Sophos;i="6.08,241,1712646000"; d="scan'208";a="15521681" Received: from orviesa008.jf.intel.com ([10.64.159.148]) by fmvoesa109.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 15 Jun 2024 21:01:14 -0700 X-CSE-ConnectionGUID: jg446RxPQhqExQiBLcU+1g== X-CSE-MsgGUID: SUtQbsIdSLG7yt5XT8M2Qg== X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="6.08,241,1712646000"; d="scan'208";a="41557169" Received: from yma27-mobl.ccr.corp.intel.com (HELO [10.124.232.251]) ([10.124.232.251]) by orviesa008-auth.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 15 Jun 2024 21:01:13 -0700 Message-ID: <3fa7c6c4-d9e4-4233-93a7-12e5d34ee4d0@intel.com> Date: Sun, 16 Jun 2024 12:01:09 +0800 Precedence: bulk X-Mailing-List: linux-fsdevel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 1/3] fs/file.c: add fast path in alloc_fd() To: Mateusz Guzik Cc: viro@zeniv.linux.org.uk, brauner@kernel.org, jack@suse.cz, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, tim.c.chen@linux.intel.com, tim.c.chen@intel.com, pan.deng@intel.com, tianyou.li@intel.com, yu.ma@intel.com References: <20240614163416.728752-1-yu.ma@intel.com> <20240614163416.728752-2-yu.ma@intel.com> Content-Language: en-US From: "Ma, Yu" In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 6/15/2024 2:31 PM, Mateusz Guzik wrote: > On Fri, Jun 14, 2024 at 12:34:14PM -0400, Yu Ma wrote: >> There is available fd in the lower 64 bits of open_fds bitmap for most cases >> when we look for an available fd slot. Skip 2-levels searching via >> find_next_zero_bit() for this common fast path. >> >> Look directly for an open bit in the lower 64 bits of open_fds bitmap when a >> free slot is available there, as: >> (1) The fd allocation algorithm would always allocate fd from small to large. >> Lower bits in open_fds bitmap would be used much more frequently than higher >> bits. >> (2) After fdt is expanded (the bitmap size doubled for each time of expansion), >> it would never be shrunk. The search size increases but there are few open fds >> available here. >> (3) There is fast path inside of find_next_zero_bit() when size<=64 to speed up >> searching. >> >> With the fast path added in alloc_fd() through one-time bitmap searching, >> pts/blogbench-1.1.0 read is improved by 20% and write by 10% on Intel ICX 160 >> cores configuration with v6.8-rc6. >> >> Reviewed-by: Tim Chen >> Signed-off-by: Yu Ma >> --- >> fs/file.c | 9 +++++++-- >> 1 file changed, 7 insertions(+), 2 deletions(-) >> >> diff --git a/fs/file.c b/fs/file.c >> index 3b683b9101d8..e8d2f9ef7fd1 100644 >> --- a/fs/file.c >> +++ b/fs/file.c >> @@ -510,8 +510,13 @@ static int alloc_fd(unsigned start, unsigned end, unsigned flags) >> if (fd < files->next_fd) >> fd = files->next_fd; >> >> - if (fd < fdt->max_fds) >> + if (fd < fdt->max_fds) { >> + if (~fdt->open_fds[0]) { >> + fd = find_next_zero_bit(fdt->open_fds, BITS_PER_LONG, fd); >> + goto success; >> + } >> fd = find_next_fd(fdt, fd); >> + } >> >> /* >> * N.B. For clone tasks sharing a files structure, this test >> @@ -531,7 +536,7 @@ static int alloc_fd(unsigned start, unsigned end, unsigned flags) >> */ >> if (error) >> goto repeat; >> - >> +success: >> if (start <= files->next_fd) >> files->next_fd = fd + 1; >> > As indicated in my other e-mail it may be a process can reach a certain > fd number and then lower its rlimit(NOFILE). In that case the max_fds > field can happen to be higher and the above patch will fail to check for > the (fd < end) case. Thanks for the good catch, replied in that mail thread for details. > >> -- >> 2.43.0 >>