From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752681Ab2IPM0P (ORCPT ); Sun, 16 Sep 2012 08:26:15 -0400 Received: from mail-pz0-f46.google.com ([209.85.210.46]:51195 "EHLO mail-pz0-f46.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752472Ab2IPM0N (ORCPT ); Sun, 16 Sep 2012 08:26:13 -0400 From: Namjae Jeon To: fengguang.wu@intel.com Cc: linux-kernel@vger.kernel.org, Namjae Jeon , Namjae Jeon , Vivek Trivedi Subject: [PATCH v3 2/2] Documentation: add description of dirty_background_centisecs Date: Sun, 16 Sep 2012 08:26:04 -0400 Message-Id: <1347798364-2864-1-git-send-email-linkinjeon@gmail.com> X-Mailer: git-send-email 1.7.9.5 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Namjae Jeon This commit adds dirty_background_centisecs description in bdi sysfs documentation. Signed-off-by: Namjae Jeon Signed-off-by: Vivek Trivedi --- Documentation/ABI/testing/sysfs-class-bdi | 25 +++++++++++++++++++++++++ 1 file changed, 25 insertions(+) diff --git a/Documentation/ABI/testing/sysfs-class-bdi b/Documentation/ABI/testing/sysfs-class-bdi index 5f50097..6869736 100644 --- a/Documentation/ABI/testing/sysfs-class-bdi +++ b/Documentation/ABI/testing/sysfs-class-bdi @@ -48,3 +48,28 @@ max_ratio (read-write) most of the write-back cache. For example in case of an NFS mount that is prone to get stuck, or a FUSE mount which cannot be trusted to play fair. + +dirty_background_centisecs (read-write) + + It is used to start early writeback of given bdi once bdi dirty + data exceeds product of average write bandwidth and + dirty_background_centisecs. It works in parallel of + dirty_writeback_centsecs and dirty_expire_interval based periodic + flushing mechanism. + + It is mainly useful for tuning writeback speed at 'NFS Server' + sothat NFS client could see better write speed. + A good use case is setting it to around 100 (1 second) in the NFS + server for improving NFS write performance. Note that it's not + recommended to set it to a too small value, which might lead to + unnecessary flushing for small IO size. + Setting it to 0 disables the feature. + + However, sometimes it may not match user expectations as it is based + on bdi write bandwidth estimation. The users should not expect this + threshold to work accurately. + Write bandwidth estimation is a best effort to estimate bdi write + speed bandwidth. But it can be wildly wrong in certain situations + such as sudden change of workload (including the workload startup + stage), or if there are no heavy writes since boot, in which case + there is no reasonable estimation yet. -- 1.7.9.5