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Message-Id: <1347798364-2864-1-git-send-email-linkinjeon@gmail.com>
Date: Sun, 16 Sep 2012 08:26:04 -0400
From: Namjae Jeon <linkinjeon@...il.com>
To: fengguang.wu@...el.com
Cc: linux-kernel@...r.kernel.org, Namjae Jeon <linkinjeon@...il.com>,
Namjae Jeon <namjae.jeon@...sung.com>,
Vivek Trivedi <t.vivek@...sung.com>
Subject: [PATCH v3 2/2] Documentation: add description of dirty_background_centisecs
From: Namjae Jeon <namjae.jeon@...sung.com>
This commit adds dirty_background_centisecs description in bdi sysfs
documentation.
Signed-off-by: Namjae Jeon <namjae.jeon@...sung.com>
Signed-off-by: Vivek Trivedi <t.vivek@...sung.com>
---
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
--
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