* [PATCH v3 2/2] Documentation: add description of dirty_background_centisecs
@ 2012-09-16 12:26 Namjae Jeon
2012-09-20 8:45 ` Fengguang Wu
0 siblings, 1 reply; 2+ messages in thread
From: Namjae Jeon @ 2012-09-16 12:26 UTC (permalink / raw)
To: fengguang.wu; +Cc: linux-kernel, Namjae Jeon, Namjae Jeon, Vivek Trivedi
From: Namjae Jeon <namjae.jeon@samsung.com>
This commit adds dirty_background_centisecs description in bdi sysfs
documentation.
Signed-off-by: Namjae Jeon <namjae.jeon@samsung.com>
Signed-off-by: Vivek Trivedi <t.vivek@samsung.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
^ permalink raw reply related [flat|nested] 2+ messages in thread
* Re: [PATCH v3 2/2] Documentation: add description of dirty_background_centisecs
2012-09-16 12:26 [PATCH v3 2/2] Documentation: add description of dirty_background_centisecs Namjae Jeon
@ 2012-09-20 8:45 ` Fengguang Wu
0 siblings, 0 replies; 2+ messages in thread
From: Fengguang Wu @ 2012-09-20 8:45 UTC (permalink / raw)
To: Namjae Jeon
Cc: Jan Kara, Dave Chinner, linux-kernel, Namjae Jeon, Vivek Trivedi,
Linux Memory Management List, linux-fsdevel
[ add CC ]
On Sun, Sep 16, 2012 at 08:26:04AM -0400, Namjae Jeon wrote:
> From: Namjae Jeon <namjae.jeon@samsung.com>
>
> This commit adds dirty_background_centisecs description in bdi sysfs
> documentation.
>
> Signed-off-by: Namjae Jeon <namjae.jeon@samsung.com>
> Signed-off-by: Vivek Trivedi <t.vivek@samsung.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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