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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 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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