Controls the number of kernel threads that perform asynchronous I/O for the NFS version 2 client. Because NFS is based on RPC and RPC is inherently synchronous, separate execution contexts are required to perform NFS operations that are asynchronous from the calling thread.
The operations that can be executed asynchronously are read for read-ahead, readdir for readdir read-ahead, write for putpage and pageio operations, commit, and inactive for cleanup operations that the client performs when it stops using a file.
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Yes, but this parameter is set per file system at mount time. To affect a particular file system, unmount and mount the file system after changing this parameter.
To increase or reduce the number of simultaneous I/O operations that are outstanding at any given time. For example, for a very low bandwidth network, you might want to decrease this value so that the NFS client does not overload the network. Alternately, if the network is very high bandwidth, and the client and server have sufficient resources, you might want to increase this value. Doing so can more effectively utilize the available network bandwidth, and the client and server resources.