We had a serious (lack of) performance issue today with a Linux NFSclient machine, so I spent some time delving into the underdocumentedworld of kernel parameters that affect the Linux NFS client (not the NFSserver, which has better documented stuff).

(I am going to use sysctl(8) notation for kernel tunables.)

The major tunable is sunrpc.udp_slot_table_entries and/or tcp_slot_table_entries . These are the maximum number of outstandingNFS RPC requests

In a previous entry I mentioned that Sun'saddition of mmap() basically forced their hand on having a unifiedbuffer cache. Today I feel like elaborating on that.

The problem with having mmap() and not a unified buffer cache is pagecoherence. If you have some programs using mmap() and some usingregular read() and write() , you will wind up with two copies ofpages, one mapped into process memory and one in the buffer cache.Because virtual memory and the buffer

It's common to say bad things about the GIL (a round of GIL bashing happened recently, for example). I have acontrarian view: I think that the GIL is the right thing for Python.

Python needs some concurrency support, if only so that it can makeinherently blocking operations into non-blocking ones. At the sametime, the thread and shared memory based concurrent programmingmodel is a terrible one that programmers should avoid as much aspossible.

The GIL is good enough and simple enough to