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 Post subject: Linux: What is nr_pdflush_threads?
PostPosted: Fri Mar 13, 2009 3:50 am 

Joined: Wed Jul 18, 2007 1:14 am
Posts: 181
Question: What is nr_pdflush_threads?

Ans: Linux usually writes data out of the page cache using a process called pdflush. At any moment, between 2 and 8 pdflush threads are running on the system. You can monitor how many are active by looking at /proc/sys/vm/nr_pdflush_threads. Whenever all existing pdflush threads are busy for at least one second, an additional pdflush daemon is spawned. The new ones try to write back data to device queues that are not congested, aiming to have each device that's active get its own thread flushing data to that device. Each time a second has passed without any pdflush activity, one of the threads is removed.

In hundredths of a second, this is how often pdflush wakes up to write data to disk. The default wakes up the two (or more) active threads every five seconds.

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