Periodic Flushing

Now that you are familiar with the framework in which the pdflush mechanism operates, let's move on to describe the routines responsible for the actual synchronization of cache contents with the associated backing store. Recall that two alternatives are available, one periodic and one enforced. First, let's discuss the periodic writeback mechanism.

In earlier kernel versions, a user mode application was used to perform periodic write operations. This application was started at kernel initialization time and invoked a system call at regular intervals to write back dirty pages. In the meantime, this not particularly elegant procedure was replaced with a more modern alternative that does not take the long route via user mode and is therefore not only more efficient but also more aesthetic.

What's left of the earlier method is the name kupdate. The name appears as a component of some functions and is often used to describe the flushing mechanism.

Two things are needed to periodically flush dirty cache data: the worker function that is executed with the help of the pdflush mechanism, and code to regularly activate the mechanism.

Continue reading here: Mmvmstatc

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