On Tue, 17 Jul 2018 02:15:17 -0000, David Frank said: > inking. I'm checking out if the flag does what is is said to do-- I don't > have > to call msync function, which would boost performance.
Note that this can actually *kill* performance, because this means that the kernel has to flush to backing store every single time it notes a change, whereas if you use msync only at those points your software needs a sync point, it can do it at only those points.... Thought experiment: Imagine a workflow that needs to checkpoint every 1000 changes to the shared segment (for instance, if you've mapped an array with 1000 rows, do a for() loop across it incrementing one item, and checkpoint when they're all incremented). msync after the loop completes is one sync, while a worst-case using MAP_SYNC could result in a flush after every single increment (if the system is rescheduling the process over and over - for instance, if there's also another syscall inside the loop).
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