2 ms·

mmap is not as free as people think. VM subsystem is full of inefficient locks. Here is a very good writeup on a problem BBC encountered with Varnish: https://w

• lrossi 6y ago
  > huge pressure on the virtual memory (VM) subsystem due to extensive dirty page writeback and page steals. The VM subsystem is constantly modifying page table entries (PTEs). This PTE churn results in frequent translation lookaside buffer (TLB) flushes and many inter-processor interrupts (IPIs) to do so. These TLB flushes have a very negative performance hit. Interesting. I was aware of various mmap limitations, but I didn’t think about the TLB changes/flushes, which obviously come with an important overhead.