38:T432,

Page faults occurs when the process tries to access a memory that isn’t backed by a physical page kernel raises a fault which loads a page. It happens on first access, stack expansion, COW, swap and much more. However it comes with a cost.

In this episode of the backend engineering show I dissect the need and the cost page faults in the kernel.

0:00 Intro
4:00 Virtual memory

Abstraction of physical memory
Memory sharing
Allow more processes to run , unused go to disk
Numa, kernel can place memory near the cpu

12:00 VMA areas

Text/code
Data
BSS
Heap
Stack

19:50 Kernel mode
25:30 What is a Page fault?
30:30 First access page fault
33:00 Stack Expansion page fault
34:30 CoW page fault
38:00 Swap page fault
39:39 File backed page fault
40:29 Permission page fault
45:30 Summary

39:T47f,Fundamentals of Operating Systems Course https://oscourse.winktls is brilliant.TLS encryption/decryption often happens in userland. While TCP lives in the kernel. With ktls, userland can hand the keys to the kernel and the kernel does crypto. When calling write, the kernel encrypts the packet and send it to the NIC.When calling read, the kernel decrypts the packet and handed it to the userspace. This mode still taxes the host’s CPU of course, so there is another mode where the kernel offloads the crypto to the NIC device! Host CPU becomes free. Incoming packets to the NIC are decrypted in device before they are DMAed to the kernel. outgoing packets are encrypted before they leave the NIC to the network.ktls still need handshake to happen in userspace. There is also enabling zerocopy in some cases (now that kernel has context) Deserves a video. So much good stuff.0:00 Intro2:00 Userspace SSL Libraries 3:00 ktls 6:00 Kernel Encrypts/Decrypts (TLS_SW)8:20 NIC offload mode (TLS_HW)10:15 NIC does it all (TLS_HW_RECORD)12:00 Write TX Example13:50 Read RX Example17:00 Zero copy (sendfile)https://docs.kernel.org/networking/tls-offload.html

TCP Protective Load Balancing coming to ...