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How sendfile and splice Work: Pipe Buffers, Page References, and Why Zero-Copy Is Not Zero Work

A static file server that uses read() into a user buffer and write() onto a socket copies every byte twice through the CPU: page cache to ...

Sarthak Bystander 30 Sept, 2026

Latest Posts

How sendfile and splice Work: Pipe Buffers, Page References, and Why Zero-Copy Is Not Zero Work

A static file server that uses read() into a user buffer and write() onto a socket copies every byte twice through the CPU: page cache to ...

Sarthak Bystander 30 Sept, 2026

How Linux Interrupts Work: Hardware IRQs, Softirqs, and Why Threaded Handlers Exist

A NIC that just received a frame cannot wait for the current process to finish a syscall. The device raises a hardware interrupt. The CPU st...

Sarthak Bystander 29 Sept, 2026

How Linux Signals Work: Pending Masks, Delivery on Return to Userspace, and Why They Are Not Interrupts

A process that spends all its time in a tight userspace loop never notices SIGTERM until the kernel has a chance to put that process back on...

Sarthak Bystander 28 Sept, 2026

How the Linux Page Cache Works: Radix Trees, Writeback, and Why read() Hits DRAM

A process asks for a few bytes from a file. The kernel may return them without asking the storage device for anything at all—not because the...

Sarthak Bystander 27 Sept, 2026

How Futexes Work: Userspace Fast Path, Wait Queues, and Why Mutexes Avoid Syscalls

A mutex that takes a system call on every lock and unlock would dominate a hot critical section. The uncontended case is a few atomic instru...

Sarthak Bystander 25 Sept, 2026

How epoll Works: Readiness, Level vs Edge Trigger, and Why select Doesn't Scale

A process that accepts ten thousand TCP connections cannot afford to ask the kernel about each socket in turn. select(2) and poll(2) copy ...

Sarthak Bystander 24 Sept, 2026

How RCU Works: Grace Periods, Quiescent States, and Why Readers Skip Locks

A shared linked list in the kernel can be walked by thousands of cores at once. A writer still has to insert or delete a node. If every walk...

Sarthak Bystander 23 Sept, 2026

How Linux CFS Works: vruntime, Red-Black Trees, and Why Fairness Is Approximate

A CPU core runs one thread at a time. Everything else that looks concurrent is a lie the operating system maintains by switching. The policy...

Sarthak Bystander 22 Sept, 2026

How eBPF Works: Verifier, Maps, JIT, and Why the Kernel Runs Your Code

A kernel module can do almost anything. That is why loading one is a privileged act and why a bug in one can take the machine with it. eBPF ...

Sarthak Bystander 21 Sept, 2026

How TLS 1.3 Works: Certificates, 1-RTT Handshakes, and Why 0-RTT Is Replayable

TCP can carry bytes in order. It cannot tell you who is on the other end, and it cannot stop a path observer from reading those bytes. HTTPS...

Sarthak Bystander 20 Sept, 2026