Real Kernel RSS Memory Tracking

Standard PHP functions like memory_get_usage() and memory_get_peak_usage() only measure memory allocated inside the Zend Engine heap (the internal memory manager for PHP objects, arrays, and variables).

They are completely blind to memory allocated by:

• C-extensions (curl, imagick, gd, openssl, ext-sodium)
• Native glibc malloc() / jemalloc / mimalloc allocations
• Embedded C/Go worker memory inside FrankenPHP

---

The Linux /proc/self/statm Interface

On Linux, the kernel maintains an ultra-fast pseudo-filesystem file for every process: /proc/self/statm.

Reading this file does not trigger disk I/O; the kernel directly exposes the process memory page table:

20480 12800 3840 256 0 10240 0

Where the values represent:

1. Total Program Size (Size): Total virtual memory size (in pages).
2. Resident Set Size (RSS): Real physical RAM currently occupied by the process (in pages).
3. Shared Pages (Shared): Pages mapped to shared libraries.
4. Text / Code (Text): Executable code segment.
5. Library (Lib): Shared library pages.
6. Data + Stack (Data): Process data segment and user stack.
7. Dirty Pages (Dirty): Modified physical memory pages.

---

How Leakless Reads and Computes RSS

1. Kernel Page Resolution: Leakless dynamically resolves the Linux kernel page size using POSIX posix_sysconf(POSIX_PC_SC_PAGESIZE) (typically 4096 bytes on x86_64, or 65536 bytes on certain ARM architectures).
2. Low-Overhead Parsing: During startRequest() and endRequest(), Leakless reads /proc/self/statm with zero-allocation string parsing (ProcStatmParser).
3. Conversion: Converts page counts directly to megabytes: $$\text{RSS (MB)} = \frac{\text{resident_pages} \times \text{page_size_bytes}}{1024 \times 1024}$$
4. Memory Drift Calculation: Computes the exact physical memory delta ($\Delta \text{RSS}$) consumed during the active request cycle: $$\Delta \text{RSS} = \text{RSS}{\text{after}} - \text{RSS}{\text{before}}$$

If the Linux /proc filesystem is unavailable (such as during local development on macOS/Windows without Docker), Leakless automatically falls back to memory_get_usage(true) to ensure 100% portability.