Real Kernel RSS & File Descriptor 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:

• C-extensions (curl, imagick, gd, openssl, ext-sodium)
• Native glibc malloc() / jemalloc / mimalloc allocations
• Unclosed File Descriptors (/proc/self/fd) and lingering sockets

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1. 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 Computes RSS

1. Kernel Page Resolution: Dynamically resolves the Linux page size via POSIX posix_sysconf(POSIX_PC_SC_PAGESIZE) (typically 4096 bytes).
2. Zero-Allocation Parsing: ProcStatmParser reads /proc/self/statm at request boundaries.
3. Megabyte Conversion: Converts page counts directly to megabytes: $$\text{RSS (MB)} = \frac{\text{resident_pages} \times \text{page_size_bytes}}{1024 \times 1024}$$

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2. File Descriptor Guard (/proc/self/fd)

In persistent PHP workers, unclosed file handles (fopen()), temporary streams, or open network sockets (fsockopen(), cURL handles) accumulate in the process table.

Over time, this breaches the operating system limit (ulimit -n), causing fatal errors: Too many open files

How FileDescriptorGuard Operates

When checkFileDescriptors: true (or LEAKLESS_CHECK_FILE_DESCRIPTORS=true):

1. Initial Snapshot: Reads /proc/self/fd symlinks at startRequest().
2. Post-Request Audit: Re-inspects /proc/self/fd at endRequest().
3. Leak Identification: Detects descriptors opened during request processing that were left unclosed.
4. Diagnostic Logging: Emits detailed warnings with file paths and sets $report->fileDescriptorsLeaked = true.