解析/proc/[pid]/smaps的Sizes字段：数据类型、4kB倍数及总和上限问询

Great questions about parsing /proc/[pid]/smaps—let's break each one down clearly:

1. Data type for parsing the Sizes field #

The Sizes field in smaps reports the size of a virtual memory area (VMA) in kilobytes, and values can get extremely large—especially on 64-bit systems. To avoid overflow and ensure compatibility:

• In C/C++, go with uint64_t (from <stdint.h>) or unsigned long long. These 64-bit unsigned types can easily handle the maximum possible values from even the largest 64-bit process address spaces. 32-bit types like int or long are risky here, since they top out at 4GB (4194304 kB), which is way smaller than the address space of a modern 64-bit process.
• In scripting languages like Python, just use the built-in int type—Python handles arbitrary-precision integers natively, so you never have to worry about overflow.

2. Are Sizes values always a multiple of 4kB? #

Short answer: Yes, they always are.

Here's why: Every VMA in Linux has page-aligned start and end addresses. That means the size of the area (end_addr - start_addr) is always a multiple of the system's page size. And on virtually all Linux systems, the page size is a multiple of 4kB—whether it's the standard 4kB page, large pages like 2MB/1GB, or even 64kB pages used on some ARM architectures. When converted to kilobytes, all these page sizes translate to multiples of 4, so the Sizes value will always be a multiple of 4kB.

3. Maximum possible sum of all Sizes values #

This depends entirely on the system's virtual address space limits:

• 32-bit Linux: Traditionally, user-space processes can access up to 3GB (with 1GB reserved for the kernel). That makes the maximum sum 3 * 1024 * 1024 = 3145728 kB. Some configurations restrict user space to 2GB, bringing this down to 2097152 kB.
• 64-bit Linux (x86_64): Most systems use a 47-bit virtual address space for userspace, which translates to 128 TB of addressable memory. In kilobytes, that's 128 * 1024 * 1024 * 1024 = 137438953472 kB. Other 64-bit architectures might have different limits, but this is the most common scenario.

内容的提问来源于stack exchange，提问作者Nic Tzan