How Much Memory Is My Program Actually Using
How Much Memory Is My Program Really Using? It seems like such a simple query - but digital memory makes measuring real memory use difficult. Shared memory is just not apportioned per course of using it so it's overstated. Resident memory consists of shared memory, so it overstates as effectively. Digital memory consists of resident memory plus information held in swap, which is not in main memory. Happily unless you are operating a Linux kernel older than the last financial disaster, you may have a greater option: Proportional Set Size (PSS)¹. That is the quantity of non-public memory the method is utilizing, plus its proportional allocation of shared memory. The file lists each memory block mapped to the process, and its properties. You may wrangle the smaps data with shell code, however you don’t should! The smem instrument does that, and it can filter/format too. Memory ideas can be a bit abstract, so let’s take a look at an example.
Now what do you assume the output will show? The little one course of receives a copy of its parent’s memory - so has real memory use doubled? No! The mum or dad and child share the memory; if the child tries to put in writing to any memory it inherited, the kernel will copy the memory web page for the baby to write to (this is known as copy-on-write). The whole resident memory is 167,280 KB however we know that’s a lie - there’s one big array in memory and both processes are sharing it. The full PSS of 82,839 KB is more accurate. If my program exits, how much memory can be reclaimed? While Proportional Set Measurement is beneficial for gauging how a lot memory a process is utilizing, it overstates how a lot memory can be freed when the method exits as shared memory can't be reclaimed. To measure free-ready memory, use Unique Set Size (USS); the sum of all memory pages non-public to the method.
Conveniently, smem already studies USS so there’s no need to write down your personal solution except you’re curious³. This Bash one liner prints its personal memory statistics by operating smem and filtering the output to itself. The USS is 260 KB so I expect to free that a lot real memory when it exits. At 341 KB, PSS is eighty one KB increased, and comprised of its proportional share of /bin/bash (already in memory as I’m launching this from a Bash shell), libc and different shared libraries, and the system locales. The Bash program begins faster as by sharing the libraries already in memory, the kernel doesn’t have to copy them to the program’s memory. Additionally, shared memory reduces total memory use. Digital memory complexifies operating methods but it surely has too much of advantages. 1. PSS was created by Matt Mackall - this LWN article has extra data on its origins. Android taking too long to pattern massive processes’ memory to be able to balance Memory Wave Workshop swimming pools. 3. And if you are curious, this neat golang script by Viacheslav Biriukov calculates the Unique Set Dimension for a given PID. The pagemap interface and USS algorithm is described here.
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