Unsigned long size,resident,share,text,lib,data,dt Ĭonst char* statm_path = "/proc/self/statm" checks the memory usage of the process with one of the methods mentioned at: Memory usage of current process in C.writes one byte on each page to ensure that each of those pages goes from virtual only memory (VSZ) to actually used memory (RSS).allocates more RAM than our physical memory with mmap.Now to observe this in action, let's create a program that: private dirty RSS?įor this to make sense, you have to understand the basics of paging: How does x86 paging work? and in particular that the OS can allocate virtual memory via page tables / its internal memory book keeping (VSZ virtual memory) before it actually has a backing storage on RAM or disk (RSS resident memory). A way to determine a process's "real" memory usage, i.e.There is way more to it than this, to learn more check the following references:
Use ps or top to view this information in linux/unix. Threads all share the same address space, so the RSS, VSZ and PSS for each thread is identical to all of the other threads in the process. So if there were two processes using the same shared library from before: PSS: 400K + (1000K/2) + 100K = 400K + 500K + 100K = 1000K
This is a newer measure which tracks the shared memory as a proportion used by the current process. There is also PSS (proportional set size). So if your program allocated a bunch of memory up front, then uses it over time, you could see RSS going up and VSZ staying the same. The memory that is allocated also may not be in RSS until it is actually used by the program. Since part of the memory is shared, many processes may use it, so if you add up all of the RSS values you can easily end up with more space than your system has. So if process A has a 500K binary and is linked to 2500K of shared libraries, has 200K of stack/heap allocations of which 100K is actually in memory (rest is swapped or unused), and it has only actually loaded 1000K of the shared libraries and 400K of its own binary then: RSS: 400K + 1000K + 100K = 1500K It includes all memory that the process can access, including memory that is swapped out, memory that is allocated, but not used, and memory that is from shared libraries. It does include all stack and heap memory. It does include memory from shared libraries as long as the pages from those libraries are actually in memory. It does not include memory that is swapped out. RSS is the Resident Set Size and is used to show how much memory is allocated to that process and is in RAM.
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