我在一个禁用交换并且禁用内存过量使用的系统上工作。
假设我的进程当前消耗 100 MB 内存，系统可用内存小于 100 MB。
如果我执行 fork() 会失败，因为内核也尝试为子进程分配 100 MB 吗？
我读过Linux在分叉时使用写时复制，因此子和父共享所有页面。所以我猜 fork 应该成功？
假设 fork 成功，假设我在调用 exec() 之前在子进程中有几行代码。因此，父子进程将继续共享文本段，除非子进程触及任何堆内存，否则内存使用量不应有任何变化。这个对吗 ？
Edit: One follow-up question: With swapping/overcommit disabled, can the cumulative VSS
(Virtual Set Size) of all the processes be more than the available physical memory ?
I tried this out. VSS of all the processes can be much more than that of the physical
memory available.
pmap -x output from a process.
total kB 132588 10744 7192
First number - Virtual Set Size
Second number - Resident Set Size
third number - dirty pages
RSS is < 10% of VSS. This is with swapping and overcommit disabled.
For every shared library loaded I see something like the following..
00007fae83f07000 32 24 0 r-x-- librt-2.12.so
00007fae83f0f000 2044 0 0 ----- librt-2.12.so
00007fae8410e000 8 8 8 rw--- librt-2.12.so
00007fae84312000 252 120 0 r-x-- libevent-2.0.so.5.0.1
00007fae84351000 2048 0 0 ----- libevent-2.0.so.5.0.1
00007fae84551000 8 8 8 rw--- libevent-2.0.so.5.0.1
I guess r-x segment is code and rw- is data. But there is a 2 MB segment
that is not loaded. I see this 2 MB segment for every single shared library.
My process loads a lot of shared libraries. That explains the huge difference
between VSS & RSS.
Any idea what is that 2 MB segment per shared library ?
When overcommit is disabled, if this process calls fork() will it fail when
the free memory is less than VSS (132588 Kb) or RSS (10744) ?