I was trying to see how much I can really allocate memory in kernel
space using "vmalloc". I used "kinfocenter"(the memory section) to
monitor the changes. My laptop has 512MB phyical memory with a 1GB swap
partition.
At the beginning, the system didn't have much free physical memory
available(about %7 free), and rest of the physical memory is ocuppied
by 'application data' and 'disk cache'. At this time, If I tried to
allocate 100MB memory using 'vmalloc' (using a single variable to hold
the memory), I would fail. What I did was gradually increasing
the amount of physical memory to allocate. So, I did: (1) allocate 20MB
and free 20MB, (2) allocate 30MB and free 30MB, (3) allocate 50MB, free
50MB, and so on. As I increased the amount of memory to allocate, the
portion of the 'disk cache' memory just gradually shrinked. And
finally, I could allocate 120MB physical memory. I can't go up to
130MB, doesn't matter how much free physical memory is available in the
system. I can't understand why it's happening.
After the above failure, I tried to use two variable to hold the
allocated memory. I also gradually increased the amount of memory to
allocate. And Finally, each variable could hold 120MB physical memory,
which is 240MB in total. And then, I tried to allocate 130MB to each
variable, I failed. It seemed that 120MB is the maximum memory a single
variable can hold for a system with 512MB physical memory available. I
don't know if my observation can apply to general.
So, I'm interested in knowing if there is a kernel function call to
shrink the kernel caches before I want to allocate huge amount of
memory in a single step, rather than gradually shrink the caches to
make more memory available.
And how can I know how much memory a varialbe can hold in general?
Thanks for your patient to read these a lot of words.
