Alright, that lets me know that it's not an entirely bad thing. It does say, however, that it's fine as long as the free memory isn't REALLY low. It did get down to 13MB though, as I said.
Really low means less than 1 MB. That would indicate the VM system is under so much pressure that it can't maintain the minimum amount of free space it wants to have:
vm.v_free_min: 378 vm.v_free_target: 1655 vm.v_free_reserved: 143 vm.v_pageout_free_min: 34 vm.v_free_severe: 260
These numbers are likely to be in 4K pages, 260 * 4K = 1040K ~= 1 MB, and will vary slighty depending on available physical RAM, kernel size, and probably the phase of the moon. :-)
So now I understand that it's alright for the free memory to be low. I don't understand how the inactive, cache, and buffered memory are
used though. When a process uses up all the free memory, does it then
use some from inactive, or does it use swap?
A process will start reusing inactive memory, which involves flushing data to disk and/or using swap, depending, but the VM system may well swap out pages from other processes instead (especially ones that have been idle for a long time).
[ The VM pager uses LRU or actually NFU page selection algorithms with complex names like "second chance replacement via clock hand sweep, with working set size and global page-fault frequency modelling". :-) This is a complicated topic, and it starts becoming better to look at the code than to try to describe the algorithms in words. ]
-- -Chuck
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