[CentOS] Why swap if there's still physical memory available

Les Mikesell lesmikesell at gmail.com
Mon Nov 16 23:02:01 UTC 2009

nate wrote:
> yanagik317 wrote:
>> I guess the answer may not be that simple and I most likely haven't
>> described everything that could have influenced the kernel's
>> decision-making, but how does Linux decide how much of a process to be
>> swapped out?  I guess I could read the documentations on the Linux
>> kernel, but does anyone have more general answers ready to be dispensed?
> Linux by default will try to swap less accessed regions of memory
> when memory pressure starts to get tight(say less than 25% of memory
> is free), if you want to override this behavior look to the
> 'swappiness' setting
>> I haven't done anything with sysctl, if that comes into play at all.
> It can if you want
> vm.swappiness = 0
> To tell the kernel not to swap unless it *really* needs to

Also, the top values may not tell the whole story - RES should include 
paged-in code plus memory allocated by the program.   VIRT includes code 
not paged in yet and linked shared libraries, so the difference may not 
all be in swap.

   Les Mikesell
    lesmikesell at gmail.com

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