DragonFlyBSD

:New submission from Carlos Olmedo Escobar <carlos.olmedo.e@gmail.com>:
:
:I'm developing a library and I need to take the total/free swap space from a
:sysctl() call (i can use kvm but in this case my lib will need the suid bit).
:This kind of call already exists on FreeBSD (vm.swap_info plus struct xswdev).
:Also in Open/NetBSD.

We currently have (in HEAD):

vm.swap_anon_use    # of pages of anonymous memory swapped out to swap.

vm.swap_cache_use    # of pages of clean data swapped out by swapcache
              (for people with SSDs).

There is no total swap sysctl but I will add one right now.  I will
    call it 'vm.swap_size'.  You will then be able to calculate the
    amount of free swap with (vm.swap_size - vm.anon_use - vm.cache_use).

Currently the list of individual swap devices is not exported.

-Matt
                    Matthew Dillon 
                    <dillon@backplane.com>

Hi! Thanks for your quick answer.

The new sysctl will be useful, but i'll need to retrieve individual swap device
stats too. Are you (or anybody else) going to create this one?

In that case, can we leave this issue open until it's created?

Regards.

:Hi! Thanks for your quick answer.
:
:The new sysctl will be useful, but i'll need to retrieve individual swap device
:stats too. Are you (or anybody else) going to create this one?
:
:In that case, can we leave this issue open until it's created?
:
:Regards.

Hmm.  We don't record individual stats at the moment, which is why
    the libkvm code has to scan the blist (which is slow) to figure
    it out.  It would be fairly easy to add tracking for each device,
    I'll see if I can work something up quickly.

-Matt
                    Matthew Dillon 
                    <dillon@backplane.com>

::The new sysctl will be useful, but i'll need to retrieve individual swap device
::stats too. Are you (or anybody else) going to create this one?
::
::In that case, can we leave this issue open until it's created?
::
::Regards.

Ok, I took a look at FreeBSD's vm.swap_info sysctl and implemented
    something similar.  Ours is slightly different so I named it differently,
    vm.swap_info_array.  Ours takes no arguments and returns the entire
    array.

I adjusted our libkvm code in the DragonFly HEAD so you can get example
    usage from that (/usr/src/lib/libkvm/kvm_getswapinfo.c) if you want
    to call the sysctl directly.

Or you can use the kvm_getswapinfo() call in libkvm and it will use
    the new sysctl if it is available (presuming you recompile libkvm,
    of course, and run a fresh kernel).

-Matt
                    Matthew Dillon 
                    <dillon@backplane.com>