"Marc G. Fournier" wrote:
> > No, there's no stats collected on this stuff, because it's a
> > pretty obvious and straight-forward thing: you have to have a
> > KVA space large enough that, once you subtract out 4K for each
> > 4M of physical memory and swap (max 4G total for both), you
> > end up with memory left over for the kernel to use, and your
> > limits are such that the you don't run out of PTEs before you
> > run out of mbufs (or whatever you plan on allocating).
> ... and translated to english, this means? :)
> Okay, I'm going to assume that I'm allowed 4Gig of RAM + 4Gig of Swap, for
> a total of 8Gig ... so, if I subtract out 4K for each 4M, that is 8M for
> ... what?
> So, I've theoretically got 8184M of VM available for the kernel to use
> right now?  what are PTEs and how do I know how many I have right now?  as
> for mbufs, I've currently got:


Each 4M of physical memory takes 4K of statically allocated KVA.
Each 4M of backing store takes 4K of statically allocated KVA.

The definition of "backing store" includes:

o       All dirty data pages in swap
o       All dirty code pages in swap
o       All clean data pages in files mapped into process or kernel
        address space
o       All clean code pages for executables mapped into process or
        kernel address space
o       Reserved mappings for copy-on-write pages that haven't yet
        been written

A PTE is a "page table entry".  It's the 32 bit value in the page
table for each address space (one for the kernel, one per process).
See the books I posted the titles of for more details, or read the
Intel processor PDF's from their developer web site.

> jupiter> netstat -m
> 173/1664/61440 mbufs in use (current/peak/max):
>         77 mbufs allocated to data
>         96 mbufs allocated to packet headers
> 71/932/15360 mbuf clusters in use (current/peak/max)
> 2280 Kbytes allocated to network (4% of mb_map in use)
> 0 requests for memory denied
> 0 requests for memory delayed
> 0 calls to protocol drain routines
>         So how do I find out where my PTEs are sitting at?

The mbufs are only important because most people allocate a
large number of mbufs up front for networking applications, or
for alrge numbers of users with network applications that will
need resources in order to be able to actually run.  There's
also protocol control blocks and other allocation that occur
up front, based on the maximum number of system open files
and sockets you intend to permit.

The user space stuff is generally a lot easier to calculate:
do a "ps -gaxl", round each entry in the "VSZ" column up to
4M, divide by 4K, and that tells you how many 4K units you
have allocated for user space.  For kernel space, the answer
is that there are some allocated at boot time, (120M worth),
and then the kernel map is grown, as necessary, until it hits
the KVA space limit.  If you plan on using up every byte, then
divide your total KVA space by 4K to get the number of 4K pages
allocated there.

For the kernel stuff... you basically need to know where the
kernel puts how much memory, based on the tuning parameters
you use on it.

-- Terry

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