X11 on small systems?

[Joshua Judson Rosen]

Benjamin Scott <dragonhawk at gmail.com> writes:
> On Mon, Sep 13, 2010 at 4:47 PM, Joshua Judson Rosen
> <rozzin at geekspace.com> wrote:
> >
> > Yes, however: several of the libraries that are exclusive to
> > the X server are actually things that would (or could) be eliminated
> > in different use-cases; the 4-MB Intel DRI module, for example,
> 
>   Good point.  X.org doesn't necessarily have to be as heavy as it is
> on a desktop PC.   And has been mentioned, there are more lightweight
> X servers out there.

... assuming that you even need an X server :)

> > > Virtual size can include things which aren't main RAM.
> >
> > I'm going to go a step further, contradicting the prevailing wisdom
> > of the Internet, and say that VSZ can even include that aren't even
> > properly `allocated *virtual* memory'. What I mean is:
> >
> >    RSS != (VSZ - (amount of memory paged out to swap))
> 
>   Contrary to popular belief and several OS GUIs, "virtual memory"
> does not mean "using disk as virtual RAM". That is, "virtual memory"
> is *not* synonymous with "swap space".


Note that top(1), of all things, says:

       o: VIRT  --  Virtual Image (kb)
          The  total  amount  of virtual memory used by the task.  It includes
          all code, data and  shared  libraries  plus  pages  that  have  been
          swapped out.

          VIRT = SWAP + RES.

       p: SWAP  --  Swapped size (kb)
          The swapped out portion of a task’s total virtual memory image.

       q: RES  --  Resident size (kb)
          The non-swapped physical memory a task has used.


Is it any wonder that people are confused?

> Virtual memory is the address space seen by a process and provided
> by the MMU.
[... excellent description of paging and what "virtual memory"
     actually means, elided...]
>   My expectation was that "virtual size" was the total size of all
> objects the kernel memory manager had associated with a given
> process's virtual memory space (not necessarily mapped).  That would
> include all "regular" memory allocated, plus every mmap'ed file (and
> thus every shared library).

Exactly--thank you for taking the time to paint the picture more vividly :)


> For X, that might also include video card RAM.  It might even
> include things which have no "real" representation at all:
> 
> blackfire$ sudo memstat | grep nvidia0
>   42560k: PID  3000 (/dev/nvidia0)
> 3278332k: /dev/nvidia0 3000
> blackfire$
> 
>   That's over 3 GiB.   My video card has 256 MiB RAM, main RAM is 1
> GiB.  So whatever that is, it isn't hardware.
[...]
>   But in any event, "virtual memory" doesn't have any necessary
> correlation to committed primary or secondary storage (i.e., RAM or
> disk).

Which reminds me: let's not forget /proc/sys/vm/overcommit* :)

-- 
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