[ltp] Re: ThinkPad 600... Xubuntu... Maxxed Out Memory

[Stefan Monnier]

> Let me get this straight: The machine doesn't have enough RAM, so you take
> some of that precious RAM and make it unavailable to programs, so the OS can
> swap RAM into and out of this reserved RAM, compressing and uncompressing it
> when it's needed?

That's right.

> And it's supposed to be faster?

Yup.  Obviously, only in some cases.  If you use little RAM, it
shouldn't make any difference.  If you use just a bit less than all your
RAM, the compcache will slow you down because you'll be swapping
intou/outof the compcache.  But if you need a bit more than all your RAM
(but not too much more, so it does fit within the compcache), then
you'll go faster because you swap to compressed RAM rather than to disk.

When using a lot of memory a well-designed compcache can also help if it
ends up compressing the swap space (i.e. you first compress into the
compcache and then swap from there to disk) and hence increase the
apparent bandwidth of your swap disk.  IIUC Linux's current compcache
doesn't really do this quite right yet.


        Stefan