Is it possible to reserve exact amount of space for the indexing and virtual memory? Is it possible to reserve exact amount of space for the indexing and virtual memory?

I have Macbook Air with 128 GB SDD (with OS X Yosemite). When I run out of memory (free space less than 1 GB) the computer slows down and even hangs up.

I suspect that this slow down is due to the impossibility of indexing to be written on the disk and due to a lack of space for the virtual memory.

Is it possible to single out a place to be used only for paging and indexing? For example, to reserve 10 GB for that purpose?

In Linux systems there is a /var folder where these kind of stuff are written. It can be  put on a separate partition and this way to reserve certain amount of space only for itself. Is it possible to do something like this on a Mac in regard to indexing and virtual memory? I would sacrifice 10-15GB for it, if is needed.
As SSDs age, it takes more and more work for them to store data.  This is only made worse by having less than 1GB of space available.  In my experience (with a 2010 Macbook Air, with the 250GB SSD), performance GREATLY improved when I had >10% free space.  

Do what you can to give your computer some breathing room!  Delete some files now!

Here's a classic article on how SSDs work.  Probably TMI, but...
   http://arstechnica.com/information-technology/2012/06/inside-the-ssd-revolution-how-solid-state-disks-really-work/