Swapping to a large sparse file

[jd1008]

On 01/16/2015 07:11 PM, John Morris wrote:
> On Fri, 2015-01-16 at 14:26 -0700, jd1008 wrote:
>
>> In older "traditional" practices, swap space was normally
>> about twice the ram size. Today, with some systems having
>> 64 and even 128GB and even larger RAM, it becomes interesting
>> how big swap space should be. Where is the cutoff for performance?
>> Paging in and out 128GB memory space could prove to be itself a
>> performance bottleneck on very busy or memory bound servers.
> My advice is don't bother unless you know you need it.  I find 512MB or
> 1GB to be plenty of swap.  You need some swap just so the system can
> ditch memory that was used once to initialize code but isn't accessed
> again and other similar things that can be safely tossed to swap and
> forgot about.  But if the system is actually swapping hundreds of
> megabytes in and out you will quickly be in a world of pain.  Plus most
> of the time when that sort of memory pressure hits it is a runaway
> process that the OOM killer will eventually take out and having a lot of
> swap only increases how long you suffer with an almost totally
> unresponsive machine until that happens.  If you are swapping and it
> isn't a runaway process or an exception to process a one off huge
> dataset it is a sign you need to bite the bullet and get more ram.  If
> you know you are going to need a lot of swap to get through some script
> you banged out that allocates memory like mad, just add an extra
> swapfile on a temporary basis and drop it when you are done.  You are
> allowed to have multiple swap files, partitions or any combination of
> them within sensible limits.
>
>
Well, I need at least 8GB of swap if I want to hibernate, and often
I need to hibernate so I can let an important app continue where
it left off (apps that do not depend on an internet continuous connection)
.