On 01/17/2015 03:52 PM, Chris Murphy wrote:
On Fri, Jan 16, 2015 at 7:22 PM, jd1008 <jd1008@xxxxxxxxx> wrote:
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)
Does hibernation (suspend to disk) even work with a swapfile? It seems
to depend on the root file system becoming available, so that
/etc/fstab can state what/where the hibernation file is located. But
for a loop mounted swap file, in addition the loop needs to be setup
first. Before that time the swap device doesn't exist. So this seems
difficult.
If you want to hibernate you need 1x RAM at least. The installer
(specifically python-blivet) has laptop hibernation specific code to
create a swap partition that's 2x RAM. This code doesn't get used by
default in Fedora.
So if you need to hibernate I think you're best off with a swap
partition that's 2x RAM. It's suggested it might work with less than
that, but the recommendation is to account for the possibility some
swap is in use at the time the computer hibernates, so it needs enough
space to hold what was use for swap and all of RAM.
Agreed!
The lightweight solution for me is to
get a nand flash stick of 12 or 16GB to remain in the
multi flash reader/writer slot at all times.
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