On Dec 4, 2013, at 4:29 PM, Joe Zeff <j...@zeff.us> wrote:

> On 12/04/2013 03:21 PM, Tim wrote:
>> It's probably the reasoning behind make swap twice as big as RAM.  It
>> should leave enough room for RAM to fit into swap, and the wiggle room
>> for the OS to tidy up swap as it hibernates things.
> 
> Sorry, but I have to inform you that you're putting the cart before the 
> horse.  The rule of thumb I mentioned about making swap twice the size of RAM 
> goes back to the early days of MS-DOS, long before there were such things as 
> hibernate or sleep for computers.

Well there's more than one rule of thumb even on linux. And the paging method 
on DOS is different than NT, so it's surely different than linux, BSD, or OS X. 
Case in point, OS X has never had the idea of user configurable swap. The 
dynamic_pager process creates and destroys swapfiles on demand as needed. 

On linux, there have been periodic swap code changes, which can be found by 
doing an lkml search. New in 3.12 is a different block allocation algorithm for 
swap on SSD, for the 3.11 kernel is zswap, and frontswap has been in since 3.5 
kernel.

The anaconda/blivet code suggests upwards of 3x memory if you have less than 
4GB RAM and hibernation applies. Whereas for 8GB or more, the suggestion is 
1.5x memory if hibernation applies. If hibernation doesn't apply suggested swap 
is between 0.5x and 2x RAM.

Chris Murphy
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