Re: swap on eMMC and other flash

[Adrian Hunter <adrian.hunter@intel.com>]

On 04/04/12 15:47, Arnd Bergmann wrote:
> On Wednesday 04 April 2012, Adrian Hunter wrote:
>> On 30/03/12 21:50, Arnd Bergmann wrote:
>>> (sorry for the duplicated email, this corrects the address of the android
>>> kernel team, please reply here)
>>>
>>> On Friday 30 March 2012, Arnd Bergmann wrote:
>>>
>>>  We've had a discussion in the Linaro storage team (Saugata, Venkat and me,
>>>  with Luca joining in on the discussion) about swapping to flash based media
>>>  such as eMMC. This is a summary of what we found and what we think should
>>>  be done. If people agree that this is a good idea, we can start working
>>>  on it.
>>
>> There is mtdswap.
> 
> Ah, very interesting. I wasn't aware of that. Obviously we can't directly
> use it on block devices that have their own garbage collection and wear
> leveling built into them, but it's interesting to see how this was solved
> before.
> 
> While we could build something similar that remaps blocks between an
> eMMC device and the logical swap space that is used by the mm code,
> my feeling is that it would be easier to modify the swap code itself
> to do the right thing.
> 
>> Also the old Nokia N900 had swap to eMMC.
>>
>> The last I heard was that swap was considered to be simply too slow on hand
>> held devices.
> 
> That's the part that we want to solve here. It has nothing to do with
> handheld devices, but more with specific incompatibilities of the
> block allocation in the swap code vs. what an eMMC device expects
> to see for fast operation. If you write data in the wrong order on
> flash devices, you get long delays that you don't get when you do
> it the right way. The same problem exists for file systems, and is
> being addressed there as well.
> 
>> As systems adopt more RAM, isn't there a decreasing demand for swap?
> 
> No. You would never be able to make hibernate work, no matter how much
> RAM you add ;-)

Have you considered making hibernate work without swap?