[linux-mm-cc] Question using compacache(zram) with multi devices

[Nitin Gupta]

On 12/24/2010 02:05 AM, John McCabe-Dansted wrote:
> On Fri, Dec 24, 2010 at 2:48 PM, Mike Cao<bcao at redhat.com>  wrote:
>> On Thu, 2010-12-23 at 19:07 +0800, John McCabe-Dansted wrote:
>>> On Thu, Dec 23, 2010 at 6:24 PM, Mike Cao<bcao at redhat.com>  wrote:
>>>> I wonder whether the /dev/zramX means zcache pools?
>>>
>>>  From the page you linked "zram can be used to provide a compressed
>>> swap, while zcache compresses filesystem cache pages". AFAICT zram and
>>> zcache are two different tools for two different purposes.
>>>
>> I thought they should be the same thing, zcache now called zram.if
>> not ,how we can make zcache tool ?
>
> I haven't found instructions on how to use zcache, but the difference
> between zram and zcache is discussed here:
>
> http://lwn.net/Articles/397574/
>

The article is slightly misleading -- it gives the impression that 
zcache was developed to *replace* zram.   In fact, zram and zcache are 
quite different: zcache compresses filesystem caches only and not 
anonymous (heap) pages, OTOH zram compression only anonymous pages and 
not pagecache pages.

Currently, there is no easy way to test zcache as cleancache -- which is 
zcache's backend -- is not yet in mainline (or even staging).


Nitin