Re: tmem frontswap without swap file

[Bob Liu <bob.liu@oracle.com>]

On 02/21/2014 12:35 PM, Vasiliy Tolstov wrote:
> 2014-02-20 9:52 GMT+04:00 Vasiliy Tolstov <v.tolstov@selfip.ru>:
>> Hello. I have some problems with swap files in domU - i have ssd disks
>> that caches all io and if user use swap, ssd may fail very often.
>> Is that possible to use tmem frontswap without swap file at all? And
>> transparently push swap pages to tmem?
> 
> 
> Okay as i see it can;'t be possible.
> Another question - is that possible to reserve tmem to domains at specific size?
> For example i need to get 20Gb for one domain and 10Gb for another.
> But if second domain very hungry it can't
> eaten all memory
> 

Two types of page can be stored in tmem: persistent_page and ephemeral_page.

Persistent pages are swapped-out pages, whose date can't be dropped by
tmem. The rule for persistent pages is:
'current_domain_pages +  persistent_pages have to smaller than
domain->max_pages'.

Ephemeral pages are clean pagecache pages, those pages have a copy in
disk already.
The amount number of ephemeral pages are not limited, but XEN host will
reclaim those pages if under memory pressure.
There is a tmem parameter 'weight' which can be used to control how many
ephemeral_pages should be reclaimed between domains.

-- 
Regards,
-Bob