Re: [PATCH 0/4] Swap migration V3: Overview

[KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>]

mike kravetz wrote:
>>yea, looks nice :)
>>But such pages are already shown as hotpluggable, I think.
>>ACPI/SRAT will define the range, in ia64.
> 
> 
> I haven't taken a close look at that code, but don't those just give
> you physical ranges that can 'possibly' be removed? 

It just represents pages are physically hotpluggable or not.

> So, isn't it
> possible for hotpluggable ranges to contain pages allocated for kernel
> data structures which would be almost impossible to offline?
> 
The range which contains kernel data isn't hot-pluggable.
So such range shouldn't contain the kernel pages.

As you say, it's very helpful to show how section is used.
But I think showing hotpluggable-or-not looks enough.(KERN mem is not hotpluggable)
Once a section turned to be KERN section, it's never be USER section, I think.

>>The difficulty is how to find hard-to-migrate pages, as Andrew pointed out.
> 
> 
> By examining the fragmentation usemaps, we have a pretty good idea about
> how the blocks are being used.  If a block is flagged as 'User Pages' then
> there is a good chance that it can be offlined.  
yes.

But 'search and find on demand' approach  is not good for the system admin
who makes system resizing plan.
Do you consider some guarantees to keep quantity or location of not-hottpluggable
memory section ?

-- Kame


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