question about memory-hotplug

question about memory-hotplug

[tgh]

hi
  I try to understand the memory_hotplug.c   ,but I am confused about 
the mechanism in it
 Does the mem_map is allocated when setup for all the memory page both 
the existing and the hotplug , or  does the mem_map is allocated 
dynamically when a chip of memory is hotpluged ?
 if mem_map is allocated dynamically,does the mem_map is maintained in 
the list or how to deal with it ?
 and if mem_map is allocated dynamically,does system need new node and 
new zone structure to manage the dynamically-allocated memmap ,or not ?
 if  system need new node and new zone structure to manage the 
dynamically-allocated memmap,does system have to be a NUMA-surpport one 
or not?

I  am confused about it

could you help me
Thanks in advance



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Re: question about memory-hotplug

[Yasunori Goto]

Hello.

> hi
>   I try to understand the memory_hotplug.c   ,but I am confused about 
> the mechanism in it
>  Does the mem_map is allocated when setup for all the memory page both 
> the existing and the hotplug , or  does the mem_map is allocated 
> dynamically when a chip of memory is hotpluged ?
>  if mem_map is allocated dynamically,does the mem_map is maintained in 
> the list or how to deal with it ?
>  and if mem_map is allocated dynamically,does system need new node and 
> new zone structure to manage the dynamically-allocated memmap ,or not ?

Basically, memory hotplug code depends on sparsemem. So, I'll
recommend that you should see mm/sparse.c too.
In sparsemem code, mem_map is allocated dynamically, and 
its pointed by mem_section[] array.

(However, x86-64 code has original code. IIRC, its memmap was allcated 
 statically....)

>  if  system need new node and new zone structure to manage the 
> dynamically-allocated memmap,does system have to be a NUMA-surpport one 
> or not?

Pgdat and zone can be allocated dynamically for NUMA system,
but memmap is not pointed by them if sparsemem is on.

Thanks for your concern. :-)

---
Yasunori Goto 



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Re: question about memory-hotplug

[tgh]

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Thank you for your reply

Yasunori Goto 写道:
> Hello.
>
>   
>> hi
>>   I try to understand the memory_hotplug.c   ,but I am confused about 
>> the mechanism in it
>>  Does the mem_map is allocated when setup for all the memory page both 
>> the existing and the hotplug , or  does the mem_map is allocated 
>> dynamically when a chip of memory is hotpluged ?
>>  if mem_map is allocated dynamically,does the mem_map is maintained in 
>> the list or how to deal with it ?
>>  and if mem_map is allocated dynamically,does system need new node and 
>> new zone structure to manage the dynamically-allocated memmap ,or not ?
>>     
>
> Basically, memory hotplug code depends on sparsemem. So, I'll
> recommend that you should see mm/sparse.c too.
> In sparsemem code, mem_map is allocated dynamically, and 
> its pointed by mem_section[] array.
>   
In the traditional linux without sparsemem, there are node-zone-memmap 
mechanism for managing the physical memory,is it right?
while in the sparsemem mechanism, what is the architure of 
node-zone-memmap or node-zone-mem_section[]-mem_map like?

and if the sparsemem is on , buddy still does its work in a mem_map as 
before or does it work in a new way?
and how does virt-to-phy macro (or something like it) work,when there 
are a list of mem_map in the sparsemem system?

> (However, x86-64 code has original code. IIRC, its memmap was allcated 
>  statically....)
>   
does x86-64 not surpport the memory-hotplug,or how does it achieve the 
memory-hotplug ?
>   
>>  if  system need new node and new zone structure to manage the 
>> dynamically-allocated memmap,does system have to be a NUMA-surpport one 
>> or not?
>>     
>
> Pgdat and zone can be allocated dynamically for NUMA system,
> but memmap is not pointed by them if sparsemem is on.
>   
which structure points it ,mem_section[] does it? then what is the 
architure of the node-zone-mem_section[]-mem_map like?

> Thanks for your concern. :-)
>
> ---
> Yasunori Goto 
>
>
>
>
>   


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Re: question about memory-hotplug

[Yasunori Goto]

> In the traditional linux without sparsemem, there are node-zone-memmap 
> mechanism for managing the physical memory,is it right?

Yes.

> while in the sparsemem mechanism, what is the architure of 
> node-zone-memmap or node-zone-mem_section[]-mem_map like?

mem_section[] is "static array" which is defined in sparse.c.
So, no pointer is necessary to point mem_section array.
Its index can be found by only pfn like ((pfn >> PFN_SECTION_SHIFT)).
Each mem_section has pointer of mem_map.

In addition, each page->flags has area for saving mem_section's index.
page_to_section() is (page->flags >> SECTIONS_PGSHIFT) & SECTIONS_MASK).

Tracing __pfn_to_page() and __page_to_pfn in 
include/asm-generic/memory_model.h will be good answer 
for your understanding.

> and if the sparsemem is on , buddy still does its work in a mem_map as 
> before or does it work in a new way?

2.6.10 or older kernel has bitmaps to manage buddy page. Current
one doesn't have it. Its information is saved in page->private.
Others are same.
1 section size is bigger than MAX_ORDER. So, current buddy system
doensn't concern about section size. 
This means memory hotplug unit size is section size. (At least now)

> and how does virt-to-phy macro (or something like it) work,when there 
> are a list of mem_map in the sparsemem system?
> 
> > (However, x86-64 code has original code. IIRC, its memmap was allcated 
> >  statically....)
> >   
> does x86-64 not surpport the memory-hotplug,or how does it achieve the 
> memory-hotplug ?

x86-64 supports both of sparse and non sparse. It is seleced by
kernel config option.

Bye.

-- 
Yasunori Goto 



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Re: question about memory-hotplug

[tgh]

[-- Warning: decoded text below may be mangled, UTF-8 assumed --]
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Thank you for your reply

If sparsememory is on ,are there node and zone structures or not in the 
systme?

Thanks in advance


Yasunori Goto 写道:
>> In the traditional linux without sparsemem, there are node-zone-memmap 
>> mechanism for managing the physical memory,is it right?
>>     
>
> Yes.
>
>   
>> while in the sparsemem mechanism, what is the architure of 
>> node-zone-memmap or node-zone-mem_section[]-mem_map like?
>>     
>
> mem_section[] is "static array" which is defined in sparse.c.
> So, no pointer is necessary to point mem_section array.
> Its index can be found by only pfn like ((pfn >> PFN_SECTION_SHIFT)).
> Each mem_section has pointer of mem_map.
>
> In addition, each page->flags has area for saving mem_section's index.
> page_to_section() is (page->flags >> SECTIONS_PGSHIFT) & SECTIONS_MASK).
>
> Tracing __pfn_to_page() and __page_to_pfn in 
> include/asm-generic/memory_model.h will be good answer 
> for your understanding.
>
>   
>> and if the sparsemem is on , buddy still does its work in a mem_map as 
>> before or does it work in a new way?
>>     
>
> 2.6.10 or older kernel has bitmaps to manage buddy page. Current
> one doesn't have it. Its information is saved in page->private.
> Others are same.
> 1 section size is bigger than MAX_ORDER. So, current buddy system
> doensn't concern about section size. 
> This means memory hotplug unit size is section size. (At least now)
>
>   
>> and how does virt-to-phy macro (or something like it) work,when there 
>> are a list of mem_map in the sparsemem system?
>>
>>     
>>> (However, x86-64 code has original code. IIRC, its memmap was allcated 
>>>  statically....)
>>>   
>>>       
>> does x86-64 not surpport the memory-hotplug,or how does it achieve the 
>> memory-hotplug ?
>>     
>
> x86-64 supports both of sparse and non sparse. It is seleced by
> kernel config option.
>
> Bye.
>
>   


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Re: question about memory-hotplug

[Yasunori Goto]

> Thank you for your reply

You are welcome.

> If sparsememory is on ,are there node and zone structures or not in the 
> systme?

Yes there are. Zone is still necessary for page reclaim.
Node and zonelist are used for NUMA system.

Thanks.

-- 
Yasunori Goto 



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Re: question about memory-hotplug

[tgh]

Thank you for your reply

> Yes there are. Zone is still necessary for page reclaim.
> Node and zonelist are used for NUMA system.
>   
Buddy allocate memory with the mem_section[] and without  zone-aware 
,while it reclaim memory with zone,is it right?
I am confused about the functions of the zone and node in the system 
,when the sparsemem is on

could you help me
Thanks in advance 




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Re: question about memory-hotplug

[Yasunori Goto]

> > Yes there are. Zone is still necessary for page reclaim.
> > Node and zonelist are used for NUMA system.
> >   
> Buddy allocate memory with the mem_section[] and without  zone-aware 
> ,while it reclaim memory with zone,is it right?
> I am confused about the functions of the zone and node in the system 
> ,when the sparsemem is on

Basically, mem_section[] is for pointer to mem_map.
It doesn't count how many pages are allocated/freed in its section. 
This just divides mem_map[] as discontiguous.

Buddy allocater must know 2 things. 

First is the address of buddy page against target page.
It can be calculated as --relative offset-- from target page.
(See: __page_find_buddy()). So, buddy allocater doesn't know mem_map is 
discontigous or not.
From this view point, Buddy allocater doen't concern about any
zone, node, nor mem_section.

Second is free_list for managing free pages. Its list is connected
to zone. So, buddy allocator must know about only zone's address
and target page's address. It doesn't know mem_map is contiguous
or not too.

Current zone is used for manage freed/active/inactive pages.
Zone has link lists and counters of their pages.
There is no assumption that zone is contiguous from this view point.
Even if there is a memory hole in zone, zone can work.

Just memmap array has assumption that physicall memory is contigous.
Index of memmap is decided by Page Frame Number. If there is big
memory hole in memory, many space of it will be wasted.
This is why mem_section is used for sparse mem.

Node is for NUMA node now. Each node have each pgdat. This is
unit for managing memory areas which has different access
speed. Kernel can use nearest memory from cpu by finding appropriate
pgdat. 

Old DISCONTIG_MEM defines one pgdat for one contigous memory area.
But many people dislike now. If system has too much memory area 
which area is small size, too much pgdats and big zonelists
are big cause of system load.


Bye.

-- 
Yasunori Goto 



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Re: question about memory-hotplug

[tgh]

[-- Warning: decoded text below may be mangled, UTF-8 assumed --]
[-- Attachment #1: Type: text/plain; charset="windows-1252", Size: 2764 bytes --]

Thank you for your reply

Thank you


Yasunori Goto 写道:
>>> Yes there are. Zone is still necessary for page reclaim.
>>> Node and zonelist are used for NUMA system.
>>>   
>>>       
>> Buddy allocate memory with the mem_section[] and without  zone-aware 
>> ,while it reclaim memory with zone,is it right?
>> I am confused about the functions of the zone and node in the system 
>> ,when the sparsemem is on
>>     
>
> Basically, mem_section[] is for pointer to mem_map.
> It doesn't count how many pages are allocated/freed in its section. 
> This just divides mem_map[] as discontiguous.
>
> Buddy allocater must know 2 things. 
>
> First is the address of buddy page against target page.
> It can be calculated as --relative offset-- from target page.
> (See: __page_find_buddy()). So, buddy allocater doesn't know mem_map is 
> discontigous or not.
> From this view point, Buddy allocater doen't concern about any
> zone, node, nor mem_section.
>
> Second is free_list for managing free pages. Its list is connected
> to zone. So, buddy allocator must know about only zone's address
> and target page's address. It doesn't know mem_map is contiguous
> or not too.
>
> Current zone is used for manage freed/active/inactive pages.
> Zone has link lists and counters of their pages.
> There is no assumption that zone is contiguous from this view point.
> Even if there is a memory hole in zone, zone can work.
>
> Just memmap array has assumption that physicall memory is contigous.
> Index of memmap is decided by Page Frame Number. If there is big
> memory hole in memory, many space of it will be wasted.
> This is why mem_section is used for sparse mem.
>
> Node is for NUMA node now. Each node have each pgdat. This is
> unit for managing memory areas which has different access
> speed. Kernel can use nearest memory from cpu by finding appropriate
> pgdat. 
>
> Old DISCONTIG_MEM defines one pgdat for one contigous memory area.
> But many people dislike now. If system has too much memory area 
> which area is small size, too much pgdats and big zonelists
> are big cause of system load.
>
>
> Bye.
>
>   


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