RE: [Xen-ia64-devel] [PATCH][RFC]discontig memory support

[Kouya SHIMURA <kouya@xxxxxxxxxxxxxx>]

Hi Kevin,

Thanks for your comments.

Tian, Kevin writes:
 > If you can measure the TLB miss ratio of accessing vmemmap, that could 
 > help a lot to make right choice.

My guess is that the TLB miss ratio is quite worse because
vmemmap(frame_table) is usually accessed only by grant table operation
and the locality seems to be less.

I think if the overhead of TLB miss would be enough light, the
performance of VIRTUAL_MEM_MAP is better than SPARCEMEM. But SPARCMEM
is more extensible to implement other functions.

 > So last comment is, you may need to keep 
 > CONFIG_VIRTUAL_MEM_MAP option for a while, instead of merging 
 > code immediately. That can help add or remove a feature as an integrity, 
 > especially when direction is not clear. Also like Linux, it's better to add 
 > a 
 > check upon holes even when CONFIG_VIRTUAL_MEM_MAP is enabled, 
 > since overhead can be avoided on boxes without memory holes by using 
 > physical memmap.

Of course, I leave CONFIG_VIRTUAL_FRAME_MAP.

 > >[TODO]
 > >  * cleanup #ifdefs of CONFIG_VIRTUAL_MEM_MAP
It means that CONFIG_VIRTUAL_MEM_MAP originated in Linux are still
scattered in source code and I will do cleanup.

Thanks,
Kouya


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