Re: [00/17] Large Blocksize Support V3

Nick Piggin
2007-04-27T10:08:49Z

Christoph Lameter wrote:
> On Thu, 26 Apr 2007, Nick Piggin wrote:
>
>
>>Christoph Lameter wrote:
>>
>>>On Thu, 26 Apr 2007, Nick Piggin wrote:
>>>
>>>
>>>
>>>>But I maintain that the end result is better than the fragmentation
>>>>based approach. A lot of people don't actually want a bigger page
>>>>cache size, because they want efficient internal fragmentation as
>>>>well, so your radix-tree based approach isn't really comparable.
>>>
>>>
>>>Me? Radix tree based approach? That approach is in the kernel. Do not create
>>>a solution where there is no problem. If we do not want to support large
>>>blocksizes then lets be honest and say so instead of redefining what a block
>>>is. The current approach is fine if one is satisfied with scatter gather and
>>>the VM overhead coming with handling these pages. I fail to see what any of
>>>what you are proposing would add to that.
>>
>>I'm not just making this up. Fragmentation. OK?
>
>
> Yes you are. If you want to avoid fragmentation by restricting the OS to
> 4k alone then the radix tree is sufficient to establish the order of pages
> in a mapping. The only problem is to get an array of pointers to a
> sequence of pages together by reading through the radix tree. I do not
> know what else would be needed.

No. We have avoided fragmentation up until now. We avoid fragmentation like
the plague because it is crap. What _I_ do not want to do is add some
patches that make it work a bit better and everyone think's that's a signal
that it is a good idea to start using higher order allocations wherever
possible.

--
SUSE Labs, Novell Inc.