Re: [00/17] Large Blocksize Support V3

[Nick Piggin]

Christoph Lameter wrote:
> On Thu, 26 Apr 2007, Nick Piggin wrote:
>
>
> > No I don't want to add another fs layer.
>
>
> Well maybe you could explain what you want. Preferably without redefining 
> the established terms?

Support for larger buffers than page cache pages.


> > I still don't think anti fragmentation or defragmentation are a good
> > approach, when you consider the alternatives.
>
>
> I have not heard of any alternatives in this discussion here. Just the old 
> line of lets tune the VM here and there and hope it lasts a while longer.

I didn't realise that one was even in the running. How can you "tune" the
VM to handle bigger block sizes?


> > OK, I would like to see them. And also discussions of things like why
> > we shouldn't increase PAGE_SIZE instead.
>
>
> Because 4k is a good page size that is bound to the binary format? Frankly 
> there is no point in having my text files in large page sizes. However, 
> when I read a dvd then I may want to transfer 64k chunks or when use my 
> flash drive I may want to transfer 128k chunks. And yes if a scientific 
> application needs to do data dump then it should be able to use very high 
> page sizes (megabytes, gigabytes) to be able to continue its work while 
> the huge dumps runs at full I/O speed ...

So block size > page cache size... also, you should obviously be using
hardware that is tuned to work well with 4K pages, because surely there
is lots of that around.

--
SUSE Labs, Novell Inc.
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