Re: [RFC, patch 1/2] Allow up to 1GB logs in mkfs.xfs

[Lachlan McIlroy <lachlan@sgi.com>]

Mark Goodwin wrote:
> 
> David Chinner wrote:
>> On Fri, Feb 22, 2008 at 04:44:02PM +1100, Lachlan McIlroy wrote:
>>> David Chinner wrote:
>>>> On Fri, Feb 22, 2008 at 01:44:38PM +1100, Niv Sardi wrote:
>>>>> David Chinner <dgc@sgi.com> writes:
>>>>>> Increase the maximum log size supported by mkfs.
>>>> ....
>>>>>> Hence logs larger than 2^30 will not work without kernel
>>>>>> modifications.
>> Therefore this change is limited to increasing the
>>>>>> log size to what we can currently support in kernel space with
>>>>>> needing kernel modifications.
> 
> Does anyone know of any work in mainline to address this?
> 
>>>>> I'm glad you got time to get around this, I didn't include it in the
>>>>> first batch as I was told it 'broke things'.
>>>> Right. There's all sorts of nasties lurking if we go over 1GB in
>>>> size, but AFAICT up to 1GB is OK. There's still lots of validation
>>>> needing to be done - that's why this is an "RFC" and not something
>>>> ready for checkin yet. That's where more eye's and testers are
>>>> handy...
>>> Dave, have you run any tests to see if we get any speed-ups with
>>> this change?
>>
>> Not yet - I've been running it through QA with different log sizes
>> first to see if there's anything obviously broken with the kernel
>> w.r.t. larger log sizes (nothing wrong so far).
> 
> What sort of improvements are we expecting? Log bound benchmarks will
> tail-push later than they do now, wont they? Which particular benchmarks
> are you thinking of running?
> 

Does a larger on-disk log mean we can have a lot more items in the AIL?