Re: [PATCH/RFC] Simplified Readahead

Nick Piggin
2004-09-24T16:40:39Z

Steven Pratt wrote:
> Andrew Morton wrote:
>
>> Steven Pratt <slpratt@austin.ibm.com> wrote:
>>
>>
>>> would like to offer up an alternative simplified design which will
>>> not only make the code easier to maintain,
>>>
>>
>>
>> We won't know that until all functionality is in place.
>>
>>
> Ok, but both you and Nick indicated that the queue congestion isn't
> needed,

I would have thought that always doing the readahead would provide a
more graceful degradation, assuming the readahead algorithm is fairly
accurate, and copes with things like readahead thrashing (which we
hope is the case).

>> I do think we should skip the I/O for POSIX_FADV_WILLNEED against a
>> congested queue. I can't immediately think of a good reason for skipping
>> the I/O for normal readahead.
>>

I don't see why you should skip the readahead for FADVISE_WILLNEED
either. Presumably if someone needs this, they really need it. We
should aim for optimal behaviour when the apis are being used correctly...