Re: Random file I/O regressions in 2.6
From: Andrew Morton
Date: Mon May 10 2004 - 18:12:39 EST
Ram Pai <linuxram@xxxxxxxxxx> wrote:
> I am nervous about this change. You are totally getting rid of
> lazy-readahead and that was the optimization which gave the best
> possible boost in performance.
Because it disabled the large readahead outside the area which the app is
reading. But it's still reading too much.
> Let me see how this patch does with a DSS benchmark.
That was not a real patch. More work is surely needed to get that right.
> In the normal large random workload this extra page would have
> compesated for all the wasted readaheads.
I disagree that 64k is "normal"!
> However in the case of
> sysbench with Andrew's ra-copy patch the readahead calculation is not
> happening quiet right. Is it worth trying to get a marginal gain
> with sysbench at the cost of getting a big hit on DSS benchmarks,
> aio-tests,iozone and probably others. Or am I making an unsubstantiated
> claim? I will get back with results.
It shouldn't hurt at all - the app does a seek, we perform the
As I say, my main concern is that we correctly transition from seeky access
to linear access and resume readahead.
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