Messages in this thread | | | Date | Wed, 21 Apr 2010 16:13:59 -0400 | From | Phillip Susi <> | Subject | Re: readahead on directories |
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On 4/21/2010 4:01 PM, Jamie Lokier wrote: > Ok, this discussion has got a bit confused. Text above refers to > needing to asynchronously read next block in a directory, but if they > are small then that's not important.
It is very much important since if you ready each small directory one block at a time, it is very slow. You want to queue up reads to all of them at once so they can be batched.
> FIEMAP suggestion is only if you think you need to issue reads for > multiple blocks in the _same_ directory in parallel. From what you say, > I doubt that's important.
That may be why you suggested it, but it is also exactly what readahead() does. It also queues the read asynchronously which is what I really want so that I can queue more reads on other directories in one big batch.
> That was my first suggestion: threads with readdir(); I thought it had > been rejected hence the further discussion.
Yes, it was sort of rejected, which is why I said it's just a workaround for now until readahead() works on directories. It will produce the desired IO pattern but at the expense of ram and cpu cycles creating a bunch of short lived threads that go to sleep almost immediately after being created, and exit when they wake up. readahead() would be much more efficient.
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