Messages in this thread | | | Subject | Re: Drastic Slowdown of 'fseek()' Calls From 2.4 to 2.6 -- VMM Change? | From | Arjan van de Ven <> | Date | Sun, 26 Feb 2006 15:11:20 +0100 |
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On Mon, 2006-02-27 at 00:50 +1100, Nick Piggin wrote: > > Not really. The app is not silly if it does an fseek() then a _write_. > Writing page sized and aligned chunks should not require previously > uptodate pagecache, so doing a pre-read like this is a complete waste. > > Actually glibc tries to turn this pre-read off if the seek is to a page > aligned offset, presumably to handle this case. However a big write > would only have to RMW the first and last partial pages, so pre-reading > 128KB in this case is wrong. > > And I would also say a 4K read is wrong as well, because a big read will > be less efficient due to the extra syscall and small IO.
I can very much see the point of issuing a sys_readahead instead.....
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