Messages in this thread | | | Date | Wed, 16 Jul 2003 14:46:56 +0200 | From | Jens Axboe <> | Subject | Re: RFC on io-stalls patch |
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On Wed, Jul 16 2003, Andrea Arcangeli wrote: > On Tue, Jul 15, 2003 at 01:27:37PM +0200, Jens Axboe wrote: > > On Tue, Jul 15 2003, Alan Cox wrote: > > > On Maw, 2003-07-15 at 06:26, Jens Axboe wrote: > > > > Sorry, but I think that is nonsense. This is the way we have always > > > > worked. You just have to maintain a decent queue length still (like we > > > > always have in 2.4) and there are no problems. > > > > > > The memory pinning problem is still real - and always has been. It shows up > > > best not on IDE disks but large slow media like magneto opticals where you > > > can queue lots of I/O but you get 500K/second > > > > Not the same thing. On slow media, like dvd-ram, what causes the problem > > is that you can dirty basically all of the RAM in the system. That has > > nothing to do with memory pinned in the request queue. > > you can trivially bound the amount of dirty memory to nearly 0% with the > bdflush sysctl. And the overkill size of the queue until pre3 could be > an huge VM overhead compared to the dirty memory on lowmem boxes, > example a 32/64M machine. So I disagree it's only a mistake of write > throttling that gives problems on slow media. > > Infact I tend to think the biggest problem for slow media in 2.4 is the > lack of per spindle pdflush.
Well it's a combined problem. Threshold too high on dirty memory, someone doing a read well get stuck flushing out as well.
-- Jens Axboe
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