Re: cfq misbehaving on 2.6.11-1.14_FC3

From: Jens Axboe
Date: Fri Jun 17 2005 - 13:16:59 EST

On Fri, Jun 17 2005, Andrea Arcangeli wrote:
> On Fri, Jun 17, 2005 at 04:10:40PM +0200, Jens Axboe wrote:
> > Perhaps rmap could be used to lookup who has a specific page mapped...
> I doubt, the computing and locking cost for every single page write
> would be probably too high. Doing it during swapping isn't a big deal
> since cpu is mostly idle during swapouts, but doing it all the time
> sounds a bit overkill.

We could cut the lookup down to per-request, it's not very likely that
seperate threads would be competing for the exact same disk location.
But it's still not too nice...

> A mechanism to pass down a pid would be much better. However I'm unsure
> where you could put the info while dirtying the page. If it was an uid
> it might be reasonable to have it in the address_space, but if you want
> a pid as index, then it'd need to go in the page_t, which would waste
> tons of space. Having a pid in the address space, may not work well with
> a database or some other app with multiple processes.

The previous patch just added a pid_t to struct page, but I knew all
along that this was just for testing, I never intended to merge that

Jens Axboe

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