Messages in this thread | | | Date | Fri, 02 Jun 2006 12:39:37 +1000 | From | Nick Piggin <> | Subject | Re: [rfc][patch] remove racy sync_page? |
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Nick Piggin wrote: > Linus Torvalds wrote: > >> >> On Thu, 1 Jun 2006, Nick Piggin wrote: >> >>> If this wasn't clear: I don't mean per-task plugs as in "the task >>> explicitly plugs and unplugs the block device"[*]; I mean really >>> per-task plugs. >> >> >> >> That would be insane. It would mean that you'd have to unplug whether you > > > I don't think it is. > >> wanted to or not. Ie you've now made "sys_readahead()" impossible to >> do well, and doing read-ahead across multiple files. > > > Now it is you who are ignoring what I've been saying. I've been saying > that I don't think your sys_readahead examples have had much to do with > plugging: > > 1. If there are no other requests to seek to, plugging doesn't matter; > 2. If there are other requests to seek to, the queue won't be plugged > or will soon become unplugged anyway. So the current system isn't > somehow going to do the right thing every time and be immune to > seeking.
Lastly, an app can still issue multiple sys_readaheads and still get seek protection -- it isn't like disks have suddenly got faster than CPUs overnight.
as-iosched.c can handle the case where a request goes out to disk, and later a new one comes in nearby (deadline IIRC isn't good at this unfortunately, nor does it seek backwards)
OTOH, if you're using as-iosched.c, you explicitly get a good amount of seek protection anyway.
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