Messages in this thread | | | Date | Tue, 30 May 2006 11:05:49 +0200 | From | Jens Axboe <> | Subject | Re: [rfc][patch] remove racy sync_page? |
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On Mon, May 29 2006, Andrew Morton wrote: > On Tue, 30 May 2006 12:54:53 +1000 > Nick Piggin <nickpiggin@yahoo.com.au> wrote: > > > Andrew Morton wrote: > > > > >On Tue, 30 May 2006 10:08:06 +1000 > > >Nick Piggin <nickpiggin@yahoo.com.au> wrote: > > > > > > > > >>Which is what I want to know. I don't exactly have an interesting > > >>disk setup. > > >> > > > > > >You don't need one - just a single disk should show up such problems. I > > >forget which workloads though. Perhaps just a linear read (readahead > > >queues the I/O but doesn't unplug, subsequent lock_page() sulks). > > > > > > > I guess so. Is plugging still needed now that the IO layer should > > get larger requests? Disabling it might result in a small initial > > request (although even that may be good for pipelining)... > > Mysterious question, that. A few years ago I think Jens tried pulling > unplugging out, but some devices still want it (magneto-optical > storage iirc). And I think we did try removing it, and it caused > hurt.
I did, back when we had problems due to the blk_plug_lock being a global one. I first wanted to investigate if plugging still made a difference, otherwise we could've just ripped it out back than and the problem would be solved. But it did get us about a 10% boost on normal SCSI drives (don't think I tested MO drives at all), so it was fixed up.
> > sync_page wants to get either the current mapping, or a NULL one. > > The sync_page methods must then be able to handle running into a > > NULL mapping. > > > > With splice, the mapping can change, so you can have the wrong > > sync_page callback run against the page. > > Oh.
Maybe I'm being dense, but I don't see a problem there. You _should_ call the new mapping sync page if it has been migrated.
> > >>Well yes, writing to a page would be the main reason to set it dirty. > > >>Is splice broken as well? I'm not sure that it always has a ref on the > > >>inode when stealing a page. > > >> > > > > > >Whereabouts? > > > > > > > The ->pin() calls in pipe_to_file and pipe_to_sendpage? > > One for Jens...
splice never incs/decs any inode related reference counts, so if it needs to then yes it's broken. Any references to kernel code that deals with that?
-- Jens Axboe
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