Messages in this thread | | | Subject | Re: kernel BUG at lib/radix-tree.c:473! | From | Markus Armbruster <> | Date | Thu, 14 Aug 2008 18:48:36 -0400 |
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Jeremy Fitzhardinge <jeremy@goop.org> writes:
> Hugh Dickins wrote: >> As you can see, I'm still groping towards the right answer. >> The driver probably needs to provide its own backing_dev_info >> (or point to a suitable default), and its own address_space_ops, >> and perhaps more (there should be examples elsewhere). But whether >> it is actually wrong, or whether I was wrong to mess it up, I've >> not yet decided. >> > > My understanding is that the driver is doing something a bit clever: > it uses the page dirty flags to determine which parts of the > framebuffer have been written to, and uses that information to > minimize the amount of stuff that needs to be copied out. The writes
Yes.
> to the pages are not expected to generate actual page faults. > > But I haven't really looked at it closely, and I'm not at all familiar > with the vm at this layer. I'm not sure how it actually allocates the > framebuffer memory for example (vmalloc? incrementally on faults?).
vmalloc()
> I'm hoping Markus will leap in, since wrote this stuff. Or, gasp, > I'll read the code myself.
The actual cleverness is in fb_defio[*], which was written by Jaya Kumar (cc'ed). I merely ripped out the old, somewhat racy cleverness I inherited from Anthony Liguori (which you can still admire in Xen's 2.6.18 kernel), and switched over to use fb_defio instead. Because one instance of clever code is enough.
My understanding of fb_defio's inner workings is rather limited I fear. I'm just using it.
Jaya, could you help?
[...]
[*] Documentation/fb/deferred_io.txt drivers/video/fb_defio.c
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