Re: [PATCH 4/8] fbdev: ssd1307fb: Use vmalloc to allocate video memory.

On 14/02/15 16:22, Thomas Niederprüm wrote:

Am Thu, 12 Feb 2015 16:11:21 +0100
schrieb Maxime Ripard [off-list ref]:

quoted

On Sat, Feb 07, 2015 at 04:35:41PM +0100, Thomas Niederprüm wrote:

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Am Sat, 7 Feb 2015 12:18:21 +0100
schrieb Maxime Ripard [off-list ref]:

quoted

Hi,

On Fri, Feb 06, 2015 at 11:28:10PM +0100, niederp@physik.uni-kl.de
wrote:

quoted

From: Thomas Niederprüm <redacted>

It makes sense to use vmalloc to allocate the video buffer
since it has to be page aligned memory for using it with mmap.

Please wrap your commit log at 80 chars.

I'll try to do so in future, sorry for that.

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It looks like there's numerous fbdev drivers using this
(especially since you copy pasted that code, without mentionning
it).

Yes, I should have mentioned that in the commit message. As
implicitly indicated in the cover letter the rvmalloc() and
rvfree() are copy pasted from the vfb driver. Honestly, I didn't
give this one too much thought. It seemed a viable solution to the
mmap problem. For a bit more history on that, see my comment below.

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That should be turned into an allocator so that drivers all get
this right.

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Also deffered io seems buggy in combination with kmalloc'ed
memory (crash on unloading the module).

And maybe that's the real issue to fix.

The problem is solved by using vmalloc ;)

Yep, but why do you need to mark the reserved pages?

...

As far as I understood mmaped memory is marked as userspace memory in
the page table and is therefore subject to swapping. The pages are
marked reserved to make clear that this memory can not be swapped and
thus lock the pages in memory. See discussions [0,1,2]. 

Why is it a problem if it is swapped? Only CPU uses the memory, as far
as I can see.

Also, isn't doing __pa() for the memory returned by vmalloc plain wrong?

What was the crash about when using kmalloc? It would be good to fix
defio, as I don't see why it should not work with kmalloced memory.

 Tomi