Re: [RFC] CMA page migration failure due to buffers on bh_lru

[Gioh Kim]

Hi,Laura.

I have a question.

Does the __evict_bh_lru() not need bh_lru_lock()?
The get_cpu_var() has already preenpt_disable() and can prevent other thread.
But get_cpu_var cannot prevent IRQ context such like page-fault.
I think if a page-fault occured and a file is read in IRQ context it can change cpu-lru.

Is my concern correct?


2014-06-30 ìì 4:49, Laura Abbott ì ê:
> (cc-ing Hugh since he had comments on the patch before)
>
> On 6/26/2014 4:23 PM, Gioh Kim wrote:
> > 2014-06-27 ìì 12:57, Michal Nazarewicz ì ê:
> > > On Tue, Jun 24 2014, Gioh Kim <gioh.kim@xxxxxxx> wrote:
> > > > Hello,
> > > >
> > > > I am trying to apply CMA feature for my platform.
> > > > My kernel version, 3.10.x, is not allocating memory from CMA area so that I applied
> > > > a Joonsoo Kim's patch (https://lkml.org/lkml/2014/5/28/64).
> > > > Now my platform can use CMA area effectively.
> > > >
> > > > But I have many failures to allocate memory from CMA area.
> > > > I found the same situation to Laura Abbott's patch descrbing,
> > > > https://lkml.org/lkml/2012/8/31/313,
> > > > that releases buffer-heads attached at CPU's LRU list.
> > > >
> > > > If Joonsoo's patch is applied and/or CMA feature is applied more and more,
> > > > buffer-heads problem is going to be serious definitely.
> > > >
> > > > Please look into the Laura's patch again.
> > > > I think it must be applied with Joonsoo's patch.
> > >
> > > Just to make sure I understood you correctly, you're saying Laura's
> > > patch at <https://lkml.org/lkml/2012/8/31/313> fixes your issue?
> >
> > Yes, it is.
>
> I submitted this before and it was suggested that this was more
> related to filesystems
>
> http://marc.info/?l=linaro-mm-sig&m=137645770708817&w=2
>
> I never saw more discussion and pushed this into the 'CMA hacks' pile.
> So far we've been keeping the patch out of tree and it's useful to know
> that others have found the same problem. I'm willing to resubmit the
> patch for further discussion.
>
> Thanks,
> Laura
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