Hello, Ивайло On Tue, Oct 29, 2013 at 02:47:35PM +0200, Ивайло Димитров wrote: > > Hi, > > > >-------- Оригинално писмо -------- > >От: Minchan Kim > >Относно: Re: OMAPFB: CMA allocation failures > >До: Ивайло Димитров > >Изпратено на: Понеделник, 2013, Октомври 28 09:37:48 EET > > > > > >Hello, > > > >On Tue, Oct 15, 2013 at 09:49:51AM +0300, Ивайло Димитров wrote: > >> Hi > >> > >> >-------- Оригинално писмо -------- > >> >От: Tomi Valkeinen > >> >Относно: Re: OMAPFB: CMA allocation failures > >> >До: Ивайло Димитров > >> > >> >Изпратено на: Понеделник, 2013, Октомври 14 09:04:35 EEST > >> > > >> > > >> >Hi, > >> > > >> >On 12/10/13 17:43, Ивайло Димитров wrote: > >> >> Hi Tomi, > >> >> > >> >> patch http://lists.infradead.org/pipermail/linux-arm-kernel/2012-November/131269.html modifies > >> >> omapfb driver to use DMA API to allocate framebuffer memory instead of preallocating VRAM. > >> >> > >> >> With this patch I see a lot of: > >> >> > >> >> Jan 1 06:33:27 Nokia-N900 kernel: [ 2054.879577] cma: dma_alloc_from_contiguous(cma c05f5844, count 192, align 8) > >> >> Jan 1 06:33:27 Nokia-N900 kernel: [ 2054.914215] cma: dma_alloc_from_contiguous(): memory range at c07df000 is busy, retrying > >> >> Jan 1 06:33:27 Nokia-N900 kernel: [ 2054.933502] cma: dma_alloc_from_contiguous(): memory range at c07e1000 is busy, retrying > >> >> Jan 1 06:33:27 Nokia-N900 kernel: [ 2054.940032] cma: dma_alloc_from_contiguous(): memory range at c07e3000 is busy, retrying > >> >> Jan 1 06:33:27 Nokia-N900 kernel: [ 2054.966644] cma: dma_alloc_from_contiguous(): memory range at c07e5000 is busy, retrying > >> >> Jan 1 06:33:27 Nokia-N900 kernel: [ 2054.976867] cma: dma_alloc_from_contiguous(): memory range at c07e7000 is busy, retrying > >> >> Jan 1 06:33:27 Nokia-N900 kernel: [ 2055.038055] cma: dma_alloc_from_contiguous(): memory range at c07e9000 is busy, retrying > >> >> Jan 1 06:33:27 Nokia-N900 kernel: [ 2055.038116] cma: dma_alloc_from_contiguous(): returned (null) > >> >> Jan 1 06:33:27 Nokia-N900 kernel: [ 2055.038146] omapfb omapfb: failed to allocate framebuffer > >> >> > >> >> errors while trying to play a video on N900 with Maemo 5 (Fremantle) on top of linux-3.12rc1. > >> >> It is deffinitely the CMA that fails to allocate the memory most of the times, but I wonder > >> >> how reliable CMA is to be used in omapfb. I even reserved 64MB for CMA, but that made no > >> >> difference. If CMA is disabled, the memory allocation still fails as obviously it is highly > >> >> unlikely there will be such a big chunk of continuous free memory on RAM limited device like > >> >> N900. > >> >> > >> >> One obvious solution is to just revert the removal of VRAM memory allocator, but that would > >> >> mean I'll have to maintain a separate tree with all the implications that brings. > >> >> > >> >> What would you advise on how to deal with the issue? > >> > > >> >I've not seen such errors, and I'm no expert on CMA. But I guess the > >> >contiguous memory area can get fragmented enough no matter how hard one > >> >tries to avoid it. The old VRAM system had the same issue, although it > >> >was quite difficult to hit it. > >> > >> I am using my n900 as a daily/only device since the beginning of 2010, never seen such an > >> issue with video playback. And as a maintainer of one of the community supported kernels for > >> n900 (kernel-power) I've never had such an issue reported. On stock kernel and derivatives of > >> course. It seems VRAM allocator is virtually impossible to fail, while with CMA OMAPFB fails on > >> the first video after boot-up. > >> > >> When saying you've not seen such an issue - did you actually test video playback, on what > >> device and using which distro? Did you use DSP accelerated decoding? > >> > >> >64MB does sound quite a lot, though. I wonder what other drivers are > >> >using CMA, and how do they manage to allocate so much memory and > >> >fragment it so badly... With double buffering, N900 should only need > >> >something like 3MB for the frame buffer. > >> > >> Sure, 64 MB is a lot, but I just wanted to see if that would make any difference. And for 720p > >> 3MB is not enough, something like 8MB is needed. > >> > >> >With a quick glance I didn't find any debugfs or such files to show > >> >information about the CMA area. It'd be helpful to find out what's going > >> >on there. Or maybe normal allocations are fragmenting the CMA area, but > >> >for some reason they cannot be moved? Just guessing. > >> > >> I was able to track down the failures to: > >> http://lxr.free-electrons.com/source/mm/migrate.c#L320 > > > >That path is for anonymous page migration so the culprit I can think of > >is that you did get_user_pages on those anonymous pages for pin them. > >Right? > > > > I grepped through the code and there are lots of places where get_user_pages is called, though > I suspect either SGX or DSP (or both) drivers to be the ones to blame. Both of them are active > and needed for HW accelerated video decoding. > > >If so, it's no surpse that fails the migration and CMA doesn't work. > > > >-- > >Kind regards, > >Minchan Kim > > > > Well, if CMA is to be reliable, I would expect some logic to take care about get_user_pages First of all, CMA is never reliable. > causing MIGRATE_CMA pages to be effectively made non-migratable, either by migrating them out of > CMA area before they got pinned or by providing a mechanism to migrate them when needed. I am far > from knowing the nuts and bolts of MM and CMA, but so far I failed to see any such logic. Without If you read below links you attached, you could know why it doesn't accept. > it, CMA could be fine for allocating small buffers, but when we talk about framebuffer memory > needed for 720p playback(for example) on a RAM limited embedded device, it is too fragile, IMO. True. > > BTW quick googling shows I am not the first one to encounter similar problems [0], [1], I don't > see solution for. > > However, back to omapfb - my understanding is that the way it uses CMA (in its current form) is > prone to allocation failures way beyond acceptable. Basically, fragile subsystem shouldn't use CMA, otherwise, your platform should support process killing to unpin some pages, Yeah I know it's not 100% solution and very horrible but I know some insane people have done it. I just post an idea. http://marc.info/?l=linux-mm&m=138311160522311&w=2 If anybody has a interest, maybe we will move that way. Thanks. > > Tomi, what do you think about adding module parameters to allow pre-allocating framebuffer memory > from CMA during boot? Or re-implement VRAM allocator to use CMA? As a good side-effect > OMAPFB_GET_VRAM_INFO will no longer return fake values. > > Regards, > Ivo > > [0] http://lwn.net/Articles/541423/ > [1] https://lkml.org/lkml/2012/11/29/69 > > -- > To unsubscribe, send a message with 'unsubscribe linux-mm' in > the body to majordomo@xxxxxxxxx. For more info on Linux MM, > see: http://www.linux-mm.org/ . > Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a> -- Kind regards, Minchan Kim -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>