Hello, On Monday, October 10, 2011 2:08 PM Maxime Coquelin wrote: > On 10/06/2011 03:54 PM, Marek Szyprowski wrote: > > Welcome everyone again, > > > > Once again I decided to post an updated version of the Contiguous Memory > > Allocator patches. > > > > This version provides mainly a bugfix for a very rare issue that might > > have changed migration type of the CMA page blocks resulting in dropping > > CMA features from the affected page block and causing memory allocation > > to fail. Also the issue reported by Dave Hansen has been fixed. > > > > This version also introduces basic support for x86 architecture, what > > allows wide testing on KVM/QEMU emulators and all common x86 boxes. I > > hope this will result in wider testing, comments and easier merging to > > mainline. > > > > I've also dropped an examplary patch for s5p-fimc platform device > > private memory declaration and added the one from real life. CMA device > > private memory regions are defined for s5p-mfc device to let it allocate > > buffers from two memory banks. > > > > ARM integration code has not been changed since last version, it > > provides implementation of all the ideas that has been discussed during > > Hello Marek, > > We are currently testing CMA (v16) on Snowball platform. > This feature is very promising, thanks for pushing it! > > During our stress tests, we encountered some problems : > > 1) Contiguous allocation lockup: > When system RAM is full of Anon pages, if we try to allocate a > contiguous buffer greater than the min_free value, we face a > dma_alloc_from_contiguous lockup. > The expected result would be dma_alloc_from_contiguous() to fail. > The problem is reproduced systematically on our side. Thanks for the report. Do you use Android's lowmemorykiller? I haven't tested CMA on Android kernel yet. I have no idea how it will interfere with Android patches. > > 2) Contiguous allocation fail: > We have developed a small driver and a shell script to > allocate/release contiguous buffers. > Sometimes, dma_alloc_from_contiguous() fails to allocate the > contiguous buffer (about once every 30 runs). > We have 270MB Memory passed to the kernel in our configuration, > and the CMA pool is 90MB large. > In this setup, the overall memory is either free or full of > reclaimable pages. Yeah. We also did such stress tests recently and faced this issue. I've spent some time investigating it but I have no solution yet. The problem is caused by a page, which is put in the CMA area. This page is movable, but it's address space provides no 'migratepage' method. In such case mm subsystem uses fallback_migrate_page() function. Sadly this function only returns -EAGAIN. The migration loops a few times over it and fails causing the fail in the allocation procedure. We are investing now which kernel code created/allocated such problematic pages and how to add real migration support for them. > For now, we didn't had time to investigate further theses problems. > Have you already faced this kind of issues? > Could someone testing CMA on other boards confirm/infirm theses > problems? Best regards -- Marek Szyprowski Samsung Poland R&D Center -- 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/ . Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/ Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>