Hello, On Tuesday, October 11, 2011 9:30 AM Maxime Coquelin wrote: > On 10/11/2011 09:17 AM, Marek Szyprowski wrote: > > On Monday, October 10, 2011 2:08 PM Maxime Coquelin wrote: > > > > 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. > > > > The software used for this test (v16) is a generic 3.0 Kernel and a > minimal filesystem using Busybox. I'm really surprised. Could you elaborate a bit how to trigger this issue? I've did several tests and I never get a lockup. Allocation failed from time to time though. > With v15 patchset, I also tested it with Android. > IIRC, sometimes the lowmemorykiller succeed to get free space and the > contiguous allocation succeed, sometimes we faced the lockup. > > >> 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 s/investing/investigating > > pages and how to add real migration support for them. > > > > Ok, thanks for pointing this out. We found this issue very recently. I'm still surprised that we did not notice it during system testing. 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>