Yasunori Goto <y-goto@xxxxxxxxxxxxxx> writes: > > However, I think this has the possibility of a finishing blow of OOM. > For example, > > 1) Page caches occupy normal zone, and DMA zone is free. > 2) A user's application requires a few GB memory and mlock it. > All DMA zone is occupied by it. The VM has special "lower zone protection" to protect against these kinds of deadlocks. They can be circumvented, but it takes effort. > 3) A device which allows over 4GB is hot-added. > But dma_alloc_coherent() try to allocate DMA zone. > Then OOM occurs because there is no freeable pages. > > I heard there are some users who require a few GB mlock. Normally mlock is limited to half the memory exactly to avoid such problems. Also I believe there are some issues with non continuous memory on some IA64 systems -- e.g. Altixes iirc have the requirement that you use the IOMMU for higher memory. So it's probably not easy to change. -Andi -- ak@xxxxxxxxxxxxxxx -- To unsubscribe from this list: send the line "unsubscribe linux-ia64" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
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