On Tue, 2020-03-10 at 18:37 +0100, Michal Hocko wrote: > On Tue 10-03-20 10:25:59, Roman Gushchin wrote: > > Well, so far I was focused on a particular case when the target cma > > size > > is significantly smaller than the total RAM size (~5-10%). What is > > the right > > thing to do here? Fallback to the current behavior if the requested > > size is > > more than x% of total memory? 1/2? How do you think? > > I would start by excluding restricted kernel zones (<ZONE_NORMAL). > Cutting off 1G of ZONE_DMA32 might be a real problem. It looks like memblock_find_in_range_node(), which is called from memblock_alloc_range_nid(), will already do top-down allocation inside each node. However, looking at that code some more, it has some limitations that we might not want. Specifically, if we want to allocate for example a 16GB CMA area, but the node in question only has a 15GB available area in one spot and a 1GB available area in another spot, for example due to memory holes, the allocation will fail. I wonder if it makes sense to have separate cma_declare_contiguous calls for each 1GB page we set up. That way it will be easier to round-robin between the ZONE_NORMAL zones in each node, and also to avoid the ZONE_DMA32 and other special nodes on systems where those are a relatively small part of memory. I'll whip up a patch to do that. -- All Rights Reversed.
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