On 04/17/2018 04:36 AM, Michal Hocko wrote:
On Fri 26-01-18 02:08:14, Laura Abbott wrote:CMA as it's currently designed requires alignment to the pageblock size c.f. /* * Sanitise input arguments. * Pages both ends in CMA area could be merged into adjacent unmovable * migratetype page by page allocator's buddy algorithm. In the case, * you couldn't get a contiguous memory, which is not what we want. */ alignment = max(alignment, (phys_addr_t)PAGE_SIZE << max_t(unsigned long, MAX_ORDER - 1, pageblock_order)); On arm64 with 64K page size and transparent huge page, this gives an alignment of 512MB. This is quite restrictive and can eat up significant portions of memory on smaller memory targets. Adjusting the configuration options really isn't ideal for distributions that aim to have a single image which runs on all targets. Approaches I've thought about: - Making CMA alignment less restrictive (and dealing with the fallout from the comment above) - Command line option to force a reasonable alignmentLaura, are you still interested discussing this or other CMA related topic?
In light of Joonsoo's patches, I don't think we need a lot of time but I'd still like some chance to discuss. I think there was some other interest in CMA topics so it can be combined with those if they are happening as well. Thanks, Laura
