On Tue 17-04-18 08:01:53, Laura Abbott wrote: > 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 alignment > > > > Laura, 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. OK, so I've put a placeholder for a CMA discussion. You have won the lead on that session ;) We can change that later of course. -- Michal Hocko SUSE Labs
