Let's also CC Marek On Thu 01-12-16 08:43:40, Vlastimil Babka wrote: > On 12/01/2016 08:21 AM, Michal Hocko wrote: > > Forgot to CC Joonsoo. The email thread starts more or less here > > http://lkml.kernel.org/r/20161130092239.gd18...@dhcp22.suse.cz > > > > On Thu 01-12-16 08:15:07, Michal Hocko wrote: > > > On Wed 30-11-16 20:19:03, Robin H. Johnson wrote: > > > [...] > > > > alloc_contig_range: [83f2a3, 83f2a4) PFNs busy > > > > > > Huh, do I get it right that the request was for a _single_ page? Why do > > > we need CMA for that? > > Ugh, good point. I assumed that was just the PFNs that it failed to migrate > away, but it seems that's indeed the whole requested range. Yeah sounds some > part of the dma-cma chain could be smarter and attempt CMA only for e.g. > costly orders.
Is there any reason why the DMA api doesn't try the page allocator first before falling back to the CMA? I simply have a hard time to see why the CMA should be used (and fragment) for small requests size. -- Michal Hocko SUSE Labs