Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> writes: > On Tue, 8 Jan 2019 10:21:06 +0530 "Aneesh Kumar K.V" <aneesh.kumar@xxxxxxxxxxxxx> wrote: > >> ppc64 use CMA area for the allocation of guest page table (hash page table). We won't >> be able to start guest if we fail to allocate hash page table. We have observed >> hash table allocation failure because we failed to migrate pages out of CMA region >> because they were pinned. This happen when we are using VFIO. VFIO on ppc64 pins >> the entire guest RAM. If the guest RAM pages get allocated out of CMA region, we >> won't be able to migrate those pages. The pages are also pinned for the lifetime of the >> guest. >> >> Currently we support migration of non-compound pages. With THP and with the addition of >> hugetlb migration we can end up allocating compound pages from CMA region. This >> patch series add support for migrating compound pages. The first path adds the helper >> get_user_pages_cma_migrate() which pin the page making sure we migrate them out of >> CMA region before incrementing the reference count. > > Does this code do anything for architectures other than powerpc? If > not, should we be adding the ifdefs to avoid burdening other > architectures with unused code? Any architecture enabling CMA may need this. I will move most of this below CONFIG_CMA. -aneesh
