On Thu 06-09-18 11:13:42, Aneesh Kumar K.V wrote: > Current code doesn't do page migration if the page allocated is a compound page. > With HugeTLB migration support, we can end up allocating hugetlb pages from > CMA region. Also THP pages can be allocated from CMA region. This patch updates > the code to handle compound pages correctly. > > This use the new helper get_user_pages_cma_migrate. It does one get_user_pages > with right count, instead of doing one get_user_pages per page. That avoids > reading page table multiple times. > > The patch also convert the hpas member of mm_iommu_table_group_mem_t to a union. > We use the same storage location to store pointers to struct page. We cannot > update alll the code path use struct page *, because we access hpas in real mode > and we can't do that struct page * to pfn conversion in real mode. I am not fmailiar with this code so bear with me. I am completely missing the purpose of this patch. The changelog doesn't really explain that AFAICS. I can only guess that you do not want to establish long pins on CMA pages, right? So whenever you are about to pin a page that is in CMA you migrate it away to a different !__GFP_MOVABLE page, right? If that is the case then how do you handle pins which are already in zone_movable? I do not see any specific check for those. Btw. why is this a proper thing to do? Problems with longterm pins are not only for CMA/ZONE_MOVABLE pages. Pinned pages are not reclaimable as well so there is a risk of OOMs if there are too many of them. We have discussed approaches that would allow to force pin invalidation/revocation at LSF/MM. Isn't that a more appropriate solution to the problem you are seeing? -- Michal Hocko SUSE Labs
