On 02/23/2016 07:33 PM, Kirill A. Shutemov wrote: > On Tue, Feb 23, 2016 at 06:45:05PM +0530, Anshuman Khandual wrote: >> Not able to understand the first code block of follow_page_mask >> function. follow_huge_addr function is expected to find the page >> struct for the given address if it turns out to be a HugeTLB page >> but then when it finds the page we bug on if it had been called >> with FOLL_GET flag. >> >> page = follow_huge_addr(mm, address, flags & FOLL_WRITE); >> if (!IS_ERR(page)) { >> BUG_ON(flags & FOLL_GET); >> return page; >> } >> >> do_move_page_to_node_array calls follow_page with FOLL_GET which >> in turn calls follow_page_mask with FOLL_GET. On POWER, the >> function follow_huge_addr is defined and does not return -EINVAL >> like the generic one. It returns the page struct if its a HugeTLB >> page. Just curious to know what is the purpose behind the BUG_ON. > > I would guess requesting pin on non-reclaimable page is considered > useless, meaning suspicius behavior. BUG_ON() is overkill, I think. > WARN_ON_ONCE() would make it.
pin on non-reclaimable page ? I thought the page reference is obtained for page migration purpose only. I may be missing something here. > > Not that this follow_huge_addr() on Power is not reachable via > do_move_page_to_node_array(), because the vma is !vma_is_migratable(). Was experimenting with that enabled via ARCH_ENABLE_HUGEPAGE_MIGRATION. _______________________________________________ Linuxppc-dev mailing list Linuxppc-dev@lists.ozlabs.org https://lists.ozlabs.org/listinfo/linuxppc-dev