On 09/06/2016 11:57 AM, Balbir Singh wrote: > > When PCI Device pass-through is enabled via VFIO, KVM-PPC will > pin pages using get_user_pages_fast(). One of the downsides of > the pinning is that the page could be in CMA region. The CMA > region is used for other allocations like the hash page table. > Ideally we want the pinned pages to be from non CMA region. > > This patch (currently only for KVM PPC with VFIO) forcefully > migrates the pages out (huge pages are omitted for the moment). > There are more efficient ways of doing this, but that might > be elaborate and might impact a larger audience beyond just > the kvm ppc implementation. > > The magic is in new_iommu_non_cma_page() which allocates the > new page from a non CMA region. > > I've tested the patches lightly at my end. The full solution > requires migration of THP pages in the CMA region. That work > will be done incrementally on top of this. > > Previous discussion was at > http://permalink.gmane.org/gmane.linux.kernel.mm/136738 > > Cc: Benjamin Herrenschmidt <benh@xxxxxxxxxxxxxxxxxxx> > Cc: Michael Ellerman <mpe@xxxxxxxxxxxxxx> > Cc: Paul Mackerras <paulus@xxxxxxxxxx> > Cc: Alexey Kardashevskiy <aik@xxxxxxxxx> > > Signed-off-by: Balbir Singh <bsingharora@xxxxxxxxx> > Acked-by: Alexey Kardashevskiy <aik@xxxxxxxxx> > --- > arch/powerpc/include/asm/mmu_context.h | 1 + > arch/powerpc/mm/mmu_context_iommu.c | 81 ++++++++++++++++++++++++++++++++-- > 2 files changed, 78 insertions(+), 4 deletions(-) > > diff --git a/arch/powerpc/include/asm/mmu_context.h b/arch/powerpc/include/asm/mmu_context.h > index 9d2cd0c..475d1be 100644 > --- a/arch/powerpc/include/asm/mmu_context.h > +++ b/arch/powerpc/include/asm/mmu_context.h > @@ -18,6 +18,7 @@ extern void destroy_context(struct mm_struct *mm); > #ifdef CONFIG_SPAPR_TCE_IOMMU > struct mm_iommu_table_group_mem_t; > > +extern int isolate_lru_page(struct page *page); /* from internal.h */ Small nit, cant we just add "mm/internal.h" header here with full path ? > extern bool mm_iommu_preregistered(void); > extern long mm_iommu_get(unsigned long ua, unsigned long entries, > struct mm_iommu_table_group_mem_t **pmem); > diff --git a/arch/powerpc/mm/mmu_context_iommu.c b/arch/powerpc/mm/mmu_context_iommu.c > index da6a216..e0f1c33 100644 > --- a/arch/powerpc/mm/mmu_context_iommu.c > +++ b/arch/powerpc/mm/mmu_context_iommu.c > @@ -15,6 +15,9 @@ > #include <linux/rculist.h> > #include <linux/vmalloc.h> > #include <linux/mutex.h> > +#include <linux/migrate.h> > +#include <linux/hugetlb.h> > +#include <linux/swap.h> > #include <asm/mmu_context.h> > > static DEFINE_MUTEX(mem_list_mutex); > @@ -72,6 +75,55 @@ bool mm_iommu_preregistered(void) > } > EXPORT_SYMBOL_GPL(mm_iommu_preregistered); > > +/* > + * Taken from alloc_migrate_target with changes to remove CMA allocations > + */ > +struct page *new_iommu_non_cma_page(struct page *page, unsigned long private, > + int **resultp) > +{ > + gfp_t gfp_mask = GFP_USER; > + struct page *new_page; > + > + if (PageHuge(page) || PageTransHuge(page) || PageCompound(page)) > + return NULL; > + > + if (PageHighMem(page)) > + gfp_mask |= __GFP_HIGHMEM; > + > + /* > + * We don't want the allocation to force an OOM if possibe > + */ > + new_page = alloc_page(gfp_mask | __GFP_NORETRY | __GFP_NOWARN); So what guarantees that the new page too wont come from MIGRATE_CMA page block ? Is absence of __GFP_MOVABLE flag enough. Also should not we be checking that migrate type of the new allocated page is indeed not MIGRATE_CMA ? -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
