On 06/09/16 21:54, Anshuman Khandual wrote: > 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 ? > I did not think it was worth including it here >> 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. I think so, that is what I am relying on and checked for Also should not > we be checking that migrate type of the new allocated page is indeed > not MIGRATE_CMA ? > I don't think that is required, may be I can do a VM_WARN_ON for debugging Balbir Singh. -- 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
