Balbir Singh <bsingharora@xxxxxxxxx> writes: > From: Balbir Singh <bsingharora@xxxxxxxxx> > Subject: [RESEND][v2][PATCH] KVM: PPC: Book3S HV: Migrate pinned pages out of CMA > > 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, but there might be bugs > For example if after lru_add_drain(), the page is not isolated > is this a BUG? > > 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> > --- > arch/powerpc/include/asm/mmu_context.h | 1 + > arch/powerpc/mm/mmu_context_iommu.c | 80 ++++++++++++++++++++++++++++++++-- > 2 files changed, 77 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 */ > 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..c18f742 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 +75,54 @@ 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; Doesn't a PageCompound check cover all ? > + > + 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); > + return new_page; > +} > + > +static int mm_iommu_move_page_from_cma(struct page *page) > +{ > + int ret; > + LIST_HEAD(cma_migrate_pages); > + > + /* Ignore huge pages for now */ > + if (PageHuge(page) || PageTransHuge(page) || PageCompound(page)) > + return -EBUSY; > + > + lru_add_drain(); I guess I asked this last time. Shouldn't this be lru_add_drain_all() ? What if the page is in other cpu's pagevec ? > + ret = isolate_lru_page(page); > + if (ret) > + get_page(page); /* Potential BUG? */ > + > + list_add(&page->lru, &cma_migrate_pages); Is that correct ? if we failed the isolate_lru_page(), can we be sure we are not on lru at all ? ie, what if the page was on other cpu pagevec ? > + put_page(page); /* Drop the gup reference */ > + Where is get user page (gup) here ? . I guess you mean drop the reference taken above ? > + ret = migrate_pages(&cma_migrate_pages, new_iommu_non_cma_page, > + NULL, 0, MIGRATE_SYNC, MR_CMA); > + if (ret) { > + if (!list_empty(&cma_migrate_pages)) > + putback_movable_pages(&cma_migrate_pages); > + } > + return 0; > +} > + I guess the plan was to not do it one page at a time and switch this to list of pages which we need to migrate. Any reason why that is not tried ? > long mm_iommu_get(unsigned long ua, unsigned long entries, > struct mm_iommu_table_group_mem_t **pmem) > { > @@ -124,15 +175,36 @@ long mm_iommu_get(unsigned long ua, unsigned long entries, > for (i = 0; i < entries; ++i) { > if (1 != get_user_pages_fast(ua + (i << PAGE_SHIFT), > 1/* pages */, 1/* iswrite */, &page)) { > + ret = -EFAULT; > for (j = 0; j < i; ++j) > - put_page(pfn_to_page( > - mem->hpas[j] >> PAGE_SHIFT)); > + put_page(pfn_to_page(mem->hpas[j] >> > + PAGE_SHIFT)); > vfree(mem->hpas); > kfree(mem); > - ret = -EFAULT; > goto unlock_exit; > } > - > + /* > + * If we get a page from the CMA zone, since we are going to > + * be pinning these entries, we might as well move them out > + * of the CMA zone if possible. NOTE: faulting in + migration > + * can be expensive. Batching can be considered later > + */ > + if (get_pageblock_migratetype(page) == MIGRATE_CMA) { > + if (mm_iommu_move_page_from_cma(page)) > + goto populate; > + if (1 != get_user_pages_fast(ua + (i << PAGE_SHIFT), > + 1/* pages */, 1/* iswrite */, > + &page)) { > + ret = -EFAULT; > + for (j = 0; j < i; ++j) > + put_page(pfn_to_page(mem->hpas[j] >> > + PAGE_SHIFT)); > + vfree(mem->hpas); > + kfree(mem); > + goto unlock_exit; > + } > + } > +populate: > mem->hpas[i] = page_to_pfn(page) << PAGE_SHIFT; > } > > -- > 2.5.5 > > -- > To unsubscribe, send a message with 'unsubscribe linux-mm' in > the body to majordomo@xxxxxxxxx. For more info on Linux MM, > see: http://www.linux-mm.org/ . > Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a> -aneesh -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>