On 06/09/16 15:49, Aneesh Kumar K.V wrote: > 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 ? Yes, I was being overly conservative with the checks > > >> + >> + 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 ? lru_add_drain_all() is too expensive for a per-page migration. This is best effort. If it is on the pagevec of another CPU, we skip it -- see v3 > > >> + 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 ? > > Fixed in v3 >> + put_page(page); /* Drop the gup reference */ >> + > > Where is get user page (gup) here ? . I guess you mean drop the > reference taken above ? > I say gup, because we'll do gup after this point if migration fails and that we reacquire the reference lost here. > >> + 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 ? > Yes, it is a TODO. Here is my order of preference 1. get this in 2. Get THP migration in -- larger workset 3. Do page aggregation for both 1 and 2 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
