On 2/11/19 12:41 PM, Michael S. Tsirkin wrote: > On Mon, Feb 11, 2019 at 11:24:02AM -0500, Nitesh Narayan Lal wrote: >> On 2/11/19 9:17 AM, Michael S. Tsirkin wrote: >>> On Mon, Feb 11, 2019 at 08:30:03AM -0500, Nitesh Narayan Lal wrote: >>>> On 2/9/19 7:57 PM, Michael S. Tsirkin wrote: >>>>> On Mon, Feb 04, 2019 at 10:15:58AM -0800, Alexander Duyck wrote: >>>>>> From: Alexander Duyck >>>>>> >>>>>> Because the implementation was limiting itself to only providing hints on >>>>>> pages huge TLB order sized or larger we introduced the possibility for free >>>>>> pages to slip past us because they are freed as something less then >>>>>> huge TLB in size and aggregated with buddies later. >>>>>> >>>>>> To address that I am adding a new call arch_merge_page which is called >>>>>> after __free_one_page has merged a pair of pages to create a higher order >>>>>> page. By doing this I am able to fill the gap and provide full coverage for >>>>>> all of the pages huge TLB order or larger. >>>>>> >>>>>> Signed-off-by: Alexander Duyck >>>>> Looks like this will be helpful whenever active free page >>>>> hints are added. So I think it's a good idea to >>>>> add a hook. >>>>> >>>>> However, could you split adding the hook to a separate >>>>> patch from the KVM hypercall based implementation? >>>>> >>>>> Then e.g. Nilal's patches could reuse it too. >>>> With the current design of my patch-set, if I use this hook to report >>>> free pages. I will end up making redundant hints for the same pfns. >>>> >>>> This is because the pages once freed by the host, are returned back to >>>> the buddy. >>> Suggestions on how you'd like to fix this? You do need this if >>> you introduce a size cut-off right? >> I do, there are two ways to go about it. >> >> One is to  use this and have a flag in the page structure indicating >> whether that page has been freed/used or not. > Not sure what do you mean. The refcount does this right? I meant a flag using which I could determine whether a PFN has been already freed by the host or not. This is to avoid repetitive free. > >> Though I am not sure if >> this will be acceptable upstream. >> Second is to find another place to invoke guest_free_page() post buddy >> merging. > Might be easier. > >>>>>> --- >>>>>> arch/x86/include/asm/page.h | 12 ++++++++++++ >>>>>> arch/x86/kernel/kvm.c | 28 ++++++++++++++++++++++++++++ >>>>>> include/linux/gfp.h | 4 ++++ >>>>>> mm/page_alloc.c | 2 ++ >>>>>> 4 files changed, 46 insertions(+) >>>>>> >>>>>> diff --git a/arch/x86/include/asm/page.h b/arch/x86/include/asm/page.h >>>>>> index 4487ad7a3385..9540a97c9997 100644 >>>>>> --- a/arch/x86/include/asm/page.h >>>>>> +++ b/arch/x86/include/asm/page.h >>>>>> @@ -29,6 +29,18 @@ static inline void arch_free_page(struct page *page, unsigned int order) >>>>>> if (static_branch_unlikely(&pv_free_page_hint_enabled)) >>>>>> __arch_free_page(page, order); >>>>>> } >>>>>> + >>>>>> +struct zone; >>>>>> + >>>>>> +#define HAVE_ARCH_MERGE_PAGE >>>>>> +void __arch_merge_page(struct zone *zone, struct page *page, >>>>>> + unsigned int order); >>>>>> +static inline void arch_merge_page(struct zone *zone, struct page *page, >>>>>> + unsigned int order) >>>>>> +{ >>>>>> + if (static_branch_unlikely(&pv_free_page_hint_enabled)) >>>>>> + __arch_merge_page(zone, page, order); >>>>>> +} >>>>>> #endif >>>>>> >>>>>> #include >>>>>> diff --git a/arch/x86/kernel/kvm.c b/arch/x86/kernel/kvm.c >>>>>> index 09c91641c36c..957bb4f427bb 100644 >>>>>> --- a/arch/x86/kernel/kvm.c >>>>>> +++ b/arch/x86/kernel/kvm.c >>>>>> @@ -785,6 +785,34 @@ void __arch_free_page(struct page *page, unsigned int order) >>>>>> PAGE_SIZE << order); >>>>>> } >>>>>> >>>>>> +void __arch_merge_page(struct zone *zone, struct page *page, >>>>>> + unsigned int order) >>>>>> +{ >>>>>> + /* >>>>>> + * The merging logic has merged a set of buddies up to the >>>>>> + * KVM_PV_UNUSED_PAGE_HINT_MIN_ORDER. Since that is the case, take >>>>>> + * advantage of this moment to notify the hypervisor of the free >>>>>> + * memory. >>>>>> + */ >>>>>> + if (order != KVM_PV_UNUSED_PAGE_HINT_MIN_ORDER) >>>>>> + return; >>>>>> + >>>>>> + /* >>>>>> + * Drop zone lock while processing the hypercall. This >>>>>> + * should be safe as the page has not yet been added >>>>>> + * to the buddy list as of yet and all the pages that >>>>>> + * were merged have had their buddy/guard flags cleared >>>>>> + * and their order reset to 0. >>>>>> + */ >>>>>> + spin_unlock(&zone->lock); >>>>>> + >>>>>> + kvm_hypercall2(KVM_HC_UNUSED_PAGE_HINT, page_to_phys(page), >>>>>> + PAGE_SIZE << order); >>>>>> + >>>>>> + /* reacquire lock and resume freeing memory */ >>>>>> + spin_lock(&zone->lock); >>>>>> +} >>>>>> + >>>>>> #ifdef CONFIG_PARAVIRT_SPINLOCKS >>>>>> >>>>>> /* Kick a cpu by its apicid. Used to wake up a halted vcpu */ >>>>>> diff --git a/include/linux/gfp.h b/include/linux/gfp.h >>>>>> index fdab7de7490d..4746d5560193 100644 >>>>>> --- a/include/linux/gfp.h >>>>>> +++ b/include/linux/gfp.h >>>>>> @@ -459,6 +459,10 @@ static inline struct zonelist *node_zonelist(int nid, gfp_t flags) >>>>>> #ifndef HAVE_ARCH_FREE_PAGE >>>>>> static inline void arch_free_page(struct page *page, int order) { } >>>>>> #endif >>>>>> +#ifndef HAVE_ARCH_MERGE_PAGE >>>>>> +static inline void >>>>>> +arch_merge_page(struct zone *zone, struct page *page, int order) { } >>>>>> +#endif >>>>>> #ifndef HAVE_ARCH_ALLOC_PAGE >>>>>> static inline void arch_alloc_page(struct page *page, int order) { } >>>>>> #endif >>>>>> diff --git a/mm/page_alloc.c b/mm/page_alloc.c >>>>>> index c954f8c1fbc4..7a1309b0b7c5 100644 >>>>>> --- a/mm/page_alloc.c >>>>>> +++ b/mm/page_alloc.c >>>>>> @@ -913,6 +913,8 @@ static inline void __free_one_page(struct page *page, >>>>>> page = page + (combined_pfn - pfn); >>>>>> pfn = combined_pfn; >>>>>> order++; >>>>>> + >>>>>> + arch_merge_page(zone, page, order); >>>>>> } >>>>>> if (max_order < MAX_ORDER) { >>>>>> /* If we are here, it means order is >= pageblock_order. >>>> -- >>>> Regards >>>> Nitesh >>>> >>> >> -- >> Regards >> Nitesh >> > > -- Regards Nitesh