On 2019/2/5 2:15, Alexander Duyck wrote: > From: Alexander Duyck <alexander.h.duyck@xxxxxxxxxxxxxxx> > > 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 <alexander.h.duyck@xxxxxxxxxxxxxxx> > --- > 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 <linux/range.h> > 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); Not a proper place AFAICS. Assume we have an order-8 page being sent here for merge and its order-8 buddy is also free, then order++ became 9 and arch_merge_page() will do the hint to host on this page as an order-9 page, no problem so far. Then the next round, assume the now order-9 page's buddy is also free, order++ will become 10 and arch_merge_page() will again hint to host on this page as an order-10 page. The first hint to host became redundant. I think the proper place is after the done_merging tag. BTW, with arch_merge_page() at the proper place, I don't think patch3/4 is necessary - any freed page will go through merge anyway, we won't lose any hint opportunity. Or do I miss anything? > } > if (max_order < MAX_ORDER) { > /* If we are here, it means order is >= pageblock_order. >